Analyzing LS2 along with comparisons to LS6 & LS3
01-13-2014, 06:38 AM
#1
Burning Brakes
Thread Starter
Analyzing LS2 along with comparisons to LS6 & LS3
The following is a compilation of information from various sources, as noted, with analysis.
Why LS2 Is Not Perceived To Be The Rocket Ship It Really Is
Most performance cars exhibit the feeling of “coming-on-the-cam,” or that someone just turned on the afterburners. A Corvette LS2 does not feel that way because its power curve is smooth and linear. LS2 has great torque and power at low as well as high rpm.
Hib Halverson, writing for Corvette Action Center's website, did a number of in-depth articles about the C6 Corvette when it was a new model. In an interview with Jordan Lee, GMPT Small-Block Chief Engineer, who worked on the LS2 program, Lee said, “At the bottom end, the LS2 is so much fatter than the LS6. There is one thing you gotta be cognizant of: a lot of people think, when they drive very high-performance sport cars, they’re tuned only for high rpm. People perceive that because the bottom end is so weak. You step in the throttle at low rpm and the engine’s flat, but then, all of a sudden, it feels like it’s coming on the cam.” http://www.corvetteactioncenter.com/...5/sequel5.html
“The LS2 has a fat, broad torque curve so it’s very satisfying down low, but you never have that rapid, flip-the-switch type of feel at higher engine speed. For my taste, and I think the majority of sports car drivers agree, it’s more satisfying to have all that responsiveness and still have all the top end.”
Halverson’s response, “I’m with Jordan Lee on the “satisfying” thing (and the C6’s acceleration numbers are with him, too), but I’m not so sure all Corvetters will agree with us because the erroneous belief that “comin’ on the cam” is demonstrative of a powerful engine is so pervasive amongst urban legends in the car hobby. Reality is: if a normally-aspirated engine really has that on-off or on-the-cam feeling, it’s either a race engine or a production engine with poor air flow management, either of which kind of suck on the street.”
“Conversely, the LS2’s bulked-up, low-end adds to its LS6ish top-end to make a torque curve that’s flatter than freakin’ Kansas. Its lack of peakiness makes the car easier and more fun to drive. It idles nicer than an LS6 and has a tiny edge in throttle response. All this comes under the heading of “refinement.”
Jim Schindler mentioned this a number of times when comparing his 2005 LS2 Corvette to a friend’s modified C5 Z06: “When I got my first C6, a friend who has a 2002 Z06 with headers, tune, etc. (382 rwhp) came over and we drove each others cars. His FELT like it would run off and leave my C6 for dead. But a funny thing happened side-by-side. Even with his mods, they were damn near equal—his only advantage was slight at higher speeds.”
http://forums.corvetteforum.com/c6-c...post1561240803
http://forums.corvetteforum.com/c6-c...post1561765623
http://forums.corvetteforum.com/c6-c...post1581962108
TTRotary had a similar experience: “When I bought the C6, I was pretty sure it was noticeably slower than my Z. Since I still had it, I got a friend to drive and we did some highway pulls from 45 or so. To my surprise, the C6 was right there with the Z through 120. It was interesting, the C6 would pull on the Z at the low end of each gear and the Z06 would catch it back on the top end of the gear. The C6 was Z51 so same gearset. As an experiment, we swapped rear wheels. The Z could no longer pull. So I'd conclude that the 6.0L is a pretty stout motor if it can move a heavier car that well despite have same HP. Also, the C6 tune, as you know, is a dog. After Shawn's tune, my LS2 has that same razor-sharp response the LS6 had.” http://forums.corvetteforum.com/c6-c...post1558790425
Shortly after LS2’s introduction in the C6 Corvette, a major auto publication, in news-clip format,—I believe it was Motor Trend—made a direct comparison between LS2 and LS6 engines. Identical Cadillac CTS-v cars, with different engines, were used in testing. The LS2 car out-accelerated the LS6 Cadillac, leading the magazine to conclude that LS2 was the stronger engine.
LS2 Corvettes do not feel as fast as they really are.
Another problem the LS2 has is spending too much time in low, “knock retard,” timing tables. Corvette LS2 engines have a 10.9:1 compression ratio and are designed to run on 93 octane gas in optimal conditions.
Hib Halverson wrote the following: http://www.corvetteactioncenter.com/...5/sequel7.html “General Motors’ 2004 media Product Information Guide, or PIG (“media pig”-hidden meaning, perhaps?) says 93-octane gasoline is “recommended” for use in Corvettes. Owner’s Manuals for ’04 say to use ”…91-octane or higher for best performance.” While there seems to be a difference between what GM tells media and what it tells owners (certainly not the first time that’s happened), most people will run LS2s on whatever premium unleaded they find. Generally, this means 93-octane along the East Coast and parts of the Midwest and 91-octane in most of the rest of the country.”
“LS2, like all Corvette engines since 1982, has computer-controlled spark timing and part of that is a feedback loop which eliminates detonation which can damage the engine. When the knock sensors signal the engine controller that detonation is occurring, in milliseconds, the controller retards timing—we call this “knock retard”—until detonation stops and, once it stops; timing is restored. This feedback process goes on constantly such that spark timing is always at the optimum level for best performance, highest fuel economy, lowest emissions and the octane of the gasoline being used.”
“In nominal atmospheric conditions, 93-octane is adequate for the LS2 to perform optimally with minimal knock retard to control detonation, however, some of my chassis dyno testing of pump gasolines leads me to speculate that, to run detonation-free under the worst conditions, i.e.: wide-open-throttle, heavy load, low humidity, sea level (or near so) pressure, high intake air temperature and high coolant temperature—the LS2 probably needs about 95-octane.”
“With the engine calibrated for 93-octane, that extra last bit of performance during severe duty requiring perhaps as much as 95-octane, Corvetters in a fair amount of the country stuck with 91 and a few errant owners trying to use regular; feedback spark control and knock retard are what allows the engine to produce highest-performance on good gas but not be damaged by detonation when running on gasoline of less than 93-octane.”
Corvette forum member, TTRotary, commented on the effect knock retard engine management has on his LS2 Corvette in hot weather—“Now for the caveat: for some reason (perhaps aggressive engine management due to high compression ratio), the LS2 in the C6 just falls apart on a hot day. 68-75F, the thing is a monster—I like it better than the LS6. But give it 95F and turn on the AC, and it becomes a DOG.” He also commented on knock retard being mistaken as torque management (TM)—“The good news is I have never encountered TM on my car, even when temps are cool and I rip the 1-2 shift hard. Maybe engine management is what people have confused with TM. If ever a car needed cold air intake and a tune, it’s this one.” http://forums.corvetteforum.com/c6-t...post1552336590
Corvette forum member, Yawlak80-86, made excellent posts on octane requirements for LS2: http://forums.corvetteforum.com/c6-t...post1579509447 and http://forums.corvetteforum.com/c6-t...post1579518315. He said, “The problem is especially bad with LS2s as they have too much timing combined with too high a compression ratio from the factory. They spend most of their time on the low tables when using 91 and still ping. . .When I go to the track, I run a blend of 100 octane race fuel w/ 91 octane pump gas making at least 95 octane so I can run adequate timing." He also mentioned the LS3—“The owners manuals are not gospel. LS3s have a slightly lower compression ratio than the LS2 and LS7. They also have much better heads than the LS2 (perhaps the quench zone is relocated in the cylinders as a result—I’m not positive). Perhaps these are some of the reasons they say the LS3s are good with 91-octane but I can tell you with certainty, they are not, at least not in my neck of the woods. I can also tell you that I had no pinging issues on the East Coast with premium top tier fuels, (except for Shell).”
Corvette forum member, Tommy D, made a post which supports the contention that knock retard engine management is not as intrusive on the LS3—“Remember that torque management cannot be tuned out on launch and is not as intrusive on the later C6s.” http://forums.corvetteforum.com/c6-t...post1577287695
On page 6 of “C6 Naked and Exposed – The Sequal; Finally . . . We Drive It!!!," GMPT engineer Jordan Lee states, “When you bump the compression, you need better combustion efficiency, so you're less prone to knock (underline my emphasis); but if you do get knock; you need a control system which can react very quickly so that it’s unobtrusive to the driver.” http://www.corvetteactioncenter.com/...5/sequel6.html
On page 5 of “Ruthless Pursuit of Power: 2008 Edition,” Hib Halverson had this to say about LS3 combustion quality: http://www.corvetteactioncenter.com/...ls3_page5.html “The best combustion quality occurs when the air fuel mixture in the chamber is distributed uniformly, or is “homogenous”, throughout the chamber. The process of becoming homogenous, or as close to it as possible, occurs in the latter stage of the intake valve event and continues once the valve is closed and the piston starts upward. Not only does the upward piston movement compress the air-fuel mix but it also causes it to swirl and tumble and that further mixes it up making it more homogenous. The LS2/LS6 chamber had great swirl but not very good tumble. The air fuel mix needs to be doing both if the goal is homogeneity right when the spark comes.” A bulge added to LS3’s combustion chamber caused the mixture to tumble as well as lowering the compression ratio.
