1968-72 Corvette PR

Hi to all.

All of us C3 Corvette knowers know that the 1970 LT1 is rated at 370hp, and that the LS5 of that same year is rated at 390hp.

I believe that the 370hp rating of the LT1 is a factory lie, another case of an engine being underrated by the factory, and that the true hp of the LT1 is closer to 400hp. If this is the case, then the LT1 is probably a bit more powerful than the LS5. Is there any fact to this ? Do any of you know ?

Another thing. Of the 1287 LT1 Corvettes of 1970, only 25 were built with the race-ready ZR1 package. Was the LT1 in the ZR1 any different from the normal LT1 ? Did the ZR1 have a little bit more hp than the normal LT1 ?

Also, did the LT1 have L88 components ?

Wanting to know.

Best regards,


José, from Puerto Rico

Roughrider

The LT-1 in the ZR-1 package was the same engine. The ZR-1 package included other performance goodies...primarily chassis mods compared the standard car.
No way the LT-1 had L88 components...LT-1 was small block...the L88 was a big block. About the only things that could interchange were the oil filters, thermostat and maybe a few sensors. Though the distributors could fit one another they were calibrated differently.

Horsepower ratings were often the subject of subterfuge back then. Not so much that the car makers absolutely lied about them but played games with ratings in other ways. For example, say Chevrolet gave a particular engine a rating of 350 hp at 4000 rpm's, that tells the insurance companies it may not be a super power engine. What they don't say or advertise is the same engine puts out 425 hp at 5500 rpm's (just making numbers up...may not be realistic but simply for example).

That's how Chevrolet got away with rating the L88 at 430hp...it was true for the hp/rpm they advertised. It could actually put out over 500hp at a higher rpm. They simply did that to discourage street drivers from buying the car as it was for dedicated racers. They preferred to sell the 435hp L71 to street guys so gave it a higher hp rating plus a few creature comforts they deleted with the L88 cars.

All kind of reasons why car makers play with advertised hp ratings.

MN-Brent

wiki:
LT-1
Years: 1970–1972
The LT-1 was the ultimate 350 cu in (5.7 L) V8, becoming available in 1970. It used solid lifters, 11:1 compression, a high-performance camshaft, and a 780 CFM Holley four-barrel carburetor on a special aluminum intake with ramhorn exhaust manifolds and a low-restriction exhaust to produce a factory rated 370 hp (276 kW) (the NHRA rated it at 425 hp for classification purposes) and 380 lb·ft (515 N·m). Redline was 6500 rpm but power fell off significantly past 6200 rpm.

The LT-1 was available on the Corvette and Camaro Z28.

Power was down in 1971 to 330 hp (246 kW) and 360 lb·ft (488 N·m) with 9:1 compression, and again in 1972 (the last year of the LT-1, now rated using net, rather than gross, measurement) to 255 hp (190 kW) and 280 lb·ft (380 N·m).

7T1vette

The LT-1 engine was a potent small block machine...but it didn't have the flat/constant torque level that the big block engine had. But, since the BB was heavier, an LT-1 car and a 400hp BB car were probably evenly matched. Some folks liked high-revving cars; some liked raw torque. What you bought depended on what you liked. Oh....the BB engine was a little more than half the option cost of the LT-1. It was more expensive to get that much power out of a small block engine.

Timsride

The LT1 in the 70 Z28 camaro was down 10 HP from the vette. The only difference being the carb on the camaro, if I remember corectly it was a 750 Holley.

Les

The Z28 carb was also 780 cfm. The Z28 had a single crossflow muffler instead of two mufflers like the Vette. I've never seen that identified as the reason for the 360 HP rating but it may have been. I have seen it written that the Vette got the higher rating to keep the Vette as the "top dog", although I don't know for a fact if that's the case.

10caipirinhas

It was over rated IMHO by about 25-30 HP.

Hot Rod did a couple of dyno tests of OEM small block GM, Mopar and Ford engines in a rather long and detailed magazine article not too long ago (within 5-7 years IIRC) and the LT1 was down on HP (it actually produced around 340-350 at the flywheel) whereas the 302 was well over 300. The Ford's were all under rated and produced in excess of their factory ratings due to their excellent flowing cylinder heads.

The article was posted here on this site, and while I did search for it I could no longer find it, even though I read it within the last year. Perhaps someone else will post it.

FWIW the state of tune of each engine will have affected the outcome and any competent tuner could have easily regained probably 10% more in each of these engines with tweaking. This test was just a snapshot in time on a particular day.

