TedH

Have you ever wondered why it is that Chevy High Performance, Hot Rod and others can easily build 350hp engines? There seems to be this 'standard recipe' that if you follow it (Vortec heads, Xtreme energy cam, headers, Performer RPM, Holley 750cfm, flat top pistons, etc.) the result is predictable. I followed a very similar approach and I have less-than-spectacular results. The difference: DART Iron Eagle 180cc heads (72cc chambers), Crane Energizer 272H duration (.454/.454 lift, 216 @ .050"), Performer intake (3701), Q-jet carb. My results are in my signature. Either I have a bad cam, heads or carb or I'm losing incredible amounts of power between the flywheel and the rear tires: 222.5rwhp and 288.4rwtq.

As far as this engine goes, I'm done with it. Too expensive to keep chasing that elusive '350hp/400tq (flywheel) dream'.


[Modified by TedH, 1:35 PM 7/14/2003]

jrzvette

Probably because most magazines get parts, tech advice and assistance free (or at very low cost) for using the names of the suppliers.

TedH

This will probably be my last rebuild. I can't afford it. :cry It really is embarrasing to do this work and see the (dissappointing) results.

The options available via reputable builders are much greater than even just a few years ago and results/performance are verified before the built engines are shipped.

Just feeling a little remorse here :mad :cuss

68shark

I wonder if the "350hp" claim is based on engine running bare of accessories and with the usual "dyno exhaust" rather than street equipment on an engine dyno. If so, a world of difference between that and rear wheel horsepower. 350 on the old "gross" basis, like 6T9L46 (for example) is probably equal to around 275hp or so on today's "net" ratings, which would produce readings like yours at the tires. You may be a bit low, but not much. You probably need to "fine tune" your carb and timing to ensure everything is optimized for your setup then run it again. I've dyno'd my car twice, the second time after having a real good mechanic (meaning "not me") set my carb, including changing metering rods. Found over 20rwhp that way!

TedH

Assuming 20% losses from flywheel to rear tires, my rearwheel performance of:

222.5rwhp
288.4rwtq

translates to flywheel (net) performance in the neighborhood of:

278 SAE net HP
361 SAE net Torque

I suppose I should be happy with this performance as it would be close to the performance of some of the late 80's C4's. I still can't help beating myself up about the results :boxing. I suppose that stepping up to an Xtreme Energy cam would help some but I'd expect a penalty given the exhaust flow characteristics of the DARTS favor a single-pattern cam (at least that is what my tuner told me).

Brettmc

Heads, cam, compression makes ALL the difference in the world.

Brett :thumbs:

68shark

Ted, just for comparison purposes, I have a 327 with the stock "double hump" heads, 2.02/1.60 valves, Xtreme Energy 262 cam, hyper. flat tops (approx 10 to 1), stock carb/intake/exhaust manifolds and pulled numbers virtually the same as yours (229rwhp/277rwtq). Your 350, by comparison, has better flowing heads/exhaust and larger displacement. Would think you are at the "finetune" stage to make more power.

TedH

I suspect I am running slightly above or at 9:1 compression with the 72cc heads. The pistons were rated at about 8.64 with 76cc heads (I had the '882' 76cc heads before the DART heads). Am wondering if I lost some of my torque moving up to headers. I suppose I can second-guess myself forever on this combination but I don't want to start swapping parts to find out; too expensive.

I've been in tuner mode for quite a while. The q-jet carb is optimized as is the ignition curve. The only mods that I would even consider making involve an ignition module or perhaps swap to an open-element K&N air cleaner. Beyond that we're talking $$$ (port the heads, swap XE cam, remove/replace mufflers).


[Modified by TedH, 2:06 PM 7/15/2003]

fauxrs

You are probably right at 9.0:1. I am going to assume you didnt deck the block and therefore the piston sits down in the hole reducing 'squish' I would say the Cam is your biggest problem 216@050 is rather 'pooch' for a small block - even a factory L82 has 222 @ 050. I dont know the flow rates of the iron Eagle heads so cant make any intelligent comments regarding that. however I can say that the Vortech heads would almost certainly be an improvement.

I would keep chasing the elusive tune - but likelyhood is you are near what you will see out of that engine (based on your previous comments)

zwede

I think you found out the hard way that magazine articles are hype and lies. They get paid to show manufacturer supplied parts in a good light.

Horsepower TV built a smallblock and put it on a engine dyno and were bragging that they got over 450 hp. In a later episode they installed that same engine in a 2nd gen Camaro with a 4-speed. The dynojet showed 330 rwhp. I think the dynojet was honest (although you can fool the dynojet also, see below), and the engine dyno was WAY optimistic.

So don't think those 400 hp or whatever "easy buildups" you read about will have anywhere near that power.

As for dynojets, I did extensive testing with one (approx 150 runs) and found an easy way to show ANY part making 20 rwhp. Just baseline with a heatsoaked engine, install the part while you let the engine cool off, and then make a run. Since the engine is cooler it will make 15-20 hp more acrrross the board. I have an example on my webpage showing this. If you're watching the car shows on TV you can catch them doing this. Just look for the after graph where the whole torque curve is up 15 ft-lbs across the rpm range.

Edit: Here's the page where I did the test. It's on the bottom of the page:

http://www.corvetteforum.net/c3/zwed.../dynotests.htm


[Modified by zwede, 3:30 PM 7/14/2003]

TedH

You know, when you put it like that, I probably am at the limit of that 272H cam. Considering the L82 produced 230 net hp and I'm now at 278 net hp... I don't see boosting performance; I've optimized this combination. Any other improvements will require hard part changes (cam most obvious).