Combustion quality along with a lower compression ratio allows LS3 engines to spend less time in “knock retard” than LS2. This is why LS3, in combination with a somewhat more efficient drivetrain, shows better numbers on many chassis dynos than an LS2 engine with only 20 less horsepower.
Anthony @ LGMotorsports did a back-to-back comparison of a LS2 Corvette, LS3 Camaro and a 5.0 Mustang. Here it is: http://forums.corvetteforum.com/c6-t...post1576411472
LS3 Camaro Max power was 374.35 RWHP; LS2 Corvette was 358.99 RWHP. Difference is 15.36 HP. Camaro LS3 Certified HP is 426; LS2 Certified HP should have been 411. That is a 15 HP difference. I believe a back-to-back comparison means all dyno runs were done at the same time. It looks like LS2 was on the right timing table.
LG Motorsports’ back-to-back comparison shows that the power differential between LS2 and LS3 is greater in midrange rather than at peak power rpm levels. LS3 surpasses the 15 horsepower difference at about 3500 rpm . This continues until peak power is reached at 5900 and 6000 rpm where there is a 15 horsepower difference. The chart also seems to show LS3 losing power more rapidly than LS2 after peak power levels are reached. Projecting LS3’s power curve to 6600 rpm, it looks like LS2 and LS3 power levels will be practically the same. But don’t forget, this is for the 426 HP LS3, not the 430 HP Corvette LS3.
GM’s Corvette power and torque chart shows that, unlike LG Motorsports, the greatest power differential between LS2 and LS3 is reached at peak levels. Scroll down the following link to see the GM chart (http://www.corvetteactioncenter.com/...ls3_page6.html). This chart shows that LS2/LS3 power and torque are nearly the same until about 3500 rpm, where LS3 starts climbing at a faster rate. LS3 power and torque change their angle of ascent, whereas, LS2 continues rising at a steady rate. LS3 acts more like an LS6, so “coming-on-the-cam” is a noticeable sensation.
How LS2 made 20+ HP over ’01 LS6 and LS3 made 20 HP more than LS2
Dividing ’01 LS6’s 385 horsepower by its 346 cubic-inches results in 1.1127 HP per cubic-inch. Multiplying that figure by LS2’s 364 cubic-inches results in 405 HP. Both engines use the same cylinder heads and camshaft, but LS2 has a power-increasing higher compression ratio (10.9:1 advertised – 10.87:1 actual) than LS6 (10.5:1).
LS2 has a single catalytic converter mounted right after each exhaust manifold rather than the close-coupled converters—known as pups—that were combined with the under-car converters on the ’01 LS6. Having one converter on each side reduced back pressure by 2-inches of mercury (16%), which on its own is worth about five horsepower. Along with exhaust manifolds that flow 4% better and exhaust pipes with smoother bends, LS2 benefits by having longitudinally-mounted mufflers with larger internal volume resulting in 10% less restriction than the transverse mufflers with four, 90-degree tube bends that were mounted on all C5 Corvettes. These improvements resulted in a total of 20% less back pressure in the exhaust system.
A redesigned induction system (air box and duct) resulted in 31% better airflow. Most of this increase was the result of C6 Corvettes becoming both front-breathers, air entering through the grill, and bottom-breathers, air entering from the bottom of the car—split 60% front; 40% bottom. Base C5 Corvettes were bottom-breathers only, but the Z06 LS6 had additional air ducted directly to the air-filter box from openings in the front fascia—C6 air flow was an improvement over the Z06. LS2 uses the same mass-air-flow sensor (MAF) as the '02 to '04 LS6, but with the honey-cell flow straightener found in the '01 LS6. Throttle body size went from 76-mm on the LS6 to 90-mm on LS2. Fuel injector capacity increased to 32.5 lb/hr. (4.1 g/sec.) from LS6's 28.5 lb/hr. (3.6 g/sec.).
LS2’s intake manifold was produced using the vibration welded process. It is glass-filled and made out of Nylon 6 rather than Nylon 66, which was used in LS6’s lost-core-process manifolds. The bell-mouth is larger and runner geometry has been optimized for a six-liter engine. The combined result of all intake/induction system improvements is an air flow increase of 15%.
Vibration welding has resulted in seams that allow crosstalk—air passing between runners—which is detrimental to smooth air flow and results in some lost power. GM went back to the lost-core process for the LS3 engine but used Nylon 6. John Rydzewski, Assistant Chief Engineer for Small Block Passenger Engines: “A vibration-welded intake has different shells. One port can be a combination of an upper portion and a bottom portion with the runners welded together on the side. It’s a pretty good seam, but there might be a little crosstalk (port-to-port leakage) which can rob you of some power. We had seen that in some applications, so we went to a lost-core intake (on LS3).” http://www.corvetteactioncenter.com/...ls3_page6.html Vibration welding was also used in the production of LS7 intake manifolds; however, at some point the seams were sealed to prevent crosstalk. I doubt that sealing was ever used on LS2 intakes.
LS2’s pistons have a true flat-top design with all three rings having lower tension than LS1 and LS6 rings. Lower tension reduces friction to free up horsepower. The pistons also have full floating wrist pins that help reduce the piston slap noise that’s common on Generation III engines (LS1, LS6). Gen IV engine blocks (LS2, LS3) have siamesed cylinder bores, meaning that a water slot between bores is unnecessary for adequate cooling and that all bores have a solid, uninterrupted connection. This resulted in a stronger block that is less prone to heat distortion in the cylinders. Less bore distortion means less friction and pumping losses.
Both intake and exhaust airflow are better on LS2 Corvettes than the 2001 LS6. LS2 uses the same cam and heads as the ’01 Z06. With a higher compression ratio, 18 more cubic-inches, induction/intake and exhaust flow better than 2002 to 2004 LS6 engines and various internal modifications that decreased friction and pumping losses, LS2 should have been rated at the 406 or 407 SAE net horsepower that Tony Holloway told me LS2 engines produce. In applications using the LS6 385-horse cam, torque equals horsepower, so LS2 torque should match its horsepower rating.
LS2 never received an official certified rating under the new, for model year 2006, SAE J1349 procedures. But GM, knowing that the new protocol was coming, rated LS2 using the new methods long before the engine received its official 400 horsepower rating. Under SAE certified protocol, LS2 rated between 410 and 415 horsepower. If the new rating system had been ready for the 2005 model year, LS2 would NOT have been rated at 400 horsepower.
The 2002 version of LS6 and 2008 LS3 made 20 horsepower more than their predecessors. Both engines used the same cam intake profiles, but LS3’s exhaust profile is the same that was used in the ’01 LS6 and LS2 cams. Along with more aggressive cams, power gains were derived from exhaust back pressure reductions on the '02 LS6 and better flowing heads on LS3.
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The following six paragraphs were taken from an article titled 2002 LS6 Engine – The Ruthless Pursuit of Power: The Sequel by Hib Halverson, from the January, 2002 issue of GM High-Tech Performance magazine: http://www.gmhightechperformance.com...e/viewall.html
According to LS6 camshaft engineer, Jim Hicks, in comparing the ’01 LS6 cam to the ’02 cam: “You can do a direct A/B comparison and there’s an easy 8-10 HP there, whether you change the back pressure or not. There are other changes in the ’02 package—exhaust system and induction system—which increase the power more. The overall power increased about 20 HP and the cam was half of it. Again, that’s because it’s a short-duration design with low overlap so it’s not really affected that much by back pressure.”
Corvette Chief Engineer, Dave Hill said, “We never set out to obsolete the 2001 LS6. The horsepower increase was possible only after we completed a lengthy development of a new catalyst. I want to set the record straight: the 2001 was the best Z06 we could possibly make and 2002 is better because new catalyst technology let us get the back pressure down, increase the breathing and make that power increase.”