Lt1er

As a proud owner of a Lt1 I can tell you that it was over rated at 370 hp. It has been said that factory rating were without ACC attached. So no belts on the front of the motor. The motor was held back by a low lift cam and head technology of the time period for production cars. I have a modern solid cam, higher lift, ported and polished heads....., and balanced motor that puts out a true 400 hp at the crank. It is a vast improvement over the factory "LT1" I have no problem revving it up to 7000 rpm. The best thing you can do for a LT1 is to throw away the cam and springs

SteveG75

Well, if GM underrated the LT-1, what makes you think that they didn't underate the LS-5? So, even if the LT-1 made 400 hp, and I am not saying it did, that what prevents GM from selling an LS-5 that made 420 hp?

z10kl

The Vette had better flowing exhaust manifolds and transistorised ignition.

jb78L-82

As mentioned above, the HP ratings of all engines prior to 1972 were GROSS HP figures versus NET HP ratings beginning in 1972. Gross HP ratings were done on an engine stand, with zero accessories hooked up (no water pump, alternator, power steering pump, AC compressor, and an open exhaust (probably not even ram horns) with no exhaust system at all and were measured at the flywheel. Net HP ratings include all of the above installed and hooked up as well as any emissions hardware, and a completely stock exhaust system including the pipes, OEM ramhorn manifolds, and mufflers-thus the giant HP drop starting in 1972. A 1971 LT-1 rated at 330 HP Gross is really no different than a 1972 LT-1 rated at 255 HP NET-they are essentially the same engine just rated differently. With these differences in mind, it is not surprising that a genuine 400 HP SB today would feel MUCH more powerful than a LT-1 rated at 370/350/330 Gross HP. A 1970 370 HP LT-1 probably actually made about 310-325 NET HP. Hope that helps!

garage-ghost

I had my 72 on a Mustang Dyno, (stingy with HP); a couple of years ago, just to see if GM did under rate them. The results were 260HP @ 5500 RPM I wouldn’t let them go higher even after they begged, saying “it was still climbing real nice”. I was afraid of breaking something. I have never had it over 5000 so letting them go to 5500 was a real heart stopper.

dmayhew

[QUOTE=1968-72 Corvette PR;1575535448]Hi to all.

LT1 is closer to 400hp. If this is the case, then the LT1 is probably a bit more powerful than the LS5. Is there any fact to this ? Do any of you know ?



If you concede that the LT-1 under rated , then would it not make sense that the LS5 was also underrated?

The 390 HP could have been closer to 425??

I think the HP game was marketing magic

Who cares in the end, If the LS5's and LT-1's were kicking the crap out of mustangs on the street then that is what counted in the real world

Solid LT1

LT-1 SAE tests were supoosedly performed with 30-30 Z28 cam where the real LT-1 cam is a little smaller on the intake (same exhaust.) My wife's LT-1 is only 370HP just like it says on the plate "bone stock" yeah that's the ticket

Gale Banks 80'

Lets keep in mind that the LT-1 is the 70-73 and the LT1 is the 1990-96 Engine. Chev High Performace Magazine did a Test on the two of them in the last 6 months or so. It was wild how the two of them were very close in HP being 20 Years apart. The LT-1 had a bigger Cam but the new LT1 had many modern improvements. They both made about 350 HP at the Flywheel with Dyno Headers.

HamadUP

The Car & Driver magazine tested a LS5 with a TH400 and 3.08 and loaded with many heavy options, it passed the 1/4 mile in 14.2 @ 100.33 MPH, and Motor Trend mag. tested a '70 LT-1 with 4 sp. and 4.11 rear and it passed the 1/4 mile in 14.36 @ 101.69 MPH.

jb78L-82

That would certainly match up with my estimate above of Gross versus net horsepower for a 1970 370 HP LT-1. GM rated that motor with 370 GROSS HP with zero accessories and no exhaust. Add back the accessories with no exhaust 340-350 Gross HP at the flywheel. All accessories with a full stock exhaust about 300-310 NET HP, much less to the rear wheels after drivetrain losses which are greater 40 years ago than today. Again, there really is not much debate on this issue since the 1971 GROSS rated 330 HP LT-1 is the exact same LT-1 as the 1972 255 NET rated LT-1. Same engine, 75 HP difference between the GROSS and NET ratings. Hope that helps!

Also, the 1/4 mile times tell the real story about the actual HP of the 1970/71 LT-1's with a 14.3 sec time with 4.11 gears and a car that weighted about 3,200 lbs or less. Those times along with the weight, and 4.11 gears indicate a true NET HP of probably under 300 HP (more like 290-295 HP). As a comparison, a 78/79 L-82 4 speed with 3.70 gears which is a couple of hundred pounds heavier than the early 70 C3's with a 225 HP NET rated engine (L-82) would do high 14's in the 1/4 mile according to magazine articles at that time.

I think that the 70/71 LT-1's are possibly the best small blocks put in the C3's, but there is a tendency to over exaggerate the actual HP and performance of these SB's versus the many others that were offered over the years. Were they better, most certainly. Is a 71 LT-1 330 HP/350 HP, (not the 370 HP) much faster than the 74 L-82 4 speed rated at 250 HP, NO.

stuartc53

I have an original 70 LT1 that came with Lunati cam with 502 lift when I bought it. I was gonna change it back to make it original, but after reading your post, I am thinking twice. What cam do you have in your LT1? Thank you

Easy Mike

Okay.

No. The LT-1 is a small block. The L-88 is a big block.

Buy a copy.


This is also good.

Mike Ward

More dead in the grave threads being dug up for no apparent reason?