Horsepower ratings

[Mark E.]

Re: Horsepower ratings

The advertised CR dropped from 11:1 to 9:1 form '71 and remained unchanged for '72. Internally the '71 and '72 LT-1s are identical, so the 20 HP drop in net '72 rating was had to be due to "external factors" like the vehicle induction and exhaust systems and changes to the spark advance map to meet emission requirements.
Duke

Makes sense. Same engine internals; different spark advance and fuel mix.

[Duke W.]

Re: Horsepower ratings

As I'm reading this very informative thread...I can't help chuckling a little. I have a '72 and while it's a really nice car...Let's face it...It ain't no road burner. I once toyed with the idea of having the original engine rebuilt to 1970 specs...but, I already have way more invested in this car than my estate will ever get for it...and besides, I way too old to worry about "burning up the road."

If you set up the spark advance map to something like the 365/375 HP 327s, you will think it's an entirely different engine, and it's easy to do. Max centrifugal is 22 @ 2300, which is fine. Just set total WOT advance at 38-40 at something over 2300. Convert to full time vacuum advance and install a B28 VAC in place of the OE 201 15, then go through the idle speed/mixture adjustment procedure for pre-emission engines. The improvement in power across the entire rev range and lower fuel consumption will be obvious.

All the whys and wherefores are in my San Diego national convention tuning seminar, which is on the Web.

Of course, someone may have already improved the spark advance map in the past, so the first thing to do is test with a dial back timing light to set what is actually is.

Duke

[Dan D.]

Re: Horsepower ratings

Thank you for the information. I've spent my whole life around the auto industry...it's obvious that you know what you're talking about.

Dan

[Mike F.]

Re: Horsepower ratings

My 70 L-46 made 341hp/387tq (Gross on engine dyno) and when installed in the car with M-21, PS, PB, OEM exhaust manifolds and 2 1/2 under car exhaust it made 244hp/305tq (RWHP on Dynojet).

[Mark E.]

Re: Horsepower ratings

My 70 L-46 made 341hp/387tq (Gross on engine dyno) and when installed in the car with M-21, PS, PB, OEM exhaust manifolds and 2 1/2 under car exhaust it made 244hp/305tq (RWHP on Dynojet).

Mike, where did have your car "dynoed"? We each live in north Texas, and I'm interested in having that done.

[Mike F.]

Re: Horsepower ratings

Mike, where did have your car "dynoed"? We each live in north Texas, and I'm interested in having that done.

Pittsburgh...lol

This was done before I moved to Texas.

[Duke W.]

Re: Horsepower ratings

My 70 L-46 made 341hp/387tq (Gross on engine dyno) and when installed in the car with M-21, PS, PB, OEM exhaust manifolds and 2 1/2 under car exhaust it made 244hp/305tq (RWHP on Dynojet).

Typically STD, "standard temperature/pressure", is used to correct lab dyno observed results and "SAE correction" is used to correct chassis dyno results. Unless this context is known, it's an apples to oranges comparison. Can you state what type of correction, if any, was used for your reported results?

[Duke W.]

Re: Horsepower ratings

Mike, where did have your car "dynoed"? We each live in north Texas, and I'm interested in having that done.

Go to www.dynojet.com You can search for dynos via zip code also download the free "Winpep" software. Develop a test plan (send me an email if you want a template) and discuss it with the shop before you commit. Determine how you can take the individual test file with you. They are very small. If the computer has email, that will work, or whatever I/O device it has...CD, thumb drive, etc. Now you load those test file onto your computer and use the Winpep software to manipulate the data, show different graphs, use different correction factors, etc. Also, please start the runs at no more than 1500. For some reason dyno operators don't like to start this low, but it will do more harm, and this data is needed to understand the full across the range performance characteristics. Also agree on the maximum test RPM. Don't let the guy stop the test just because the power appears to have peaked.

[Mike F.]

Re: Horsepower ratings

Typically STD, "standard temperature/pressure", is used to correct lab dyno observed results and "SAE correction" is used to correct chassis dyno results. Unless this context is known, it's an apples to oranges comparison. Can you state what type of correction, if any, was used for your reported results?

New 1.pdf
New 2.pdf
New 3.pdf

[Duke W.]

Re: Horsepower ratings

Thanks for posting the data. The torque curve is tough to see, but it looks like it makes 90 percent of peak at 2000, which is excellent and better than I thought a L-46 would do. Massaging the heads would have added about ten percent more power in the upper rev range. The lab dyno test exceeded the advertised gross torque rating, so I assume it was done with headers. Is that correct?

[Mike F.]

Re: Horsepower ratings

Thanks for posting the data. The torque curve is tough to see, but it looks like it makes 90 percent of peak at 2000, which is excellent and better than I thought a L-46 would do. Massaging the heads would have added about ten percent more power in the upper rev range. The lab dyno test exceeded the advertised gross torque rating, so I assume it was done with headers. Is that correct?

Yes, the lab dyno was done with headers and the heads were massaged.

[William F.]

Re: Horsepower ratings

The 396 rated at 375 hp in a chevelle was another one that was under rated. NHRA figured out it was essentially the same as the Corvette 396 rated at 425 hp and used the 425 number for putting these Chevelles in a class.

[William F.]

Re: Horsepower ratings

I always come away form threads on this subject a little confuse. Do I have this right; The "net" horsepower rating used for '72 on are at the flywheel with stock induction system exhausts, engine mounted accessories in place, but NOT rear wheel horsepower??

[Michael W.]

Re: Horsepower ratings

I always come away form threads on this subject a little confuse. Do I have this right; The "net" horsepower rating used for '72 on are at the flywheel with stock induction system exhausts, engine mounted accessories in place, but NOT rear wheel horsepower??

No OEM uses rear wheel horsepower, back then or now.

[William F.]

Re: Horsepower ratings

So, Michael,
on a new car that says has such and such horsepower, that's rear wheel horsepower, like it's calculated with car in it's entirety tied down and run on a chassis dyno? Not just the engine on a stand but with stock exhaust and all accessories installed??