Assistant Chief Engineer for Gen III Passenger Car Engines, John Juriga, added, “In 2000 we had to meet the LEV standard here in California, so we added close-coupled converters up front on the California package, our ‘pups’ as we call ‘em. In 2001 we carried those pups across the board, including on the LS6. Even while we were implementing that, we were working on a design that would eliminate those pups. This reduced back pressure by two inches of mercury. On its own, that was worth about 5 HP. That seems not much, but if you reduce back pressure by even small amounts, you can make a bigger gain with improvements on the induction side, especially with the cam.”
More airflow from the new cam and less back-pressure from the new cats drove some other improvements on the induction side. For MY02, LS6 gets a new air filter assembly. It’s similar to the ’01 unit in that it has an additional air intake opening on its cover, but the extra opening is larger. GM also did what GMHTP readers have been doing for years with MAFs--remove the air flow straightener screen. This allowed for a less restrictive path through the sensor.
There were no changes to either the LS6’s intake manifold or its cylinder heads. John Juriga: “The intake manifold was already pretty darn good. We designed it to handle additional flow rates and not require retool the very next year because composite intakes are very expensive to retool and develop. We made sure it would flow more air than we needed in the first year. The same was true with the heads.”
A change in engine air flow significant enough to provide 20 more horsepower also demanded a small change in the engine’s fuel and spark curves. This was done with slight changes in the PCM calibration. There was no change in injectors or fuel pressure.
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Low hanging fruit had already been picked for the LS2 engine to come up with 20+ more horsepower than the 385-HP LS6, so LS3 needed a significant upgrade for an equal increase in power. LS3 had no changes in the exhaust system after the cylinder head exhaust ports and there wasn't as great a difference on the induction side before air entered the intake manifold. LS3’s intake manifold was again made using the lost-core process and flowed 2-3% better than the LS2 intake. To add 20 more horses, there had to be a major upgrade in the cylinder heads along with the new cam. LS3 did not have the advantage of eighteen more cubic-inches (5.2% more than LS6) and the higher compression ratio that LS2 had over the LS6. LS3 was only twelve cubic-inches or 3.3% larger than LS2 and its compression dropped from LS2’s 10.87:1 to 10.7:1.
A Corvette Action Center article titled Ruthless Pursuit of Power: 2008 Edition by Hib Halverson http://www.corvetteactioncenter.com/...ls3_page1.html describes the improvements that increased LS3 power:
Assistant Chief Engineer for Small Block Passenger Engines, John Rydzewski, talks about improvements in the intake manifold: “We also reshaped it for better flow. Yoon Lee, who’s been on the program for a few years, did the development. Compared to LS2, he reduced restriction by 2-3% at 13.5mm lift. It’s just a smoother path, right down to the head.”
Compared to LS2/LS6 cylinder heads, LS3 heads flow much better. According to Lou Oniga, Design Responsibility Engineer (DRE) for Small-Block Cylinder Heads, “The flow numbers are (average) 17% improvement on the intake and 6.2% on the exhaust.”
LS3's camshaft was improved with a 405-HP, LS6 intake lobe profile--exhaust lobe profile from the 385-HP LS6/LS2 cam was retained.
LS3 fuel injectors come from LS7 and flow 5-gram/sec.--LS2 injectors flow 4.1-gram/sec. The throttle body carries over from the LS2. There are no functional changes to the positive crankcase ventilation (PCV) system. The induction system ahead of the throttle body is from the Z06, but with some quarter-wave tuners added to attenuate certain frequencies of intake noise. Overall, induction/intake restriction has been reduced by 10% (Corvette Quarterly, Fall 2007, page 50). The exhaust manifolds are similar to the units introduced in 2005 on LS2, but have a slight change in each exhaust runner where it bolts to the head to match the revised exhaust port exits. Exhaust pipes after the manifold are the same as the LS2, but when the NPP option is included, a flap in each muffler opens allowing exhaust gases to flow more freely...adding 6-horsepower.
There are improvements in the LS3 block: Main bearing webs are about 20% stronger and windows, which enhance “bay-to-bay breathing” in the interest of oil control and reduced parasitic loss, have been somewhat enlarged. LS3's ring package has once again been changed: The top two compression rings have the same tension as LS2 rings; the bottom, oil ring tension was increased. All rings have a .25-degree increase in grove tilt. Increased grove tilt and oil ring tension improved oil control, but more tension adds friction, which is a drag on power.
Summary
LS2 vs ’01 LS6 (http://www.corvetteactioncenter.com/...5/sequel5.html) (http://www.gmhightechperformance.com..._look_feature/) (Corvette: Sports Car Super Star by the Auto Editors of Consumer Guide, 2005, Publications International, Ltd., page 391) (The Complete Book of Corvette: Every Model Since 1953 by Mike Mueller, 2006, Motorbooks – MBI Publishing Company, pages 315 & 328)
LS2 Exhaust System – New exhaust manifold is capable of 4% better flow; back pressure reduced by 2-inches of mercury (16%) with a single catalytic converter attached to exhaust manifolds rather than close-coupled pup-cats and under-car converters; smoother exhaust-pipe bends; 10% less back pressure with the elimination of four, 90-degree tube bends at mufflers and less restrictive larger internal volume mufflers. In total, the reduction in exhaust back pressure is 20% over the 2001 base system.*
LS2 Intake System – Significant improvement was made because C6 Corvettes became both front- and bottom-breathers. Intake manifold: runner geometry optimized for six-liter displacement; larger bell-mouth; crosstalk causes slight power loss. Throttle-body size increased from 76-mm to 90-mm; induction system (air box and duct) redesigned for lower restriction—31% lower restriction than LS1 induction system.* Overall, intake/induction system airflow has been improved by 15%.
*Note: Beginning with the 2001 production year, LS1 and LS6 engines used the same intake and exhaust manifolds, MAF sensor, and throttle body. These improvements were worth an added ten horsepower to the LS1. For model-year 2000, the addition of pup-cats to California Corvettes resulted in a loss of five horsepower, which means these cars actually made an unadvertised 340 horsepower. The same power reduction would have happened to all 2001, LS1 Corvettes if it hadn’t been for the intake and exhaust upgrades. Chevy never publicized the California power loss and didn't rerate the engine until 2001 (350 HP).
Cylinder heads and cam – Heads are same as 2001 to 2004 LS6; cam is same as 2001 LS6
Engine – Compression ratio increased from 10.5:1 to 10.87:1; displacement increased by eighteen cubic-inches or 5.2%; lower tension piston rings free up horsepower; siamesed bores result in a stronger block and cylinders with less bore distortion, friction and pumping losses.
LS3 vs LS2
LS3 Exhaust System – no change from LS2
LS3 Intake System – Intake manifold restriction reduced by 2-3% and made with lost-core method—no lost power; throttle-body same as LS2; induction system same as Z06, but with quarter-wave tuners; overall induction/intake restriction reduced by 10%.
Cylinder heads and cam – Significant cylinder head upgrade with average intake flow increased by 17% and exhaust increased by 6.2%; cam intake profile same as ’02 LS6, exhaust profile same as LS2.
Engine – Compression ratio dropped from 10.87:1 to 10.7:1; displacement increased by twelve cubic-inches or 3.3%; reduced parasitic loss from increased bay-to-bay breathing; a .25-degree increase in piston-ring grove tilt and higher-tension oil rings resulted better bore sealing and oil control, but increased power-robbing friction.
LS2 improvements resulted in a 21 or 22 horsepower increase over the 385-HP LS6 and LS3 improvements resulted in a 20 horsepower increase over LS2. Compared to LS2, LS3 had no increase in exhaust flow after exhaust gases left the heads and induction/intake flow restriction was reduced by 10%. LS3’s cam was not as significant an improvement as the 405-HP LS6 cam was over the 385-HP version. The 405-HP LS6 cam gained from 8 to 10 HP, so in my opinion, LS3’s cam gained somewhat less. To get another 11-14 horses, LS3 needed a major flow increase from its heads (17% intake - 6.2% exhaust), especially considering that LS3's compression dropped compared to LS2 and it had 36.5% less increase in cylinder volume in comparison to LS2’s increase over LS6. LS2's largest power gains came from increases in compression and cubic-inches, but significant air-flow upgrades--15% on the intake side and 20% on exhaust--were the drivers of more power and torque at both low and high rpm levels without using a bigger cam.