Thanks for helping put things in perspective. :seeya

So, starting from my OEM L48 baseline of 190hp and 280tq at flywheel, I am now at 278hp and 361tq; an increase of 88hp and 81ft lbs. Now it's time to drive the car :auto: , that is, once I fix that pesky fuel leak at the fuel-to-carb fitting... :mad

Fevre

Ted

It is never going to run like that silver one next to it unless you go FI and roller cam.

81' Corvette Guy

Ekkk Gaddds, do that repair from the fuel to carb fitting..my neighbors car went up in a fireball due to a leaky carb with gas on the intake...not pretty! :eek:

TedH

I know. Spoken truthfully.

Maybe, if I get really adventurous and still have the vette in 2005 (when it hits 25), I'll celebrate its 'birthday' and drop that Crane Roller Cam setup (cam, button/plate, lifters, pushrods, springs) and Comp Pro Magnum rockers into it... :cheers:

I just gotta exit 'tuner' mode and enter 'resto' mode; to focus on steering, rear trailing arm 'eye' bushings and inner door rebuild and interior refresh.

:seeya

LemansBlue68

The magazine HP results are corrected to 60'F air inlet temperature and sea level conditions. This is the way the old (pre-'72) factory ratings were done too. They also do not include ANY accessory losses. In fact, I think they even run their water pumps electrically. You are running your car on a chassis dyno with full accessories, full exhaust, full driveline losses, normal underhood air temps. etc. I wouldn't say the magazines lie, but they sure tilt all the test variables to their advantage.

What you've done is not so bad with 288 (est.) hp at the flywheel. With a little tuning of spark advance and A/F ratio, you could probably still make 300+ hp at the flywheel as you've targeted. Try a set of headers and get the air intake out of the hot underhood air i.e. cowl induction or cold air inlet tube.

I'm a big believer in some of the engine simulation software. The final estimates aren't necessarily right on, but you can try different combinations of parts and see what the differences are in the output, then keep tweaking until you find the best combo. All it costs is $50-$100 for the software--a lot cheaper than buying the parts, installing them and then finding out that you're disappointed with the combo.

Keep the faith! If Thomas Edison had quit working on the electric lightbulb after his first attempt, we'd be typing at our computers by candlelight! :D

tnt76vette

Chevy HiPerf. Magazine's Aug. 2003 issue had an article called "7 Hot Engine Combos". Their 1st motor built was almost exactly identical to mine in all respects. They dynoed a best of 342HP @5000 RPM, and 403 ft/lbs at 3,400. A Forum Member Desk Dynoed my set up at 345HP @5000 RPM, and 409 ft/lbs, 6 months before the magazine hit the shelves, so I think I am in the ballpark........... :D :D :D

427Hotrod

Magazines are amazing..I know some folks that have been the subjects of articles. Really interesting to hear them talk about "what" they can say with regards to sponsor $$$!!!.

And most folks I know are still laughing at that 911 HP 477 in Car Craft!

But regardless, you should be able to make pretty good power with that combo. Something is out of whack. I've seen stock headed 350's break 400 hp with real mild cams and iron intakes (roundy rounder claimer motors). What is your real comression? My rough guess is 9.1 or so at best? Those are pretty big chambers, and with normal .020 or so deck height and gaskets it would hurt some. An extra point of compression can help.

Did you do any work to the heads? How did ports/bowls look out of the box?


JIM

Time to spend some time trading carbs and stuff off of buddies cars to see what's up. I think you can get all over 275+ RWHP with those parts.

nunus79

At what rpms are the peak hp & torque numbers occurring? It sounds like you tried to build a low-end motor and now expect to see a high-end motor results. High rpm motors will show-off with big horse power numbers. But, for the street, I'd prefer a torquey low-end motor. Does your dyno torque curve start close to 250 ftlbs at 2000 rpm and peak in the hi-3000s?

If what I said is not applicable to your setup and you want to figure out what is going on, do a cranking compression test. If you are in the 140-160 psi range, you are too low compression. Ideal is in the 180-220 range.

Head gasket thickness plays a major role in compression. Did you use steel shim gaskets?

MotorHead

Believe it or not you would be very close to 350 HP on an engine dyno if not bang on, subtract 35 - 40 % from 350 HP and you get the the rear wheel HP. If you don't belive me then I have the numbers from the early 70's of both small blocks and big blocks gross and net HP at work, someone here has them too. The big blocks are even worse in the loss department approaching 50% :eek:

This is the problem with buying crate engines and rebuilt engines, they will quote engine dyno numbers and most of the time they are guesses anyway ( takes time and cost money to set one up ) . I have seen several ZZ4's on the chassis dyno and they come in at 240 - 260 HP out of the box on a chassis dyno and I believe they were set up on the engine dyno with a few accessories( so closer to net HP ) I know some of you guys with zz4's are getting more power but that is what I have seen with my own eyes.

If you can get 300 HP at the rear wheels from a SBC you have a real sreamer :D

BSeery

Hey there Ted, don't feel bad. I bought a 355 HP crate motor and installed it in my car.

I only got 218 HP to the rear wheels. At that time I had the stock single pipe exhaust and the tuning was for emissions and not HP, but it shows that you can loose a lot between tuning and driveline loss.

My goal is to get 300 HP to the rear wheels. I now have dual exhaust and headers and will be doing a fuel injection install to take care of any tuning issues.

Even the GM rated motors can be less than power full if all is not right.