During engine development, Corvette's Chief Engineer and Vehicle Line Executive, Dave Hill, wanted LS2 power to be where the Z06 LS6 was (405 HP) without the premium hardware (longer, hollow-stem valves with potassium-sodium filled exhaust stems), although LS2 did get the stiffer '02 - '04 LS6 valve springs for high rpm stability. I bet he was satisfied with the outcome. GMPT’s Executive Director of Engine Engineering, Sam Winegarden: “Chief engineer Dave Hill said he would really like to take all standard Corvettes to where the Z06 was, and we said that jived with where we saw our competitors, from an engine perspective, going in terms of horsepower. We continually benchmark our engines against our competitors and look at the trends.” (Corvette C6 by Phil Berg, 2004, Motorbooks International, page 63)
Jim Hall, owner of Corvette Forum vendor, Halltech Systems, LLC (Halltech), started a thread with an interesting post on 4/29/2004 that was ahead-of-the-curve. I was not able to find his original post, but it was quoted in another post: https://www.corvetteforum.com/forums...post1550170810 (The beginning of Jim's thread was deleted. If you look at post 1 and 2, it becomes clear these were not the first two posts of the thread. They were made on 3/19/05, almost a year after the thread was started on 4/29/04, and then renumbered. Sometime after the original thread began, GM expressed great displeasure with a vendor's post on this forum. It could have been this one--my memory of the details has faded with time. Obviously much of the original thread was eliminated, so we only have the following quote from post #9 as evidence of Jim Hall's original post.)
Originally Posted by Jim Hall
The C6 is actually 420+ HP.
Why do I suggest that? Three years ago, I posted a thread on the corvetteforum, with a poll asking how many folks would purchase a C5 Coupe with a LS6 option. There were many interested members.
Some quoted Dave Hill as stating that he would never put the Z06 motor in the Coupe or Convertible.
The C6 is just that and more.
400 HP is ridiculous for the amount of internal changes found in the LS2. It is actually a hot rod Z06 motor in sheeps clothing.
A quick comparison: 2004 Z06 has a smaller throttle body-76mm vs. 90 mm for the 2005 C6. The Z06 has a 5.7 liter motor vs. the 6.0 liter LS2. The intake manifold has been redesigned to accommodate the better flow characteristics of the throttle body, and the heads are also improved from a port configuration standpoint. i.e. a ported LS6 head. The compression ratio was automatically increased with the new swept volume from the additional displacement and Z06 combusion chambers to 10.9:1 vs. 10.5:1. Iridium plugs, and hotter coils mean better combustion.
Bigger fuel injectors than the 2004 Z06 with four hole injectors are rated at 4.1 g/s vs the older 3.67 g/s (both at 400 kilopascal or 58 psi rail pressure)
The Z06 heads being utilized flow 15% more air on the intake side, and 21% more on the exhaust port side. 2.00"/1.55" valves are the same steel valves as the LS1. but the springs are Z06.
The exhaust manifolds flow 4% better than the Z06 exhaust manifold (our dyno testing in 2001 suggested that shorty headers vs. the LS6 headers, showed zero improvement in horsepower or torque, so GM has done some homework here) with the straight through mufflers reducing backpressure 10%, and now no pup cats! Finally. No A.I.R. pump! Bay to bay breathing as in the Gen III Z06, has been a part of the LS1 and LS6 for a few years now.
The cam used is the 2001 Z06 cam, with a .525"/.525" lift (2004 Z06 cam is .555"/.551" and similar duration, so here you can subtract 10 RWHP, for the C6 with the same head port design, but with the increase port flow, the actual loss from a lower lift may be insignificant. We have the present Z06 cams, ready to install as soon as our C6 comes in.
They have also gone back to the lower tension rings found in the 2001 Z06, but without the oil consumption problems, which means less frictional losses. Anodized ring lands, may help strengthen the lands, but not from forced induction senarios. I am very disappointed that forged pistons were not used.
GM would have you compare the LS2 to the LS1 to keep the Z06 hot rodders happy, but the truth is out there. The real comparison should be the LS2 vs. the LS6. The LS2 is the new KING of horsepower, no matter how GM spins it.
With all of the above changes to the basic Z06 platform, do they expect anyone to believe that there is only 5 HP LESS than the Z06...???
From a marketing standpoint, it would kill the remaining 2004 Z06 sales, if the new C6 became available with 420 advertised HP.
One more thing. When the Z06 (LS7) motor hits the scene, the 3 valve head design, dry sump, and 427 cid will bump the horsepower to 535. GM will claim much less on paper.
Jim Hall
[Modified by Jim Hall, 7:53 PM 4/29/2004]
At the upscale Detroit Opera House, on January 4, 2004, GM held a snazzy, invitation only event for the unveiling of the brand new C6 Corvette with Rick Wagoner, GM Chairman and CEO, as the main speaker. Perhaps Jim Hall was at this event, or some other information session, learning about what makes Corvette’s new, LS2 engine tick. Jim was obviously well informed, because he was 100% correct with his 420+ horsepower prediction with a caveat. He stated, “…you can subtract 10 RWHP…” for the cam, which results in the same 410+ horsepower that preproduction LS2s rated under the imminent, certified protocol.
Power Progression: LS6 – LS2 – LS3
LS6 heads were originally designed with more than enough air flow to accommodate a 405 horsepower LS6 engine. So, identical LS2 heads (243 castings) already had enough air flow to feed 406 or 407 HP as measured with the original SAE J1349 rating procedures used by all U.S. auto manufacturers from 1972 through 2005. When Chevy rated the preproduction LS2 with what became the new, for model year 2006, SAE certified protocol, it measured between 410 and 415 HP. All GM engines that were rated under both standards had higher horsepower numbers with the new certified protocol.
A redesigned C6 platform allowed for better induction and exhaust air flow than was possible with the C5 platform, including the C5 Z06. LS2’s increased air flow, compression and cubic inches resulted in a stronger engine than the 2002 to 2004, 405-HP LS6.
Two sets of heads were developed for the LS7 engine. The first heads were ultimately rejected because they couldn’t produce the desired power. After some additional work, these heads were used on the LS3. LS3’s fuel injectors and induction system ahead of the throttle body (MAF sensor, air box and duct) also came from the LS7—these parts flowed more fuel and air than necessary, but since they were already inventoried, using them eliminated extra engineering, development, production, and inventory costs. LS3’s throttle body and exhaust system, except for a small change in the manifold to match the head’s reshaped exhaust ports, were from the LS2. Using off-the-shelf parts was a cost effective way to reach 430 SAE certified horsepower in a normally aspirated, overhead valve, 6.2-liter engine.
Horsepower per cubic inch
SAE net (pre-2006)
2001 LS6 – 1.1127 (385/346)
2002 LS6 – 1.1705 (405/346)
2005 LS2 – 1.1154 (406/364)
SAE certified (post-2005)
2005 LS2 – 1.1291 (411/364)
2008 LS3 – 1.1436 (430/376)
Increasing an engine’s cylinder volume will increase torque, however, without corresponding increases in air flow and/or compression, power per cubic-inch will decrease. LS2 and LS3 engines had significant increases in air flow. LS2’s increased compression plus improved intake and exhaust flow were spread over a 5.2% increase in cylinder volume and LS3’s improved heads and cam along with better intake flow were spread over a 3.3% cylinder volume increase. Higher volume increases require correspondingly higher air-flow rates to maintain equal power levels per cubic-inch of total cylinder volume. This explains why LS3’s horsepower per cubic-inch is greater than LS2’s (LS2’s cylinder volume increase was 36.5 % greater than LS3’s) and why the 2002 LS6 had a significant increase in power per cubic-inch over the 2001 LS6 (no change in cylinder volume).
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For more information on LS2 Corvette evaluations, comparisons and history, see the Corvette Forum thread titled LS2 Certified Horsepower?—For LS2 Guys at the following address: http://forums.corvetteforum.com/c6-c...-ls2-guys.html Information that you just read in this post is included in the thread.
Why LS2 Is Not Perceived To Be The Rocket Ship It Really Is
Most performance cars exhibit the feeling of “coming-on-the-cam,” or that someone just turned on the afterburners. A Corvette LS2 does not feel that way because its power curve is smooth and linear. LS2 has great torque and power at low as well as high rpm.
Hib Halverson, writing for Corvette Action Center's website, did a number of in-depth articles about the C6 Corvette when it was a new model. In an interview with Jordan Lee, GMPT Small-Block Chief Engineer, who worked on the LS2 program, Lee said, “At the bottom end, the LS2 is so much fatter than the LS6. There is one thing you gotta be cognizant of: a lot of people think, when they drive very high-performance sport cars, they’re tuned only for high rpm. People perceive that because the bottom end is so weak. You step in the throttle at low rpm and the engine’s flat, but then, all of a sudden, it feels like it’s coming on the cam.” http://www.corvetteactioncenter.com/...5/sequel5.html
“The LS2 has a fat, broad torque curve so it’s very satisfying down low, but you never have that rapid, flip-the-switch type of feel at higher engine speed. For my taste, and I think the majority of sports car drivers agree, it’s more satisfying to have all that responsiveness and still have all the top end.”
Halverson’s response, “I’m with Jordan Lee on the “satisfying” thing (and the C6’s acceleration numbers are with him, too), but I’m not so sure all Corvetters will agree with us because the erroneous belief that “comin’ on the cam” is demonstrative of a powerful engine is so pervasive amongst urban legends in the car hobby. Reality is: if a normally-aspirated engine really has that on-off or on-the-cam feeling, it’s either a race engine or a production engine with poor air flow management, either of which kind of suck on the street.”
“Conversely, the LS2’s bulked-up, low-end adds to its LS6ish top-end to make a torque curve that’s flatter than freakin’ Kansas. Its lack of peakiness makes the car easier and more fun to drive. It idles nicer than an LS6 and has a tiny edge in throttle response. All this comes under the heading of “refinement.”
Jim Schindler mentioned this a number of times when comparing his 2005 LS2 Corvette to a friend’s modified C5 Z06: “When I got my first C6, a friend who has a 2002 Z06 with headers, tune, etc. (382 rwhp) came over and we drove each others cars. His FELT like it would run off and leave my C6 for dead. But a funny thing happened side-by-side. Even with his mods, they were damn near equal—his only advantage was slight at higher speeds.”
http://forums.corvetteforum.com/c6-c...post1561240803
http://forums.corvetteforum.com/c6-c...post1561765623
http://forums.corvetteforum.com/c6-c...post1581962108
TTRotary had a similar experience: “When I bought the C6, I was pretty sure it was noticeably slower than my Z. Since I still had it, I got a friend to drive and we did some highway pulls from 45 or so. To my surprise, the C6 was right there with the Z through 120. It was interesting, the C6 would pull on the Z at the low end of each gear and the Z06 would catch it back on the top end of the gear. The C6 was Z51 so same gearset. As an experiment, we swapped rear wheels. The Z could no longer pull. So I'd conclude that the 6.0L is a pretty stout motor if it can move a heavier car that well despite have same HP. Also, the C6 tune, as you know, is a dog. After Shawn's tune, my LS2 has that same razor-sharp response the LS6 had.” http://forums.corvetteforum.com/c6-c...post1558790425
Shortly after LS2’s introduction in the C6 Corvette, a major auto publication, in news-clip format,—I believe it was Motor Trend—made a direct comparison between LS2 and LS6 engines. Identical Cadillac CTS-v cars, with different engines, were used in testing. The LS2 car out-accelerated the LS6 Cadillac, leading the magazine to conclude that LS2 was the stronger engine.
LS2 Corvettes do not feel as fast as they really are.
Another problem the LS2 has is spending too much time in low, “knock retard,” timing tables. Corvette LS2 engines have a 10.9:1 compression ratio and are designed to run on 93 octane gas in optimal conditions.
Hib Halverson wrote the following: http://www.corvetteactioncenter.com/...5/sequel7.html “General Motors’ 2004 media Product Information Guide, or PIG (“media pig”-hidden meaning, perhaps?) says 93-octane gasoline is “recommended” for use in Corvettes. Owner’s Manuals for ’04 say to use ”…91-octane or higher for best performance.” While there seems to be a difference between what GM tells media and what it tells owners (certainly not the first time that’s happened), most people will run LS2s on whatever premium unleaded they find. Generally, this means 93-octane along the East Coast and parts of the Midwest and 91-octane in most of the rest of the country.”
“LS2, like all Corvette engines since 1982, has computer-controlled spark timing and part of that is a feedback loop which eliminates detonation which can damage the engine. When the knock sensors signal the engine controller that detonation is occurring, in milliseconds, the controller retards timing—we call this “knock retard”—until detonation stops and, once it stops; timing is restored. This feedback process goes on constantly such that spark timing is always at the optimum level for best performance, highest fuel economy, lowest emissions and the octane of the gasoline being used.”
“In nominal atmospheric conditions, 93-octane is adequate for the LS2 to perform optimally with minimal knock retard to control detonation, however, some of my chassis dyno testing of pump gasolines leads me to speculate that, to run detonation-free under the worst conditions, i.e.: wide-open-throttle, heavy load, low humidity, sea level (or near so) pressure, high intake air temperature and high coolant temperature—the LS2 probably needs about 95-octane.”
“With the engine calibrated for 93-octane, that extra last bit of performance during severe duty requiring perhaps as much as 95-octane, Corvetters in a fair amount of the country stuck with 91 and a few errant owners trying to use regular; feedback spark control and knock retard are what allows the engine to produce highest-performance on good gas but not be damaged by detonation when running on gasoline of less than 93-octane.”
Corvette forum member, TTRotary, commented on the effect knock retard engine management has on his LS2 Corvette in hot weather—“Now for the caveat: for some reason (perhaps aggressive engine management due to high compression ratio), the LS2 in the C6 just falls apart on a hot day. 68-75F, the thing is a monster—I like it better than the LS6. But give it 95F and turn on the AC, and it becomes a DOG.” He also commented on knock retard being mistaken as torque management (TM)—“The good news is I have never encountered TM on my car, even when temps are cool and I rip the 1-2 shift hard. Maybe engine management is what people have confused with TM. If ever a car needed cold air intake and a tune, it’s this one.” http://forums.corvetteforum.com/c6-t...post1552336590
Corvette forum member, Yawlak80-86, made excellent posts on octane requirements for LS2: http://forums.corvetteforum.com/c6-t...post1579509447 and http://forums.corvetteforum.com/c6-t...post1579518315. He said, “The problem is especially bad with LS2s as they have too much timing combined with too high a compression ratio from the factory. They spend most of their time on the low tables when using 91 and still ping. . .When I go to the track, I run a blend of 100 octane race fuel w/ 91 octane pump gas making at least 95 octane so I can run adequate timing." He also mentioned the LS3—“The owners manuals are not gospel. LS3s have a slightly lower compression ratio than the LS2 and LS7. They also have much better heads than the LS2 (perhaps the quench zone is relocated in the cylinders as a result—I’m not positive). Perhaps these are some of the reasons they say the LS3s are good with 91-octane but I can tell you with certainty, they are not, at least not in my neck of the woods. I can also tell you that I had no pinging issues on the East Coast with premium top tier fuels, (except for Shell).”
Corvette forum member, Tommy D, made a post which supports the contention that knock retard engine management is not as intrusive on the LS3—“Remember that torque management cannot be tuned out on launch and is not as intrusive on the later C6s.” http://forums.corvetteforum.com/c6-t...post1577287695
On page 6 of “C6 Naked and Exposed – The Sequal; Finally . . . We Drive It!!!," GMPT engineer Jordan Lee states, “When you bump the compression, you need better combustion efficiency, so you're less prone to knock (underline my emphasis); but if you do get knock; you need a control system which can react very quickly so that it’s unobtrusive to the driver.” http://www.corvetteactioncenter.com/...5/sequel6.html
On page 5 of “Ruthless Pursuit of Power: 2008 Edition,” Hib Halverson had this to say about LS3 combustion quality: http://www.corvetteactioncenter.com/...ls3_page5.html “The best combustion quality occurs when the air fuel mixture in the chamber is distributed uniformly, or is “homogenous”, throughout the chamber. The process of becoming homogenous, or as close to it as possible, occurs in the latter stage of the intake valve event and continues once the valve is closed and the piston starts upward. Not only does the upward piston movement compress the air-fuel mix but it also causes it to swirl and tumble and that further mixes it up making it more homogenous. The LS2/LS6 chamber had great swirl but not very good tumble. The air fuel mix needs to be doing both if the goal is homogeneity right when the spark comes.” A bulge added to LS3’s combustion chamber caused the mixture to tumble as well as lowering the compression ratio.
Combustion quality along with a lower compression ratio allows LS3 engines to spend less time in “knock retard” than LS2. This is why LS3, in combination with a somewhat more efficient drivetrain, shows better numbers on many chassis dynos than an LS2 engine with only 20 less horsepower.
Anthony @ LGMotorsports did a back-to-back comparison of a LS2 Corvette, LS3 Camaro and a 5.0 Mustang. Here it is: http://forums.corvetteforum.com/c6-t...post1576411472
LS3 Camaro Max power was 374.35 RWHP; LS2 Corvette was 358.99 RWHP. Difference is 15.36 HP. Camaro LS3 Certified HP is 426; LS2 Certified HP should have been 411. That is a 15 HP difference. I believe a back-to-back comparison means all dyno runs were done at the same time. It looks like LS2 was on the right timing table.
LG Motorsports’ back-to-back comparison shows that the power differential between LS2 and LS3 is greater in midrange rather than at peak power rpm levels. LS3 surpasses the 15 horsepower difference at about 3500 rpm . This continues until peak power is reached at 5900 and 6000 rpm where there is a 15 horsepower difference. The chart also seems to show LS3 losing power more rapidly than LS2 after peak power levels are reached. Projecting LS3’s power curve to 6600 rpm, it looks like LS2 and LS3 power levels will be practically the same. But don’t forget, this is for the 426 HP LS3, not the 430 HP Corvette LS3.
GM’s Corvette power and torque chart shows that, unlike LG Motorsports, the greatest power differential between LS2 and LS3 is reached at peak levels. Scroll down the following link to see the GM chart (http://www.corvetteactioncenter.com/...ls3_page6.html). This chart shows that LS2/LS3 power and torque are nearly the same until about 3500 rpm, where LS3 starts climbing at a faster rate. LS3 power and torque change their angle of ascent, whereas, LS2 continues rising at a steady rate. LS3 acts more like an LS6, so “coming-on-the-cam” is a noticeable sensation.
How LS2 made 20+ HP over ’01 LS6 and LS3 made 20 HP more than LS2
Dividing ’01 LS6’s 385 horsepower by its 346 cubic-inches results in 1.1127 HP per cubic-inch. Multiplying that figure by LS2’s 364 cubic-inches results in 405 HP. Both engines use the same cylinder heads and camshaft, but LS2 has a power-increasing higher compression ratio (10.9:1 advertised – 10.87:1 actual) than LS6 (10.5:1).
LS2 has a single catalytic converter mounted right after each exhaust manifold rather than the close-coupled converters—known as pups—that were combined with the under-car converters on the ’01 LS6. Having one converter on each side reduced back pressure by 2-inches of mercury (16%), which on its own is worth about five horsepower. Along with exhaust manifolds that flow 4% better and exhaust pipes with smoother bends, LS2 benefits by having longitudinally-mounted mufflers with larger internal volume resulting in 10% less restriction than the transverse mufflers with four, 90-degree tube bends that were mounted on all C5 Corvettes. These improvements resulted in a total of 20% less back pressure in the exhaust system.
A redesigned induction system (air box and duct) resulted in 31% better airflow. Most of this increase was the result of C6 Corvettes becoming both front-breathers, air entering through the grill, and bottom-breathers, air entering from the bottom of the car—split 60% front; 40% bottom. Base C5 Corvettes were bottom-breathers only, but the Z06 LS6 had additional air ducted directly to the air-filter box from openings in the front fascia—C6 air flow was an improvement over the Z06. LS2 uses the same mass-air-flow sensor (MAF) as the '02 to '04 LS6, but with the honey-cell flow straightener found in the '01 LS6. Throttle body size went from 76-mm on the LS6 to 90-mm on LS2. Fuel injector capacity increased to 32.5 lb/hr. (4.1 g/sec.) from LS6's 28.5 lb/hr. (3.6 g/sec.).
LS2’s intake manifold was produced using the vibration welded process. It is glass-filled and made out of Nylon 6 rather than Nylon 66, which was used in LS6’s lost-core-process manifolds. The bell-mouth is larger and runner geometry has been optimized for a six-liter engine. The combined result of all intake/induction system improvements is an air flow increase of 15%.
Vibration welding has resulted in seams that allow crosstalk—air passing between runners—which is detrimental to smooth air flow and results in some lost power. GM went back to the lost-core process for the LS3 engine but used Nylon 6. John Rydzewski, Assistant Chief Engineer for Small Block Passenger Engines: “A vibration-welded intake has different shells. One port can be a combination of an upper portion and a bottom portion with the runners welded together on the side. It’s a pretty good seam, but there might be a little crosstalk (port-to-port leakage) which can rob you of some power. We had seen that in some applications, so we went to a lost-core intake (on LS3).” http://www.corvetteactioncenter.com/...ls3_page6.html Vibration welding was also used in the production of LS7 intake manifolds; however, at some point the seams were sealed to prevent crosstalk. I doubt that sealing was ever used on LS2 intakes.
LS2’s pistons have a true flat-top design with all three rings having lower tension than LS1 and LS6 rings. Lower tension reduces friction to free up horsepower. The pistons also have full floating wrist pins that help reduce the piston slap noise that’s common on Generation III engines (LS1, LS6). Gen IV engine blocks (LS2, LS3) have siamesed cylinder bores, meaning that a water slot between bores is unnecessary for adequate cooling and that all bores have a solid, uninterrupted connection. This resulted in a stronger block that is less prone to heat distortion in the cylinders. Less bore distortion means less friction and pumping losses.
Both intake and exhaust airflow are better on LS2 Corvettes than the 2001 LS6. LS2 uses the same cam and heads as the ’01 Z06. With a higher compression ratio, 18 more cubic-inches, induction/intake and exhaust flow better than 2002 to 2004 LS6 engines and various internal modifications that decreased friction and pumping losses, LS2 should have been rated at the 406 or 407 SAE net horsepower that Tony Holloway told me LS2 engines produce. In applications using the LS6 385-horse cam, torque equals horsepower, so LS2 torque should match its horsepower rating.
LS2 never received an official certified rating under the new, for model year 2006, SAE J1349 procedures. But GM, knowing that the new protocol was coming, rated LS2 using the new methods long before the engine received its official 400 horsepower rating. Under SAE certified protocol, LS2 rated between 410 and 415 horsepower. If the new rating system had been ready for the 2005 model year, LS2 would NOT have been rated at 400 horsepower.
The 2002 version of LS6 and 2008 LS3 made 20 horsepower more than their predecessors. Both engines used the same cam intake profiles, but LS3’s exhaust profile is the same that was used in the ’01 LS6 and LS2 cams. Along with more aggressive cams, power gains were derived from exhaust back pressure reductions on the '02 LS6 and better flowing heads on LS3.
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The following six paragraphs were taken from an article titled 2002 LS6 Engine – The Ruthless Pursuit of Power: The Sequel by Hib Halverson, from the January, 2002 issue of GM High-Tech Performance magazine: http://www.gmhightechperformance.com...e/viewall.html
According to LS6 camshaft engineer, Jim Hicks, in comparing the ’01 LS6 cam to the ’02 cam: “You can do a direct A/B comparison and there’s an easy 8-10 HP there, whether you change the back pressure or not. There are other changes in the ’02 package—exhaust system and induction system—which increase the power more. The overall power increased about 20 HP and the cam was half of it. Again, that’s because it’s a short-duration design with low overlap so it’s not really affected that much by back pressure.”
Corvette Chief Engineer, Dave Hill said, “We never set out to obsolete the 2001 LS6. The horsepower increase was possible only after we completed a lengthy development of a new catalyst. I want to set the record straight: the 2001 was the best Z06 we could possibly make and 2002 is better because new catalyst technology let us get the back pressure down, increase the breathing and make that power increase.”
Assistant Chief Engineer for Gen III Passenger Car Engines, John Juriga, added, “In 2000 we had to meet the LEV standard here in California, so we added close-coupled converters up front on the California package, our ‘pups’ as we call ‘em. In 2001 we carried those pups across the board, including on the LS6. Even while we were implementing that, we were working on a design that would eliminate those pups. This reduced back pressure by two inches of mercury. On its own, that was worth about 5 HP. That seems not much, but if you reduce back pressure by even small amounts, you can make a bigger gain with improvements on the induction side, especially with the cam.”
More airflow from the new cam and less back-pressure from the new cats drove some other improvements on the induction side. For MY02, LS6 gets a new air filter assembly. It’s similar to the ’01 unit in that it has an additional air intake opening on its cover, but the extra opening is larger. GM also did what GMHTP readers have been doing for years with MAFs--remove the air flow straightener screen. This allowed for a less restrictive path through the sensor.
There were no changes to either the LS6’s intake manifold or its cylinder heads. John Juriga: “The intake manifold was already pretty darn good. We designed it to handle additional flow rates and not require retool the very next year because composite intakes are very expensive to retool and develop. We made sure it would flow more air than we needed in the first year. The same was true with the heads.”
A change in engine air flow significant enough to provide 20 more horsepower also demanded a small change in the engine’s fuel and spark curves. This was done with slight changes in the PCM calibration. There was no change in injectors or fuel pressure.
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Low hanging fruit had already been picked for the LS2 engine to come up with 20+ more horsepower than the 385-HP LS6, so LS3 needed a significant upgrade for an equal increase in power. LS3 had no changes in the exhaust system after the cylinder head exhaust ports and there wasn't as great a difference on the induction side before air entered the intake manifold. LS3’s intake manifold was again made using the lost-core process and flowed 2-3% better than the LS2 intake. To add 20 more horses, there had to be a major upgrade in the cylinder heads along with the new cam. LS3 did not have the advantage of eighteen more cubic-inches (5.2% more than LS6) and the higher compression ratio that LS2 had over the LS6. LS3 was only twelve cubic-inches or 3.3% larger than LS2 and its compression dropped from LS2’s 10.87:1 to 10.7:1.
A Corvette Action Center article titled Ruthless Pursuit of Power: 2008 Edition by Hib Halverson http://www.corvetteactioncenter.com/...ls3_page1.html describes the improvements that increased LS3 power:
Assistant Chief Engineer for Small Block Passenger Engines, John Rydzewski, talks about improvements in the intake manifold: “We also reshaped it for better flow. Yoon Lee, who’s been on the program for a few years, did the development. Compared to LS2, he reduced restriction by 2-3% at 13.5mm lift. It’s just a smoother path, right down to the head.”
Compared to LS2/LS6 cylinder heads, LS3 heads flow much better. According to Lou Oniga, Design Responsibility Engineer (DRE) for Small-Block Cylinder Heads, “The flow numbers are (average) 17% improvement on the intake and 6.2% on the exhaust.”
LS3's camshaft was improved with a 405-HP, LS6 intake lobe profile--exhaust lobe profile from the 385-HP LS6/LS2 cam was retained.
LS3 fuel injectors come from LS7 and flow 5-gram/sec.--LS2 injectors flow 4.1-gram/sec. The throttle body carries over from the LS2. There are no functional changes to the positive crankcase ventilation (PCV) system. The induction system ahead of the throttle body is from the Z06, but with some quarter-wave tuners added to attenuate certain frequencies of intake noise. Overall, induction/intake restriction has been reduced by 10% (Corvette Quarterly, Fall 2007, page 50). The exhaust manifolds are similar to the units introduced in 2005 on LS2, but have a slight change in each exhaust runner where it bolts to the head to match the revised exhaust port exits. Exhaust pipes after the manifold are the same as the LS2, but when the NPP option is included, a flap in each muffler opens allowing exhaust gases to flow more freely...adding 6-horsepower.
There are improvements in the LS3 block: Main bearing webs are about 20% stronger and windows, which enhance “bay-to-bay breathing” in the interest of oil control and reduced parasitic loss, have been somewhat enlarged. LS3's ring package has once again been changed: The top two compression rings have the same tension as LS2 rings; the bottom, oil ring tension was increased. All rings have a .25-degree increase in grove tilt. Increased grove tilt and oil ring tension improved oil control, but more tension adds friction, which is a drag on power.
Summary
LS2 vs ’01 LS6 (http://www.corvetteactioncenter.com/...5/sequel5.html) (http://www.gmhightechperformance.com..._look_feature/) (Corvette: Sports Car Super Star by the Auto Editors of Consumer Guide, 2005, Publications International, Ltd., page 391) (The Complete Book of Corvette: Every Model Since 1953 by Mike Mueller, 2006, Motorbooks – MBI Publishing Company, pages 315 & 328)
LS2 Exhaust System – New exhaust manifold is capable of 4% better flow; back pressure reduced by 2-inches of mercury (16%) with a single catalytic converter attached to exhaust manifolds rather than close-coupled pup-cats and under-car converters; smoother exhaust-pipe bends; 10% less back pressure with the elimination of four, 90-degree tube bends at mufflers and less restrictive larger internal volume mufflers. In total, the reduction in exhaust back pressure is 20% over the 2001 base system.*
LS2 Intake System – Significant improvement was made because C6 Corvettes became both front- and bottom-breathers. Intake manifold: runner geometry optimized for six-liter displacement; larger bell-mouth; crosstalk causes slight power loss. Throttle-body size increased from 76-mm to 90-mm; induction system (air box and duct) redesigned for lower restriction—31% lower restriction than LS1 induction system.* Overall, intake/induction system airflow has been improved by 15%.
*Note: Beginning with the 2001 production year, LS1 and LS6 engines used the same intake and exhaust manifolds, MAF sensor, and throttle body. These improvements were worth an added ten horsepower to the LS1. For model-year 2000, the addition of pup-cats to California Corvettes resulted in a loss of five horsepower, which means these cars actually made an unadvertised 340 horsepower. The same power reduction would have happened to all 2001, LS1 Corvettes if it hadn’t been for the intake and exhaust upgrades. Chevy never publicized the California power loss and didn't rerate the engine until 2001 (350 HP).
Cylinder heads and cam – Heads are same as 2001 to 2004 LS6; cam is same as 2001 LS6
Engine – Compression ratio increased from 10.5:1 to 10.87:1; displacement increased by eighteen cubic-inches or 5.2%; lower tension piston rings free up horsepower; siamesed bores result in a stronger block and cylinders with less bore distortion, friction and pumping losses.
LS3 vs LS2
LS3 Exhaust System – no change from LS2
LS3 Intake System – Intake manifold restriction reduced by 2-3% and made with lost-core method—no lost power; throttle-body same as LS2; induction system same as Z06, but with quarter-wave tuners; overall induction/intake restriction reduced by 10%.
Cylinder heads and cam – Significant cylinder head upgrade with average intake flow increased by 17% and exhaust increased by 6.2%; cam intake profile same as ’02 LS6, exhaust profile same as LS2.
Engine – Compression ratio dropped from 10.87:1 to 10.7:1; displacement increased by twelve cubic-inches or 3.3%; reduced parasitic loss from increased bay-to-bay breathing; a .25-degree increase in piston-ring grove tilt and higher-tension oil rings resulted better bore sealing and oil control, but increased power-robbing friction.
LS2 improvements resulted in a 21 or 22 horsepower increase over the 385-HP LS6 and LS3 improvements resulted in a 20 horsepower increase over LS2. Compared to LS2, LS3 had no increase in exhaust flow after exhaust gases left the heads and induction/intake flow restriction was reduced by 10%. LS3’s cam was not as significant an improvement as the 405-HP LS6 cam was over the 385-HP version. The 405-HP LS6 cam gained from 8 to 10 HP, so in my opinion, LS3’s cam gained somewhat less. To get another 11-14 horses, LS3 needed a major flow increase from its heads (17% intake - 6.2% exhaust), especially considering that LS3's compression dropped compared to LS2 and it had 36.5% less increase in cylinder volume in comparison to LS2’s increase over LS6. LS2's largest power gains came from increases in compression and cubic-inches, but significant air-flow upgrades--15% on the intake side and 20% on exhaust--were the drivers of more power and torque at both low and high rpm levels without using a bigger cam.
During engine development, Corvette's Chief Engineer and Vehicle Line Executive, Dave Hill, wanted LS2 power to be where the Z06 LS6 was (405 HP) without the premium hardware (longer, hollow-stem valves with potassium-sodium filled exhaust stems), although LS2 did get the stiffer '02 - '04 LS6 valve springs for high rpm stability. I bet he was satisfied with the outcome. GMPT’s Executive Director of Engine Engineering, Sam Winegarden: “Chief engineer Dave Hill said he would really like to take all standard Corvettes to where the Z06 was, and we said that jived with where we saw our competitors, from an engine perspective, going in terms of horsepower. We continually benchmark our engines against our competitors and look at the trends.” (Corvette C6 by Phil Berg, 2004, Motorbooks International, page 63)
Jim Hall, owner of Corvette Forum vendor, Halltech Systems, LLC (Halltech), started a thread with an interesting post on 4/29/2004 that was ahead-of-the-curve. I was not able to find his original post, but it was quoted in another post: https://www.corvetteforum.com/forums...post1550170810 (The beginning of Jim's thread was deleted. If you look at post 1 and 2, it becomes clear these were not the first two posts of the thread. They were made on 3/19/05, almost a year after the thread was started on 4/29/04, and then renumbered. Sometime after the original thread began, GM expressed great displeasure with a vendor's post on this forum. It could have been this one--my memory of the details has faded with time. Obviously much of the original thread was eliminated, so we only have the following quote from post #9 as evidence of Jim Hall's original post.)
Originally Posted by Jim Hall
The C6 is actually 420+ HP.
Why do I suggest that? Three years ago, I posted a thread on the corvetteforum, with a poll asking how many folks would purchase a C5 Coupe with a LS6 option. There were many interested members.
Some quoted Dave Hill as stating that he would never put the Z06 motor in the Coupe or Convertible.
The C6 is just that and more.
400 HP is ridiculous for the amount of internal changes found in the LS2. It is actually a hot rod Z06 motor in sheeps clothing.
A quick comparison: 2004 Z06 has a smaller throttle body-76mm vs. 90 mm for the 2005 C6. The Z06 has a 5.7 liter motor vs. the 6.0 liter LS2. The intake manifold has been redesigned to accommodate the better flow characteristics of the throttle body, and the heads are also improved from a port configuration standpoint. i.e. a ported LS6 head. The compression ratio was automatically increased with the new swept volume from the additional displacement and Z06 combusion chambers to 10.9:1 vs. 10.5:1. Iridium plugs, and hotter coils mean better combustion.
Bigger fuel injectors than the 2004 Z06 with four hole injectors are rated at 4.1 g/s vs the older 3.67 g/s (both at 400 kilopascal or 58 psi rail pressure)
The Z06 heads being utilized flow 15% more air on the intake side, and 21% more on the exhaust port side. 2.00"/1.55" valves are the same steel valves as the LS1. but the springs are Z06.
The exhaust manifolds flow 4% better than the Z06 exhaust manifold (our dyno testing in 2001 suggested that shorty headers vs. the LS6 headers, showed zero improvement in horsepower or torque, so GM has done some homework here) with the straight through mufflers reducing backpressure 10%, and now no pup cats! Finally. No A.I.R. pump! Bay to bay breathing as in the Gen III Z06, has been a part of the LS1 and LS6 for a few years now.
The cam used is the 2001 Z06 cam, with a .525"/.525" lift (2004 Z06 cam is .555"/.551" and similar duration, so here you can subtract 10 RWHP, for the C6 with the same head port design, but with the increase port flow, the actual loss from a lower lift may be insignificant. We have the present Z06 cams, ready to install as soon as our C6 comes in.
They have also gone back to the lower tension rings found in the 2001 Z06, but without the oil consumption problems, which means less frictional losses. Anodized ring lands, may help strengthen the lands, but not from forced induction senarios. I am very disappointed that forged pistons were not used.
GM would have you compare the LS2 to the LS1 to keep the Z06 hot rodders happy, but the truth is out there. The real comparison should be the LS2 vs. the LS6. The LS2 is the new KING of horsepower, no matter how GM spins it.
With all of the above changes to the basic Z06 platform, do they expect anyone to believe that there is only 5 HP LESS than the Z06...???
From a marketing standpoint, it would kill the remaining 2004 Z06 sales, if the new C6 became available with 420 advertised HP.
One more thing. When the Z06 (LS7) motor hits the scene, the 3 valve head design, dry sump, and 427 cid will bump the horsepower to 535. GM will claim much less on paper.
Jim Hall
[Modified by Jim Hall, 7:53 PM 4/29/2004]
At the upscale Detroit Opera House, on January 4, 2004, GM held a snazzy, invitation only event for the unveiling of the brand new C6 Corvette with Rick Wagoner, GM Chairman and CEO, as the main speaker. Perhaps Jim Hall was at this event, or some other information session, learning about what makes Corvette’s new, LS2 engine tick. Jim was obviously well informed, because he was 100% correct with his 420+ horsepower prediction with a caveat. He stated, “…you can subtract 10 RWHP…” for the cam, which results in the same 410+ horsepower that preproduction LS2s rated under the imminent, certified protocol.
Power Progression: LS6 – LS2 – LS3
LS6 heads were originally designed with more than enough air flow to accommodate a 405 horsepower LS6 engine. So, identical LS2 heads (243 castings) already had enough air flow to feed 406 or 407 HP as measured with the original SAE J1349 rating procedures used by all U.S. auto manufacturers from 1972 through 2005. When Chevy rated the preproduction LS2 with what became the new, for model year 2006, SAE certified protocol, it measured between 410 and 415 HP. All GM engines that were rated under both standards had higher horsepower numbers with the new certified protocol.
A redesigned C6 platform allowed for better induction and exhaust air flow than was possible with the C5 platform, including the C5 Z06. LS2’s increased air flow, compression and cubic inches resulted in a stronger engine than the 2002 to 2004, 405-HP LS6.
Two sets of heads were developed for the LS7 engine. The first heads were ultimately rejected because they couldn’t produce the desired power. After some additional work, these heads were used on the LS3. LS3’s fuel injectors and induction system ahead of the throttle body (MAF sensor, air box and duct) also came from the LS7—these parts flowed more fuel and air than necessary, but since they were already inventoried, using them eliminated extra engineering, development, production, and inventory costs. LS3’s throttle body and exhaust system, except for a small change in the manifold to match the head’s reshaped exhaust ports, were from the LS2. Using off-the-shelf parts was a cost effective way to reach 430 SAE certified horsepower in a normally aspirated, overhead valve, 6.2-liter engine.
Horsepower per cubic inch
SAE net (pre-2006)
2001 LS6 – 1.1127 (385/346)
2002 LS6 – 1.1705 (405/346)
2005 LS2 – 1.1154 (406/364)
SAE certified (post-2005)
2005 LS2 – 1.1291 (411/364)
2008 LS3 – 1.1436 (430/376)
Increasing an engine’s cylinder volume will increase torque, however, without corresponding increases in air flow and/or compression, power per cubic-inch will decrease. LS2 and LS3 engines had significant increases in air flow. LS2’s increased compression plus improved intake and exhaust flow were spread over a 5.2% increase in cylinder volume and LS3’s improved heads and cam along with better intake flow were spread over a 3.3% cylinder volume increase. Higher volume increases require correspondingly higher air-flow rates to maintain equal power levels per cubic-inch of total cylinder volume. This explains why LS3’s horsepower per cubic-inch is greater than LS2’s (LS2’s cylinder volume increase was 36.5 % greater than LS3’s) and why the 2002 LS6 had a significant increase in power per cubic-inch over the 2001 LS6 (no change in cylinder volume).
____________
For more information on LS2 Corvette evaluations, comparisons and history, see the Corvette Forum thread titled LS2 Certified Horsepower?—For LS2 Guys at the following address: http://forums.corvetteforum.com/c6-c...-ls2-guys.html Information that you just read in this post is included in the thread.
Last edited by Marina Blue; 05-17-2015 at 06:12 PM. Reason: Add Jim Hall's Quote
01-17-2014, 11:34 PM
#10
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What? Again ? Still ? After all these years?
As long as you're quoting Jim, you should quote his comments regarding LS3 vs LS2.
As long as you're quoting Jim, you should quote his comments regarding LS3 vs LS2.
01-18-2014, 12:58 PM
#13
Burning Brakes
Thread Starter
Yes, after all these years, I felt my original thread needed a lift because of continued interest. It was brought back to life in 2012. At that point I followed progress by tracking the number of views. Over a 15 month time span there were 9,538 views (12,222 on 10/21/2012 to 21,760 today) that were increasing at a steady rate. That’s a pretty impressive number considering the thread was never in view on the front page, but hidden deep in the Forum’s archives. All that activity, while out-of-sight, warranted its return to the front page. It is now in the sticky section as well as listed in The Official C6 Mega Thread. I included a link at the bottom of post #1 because it was not yet a sticky when I started this thread.
Hope you found the information interesting.
PS Jim's quotes were used to illustrate the seat-of-the-pants feel of the LS2 compared to its performance, not as a comparison to LS3. The LS3 is faster, and feels stronger, but the difference is not night and day, just as Jim's track performance with his LS2 and LS3 were not significantly different.