silverja

I was curious about our C4 horsepower and torque ratings. Our models are based on bhp numbers while earlier generations used gross numbers (I believe at the flywheel). What would a 240 HP and 340 lb-ft. torque be if rated by the older fashion (ie net numbers)? I read in Corvette magazine that the 92 C4's with the LT1 engines (rated at 300 HP) had more horsepower than the original 1970 LT1's that were rated at 370 gross hp.

Thanks in advance.

vader86

Its difficult to say since todays engines are always rated in Net power with the accessories on the motor. Todays engines are also more accurately rated than what came out in the old days, where most were underrated for insurance purposes.

I dont believe the accessories on the LT1 sucked out 70hp compared to the LT-1s. Assuming that the LT-1 was accurately rated back then.

rocco16

I believe it was more than just accessories, '86.
I seem to recall that the gross method was taken sans air cleaner and with open exhausts, whereas the net method (while it was taken at the flywheel, too) had ALL the standard stuff in place, including cats, mufflers, and full tailpipes.

Larry
code5coupe

mean8t

The old one was the LT-1. They stoped gross numbers in 71. So the 71 LT-1 was rated at 330hp at 5600 rpm and 360ft-lbs at 4000rpm, 72 LT-1's were rated at 255hp and 280 ft-lbs at the same rpm. The drop from the 70 LT-1 to the 71 LT-1 was due to the drop in compression from 11:1 to 9:1.

bogus

Here is the score....

rocco16 is on target, but it gets even wackier than that - they didn't even use a waterpump!!! SAE Gross numbers were lies, outright lies.

There is an equation out there that converts Gross to Net, I just don't remember it.

Very few engines of the muscle car era were accurately reported... short of the 426 hemi, the 427 Side Oiler and the Mark IV 427, the rest were jokes.

Some were accurate, but the rest were over inflated. Seriously.

My exgf has a 71 stang, POS. It has a 302 2bbl, 210 Gross hp, in 1972, the same motor? 136. I rest my case.

silverja

I found a web site that claims today's "crate" engines are still using gross horsepower numbers (inflated versus net ratings). I never gave much thought about this, but have noticed GM crate engines appear to have more horsepower than the ones from the factory in new Corvettes.

vader86

No, the GM numbers are NET numbers, but usually they are rated at the flywheel with exhaust headers on the car. Some sellers dont tell you that much.

Its correct that current NET ratings are not just with accessories, but with everything else thats in production models. I shouldve added that.

mean8t

In 92 Corvette Fever did some dyno runs on a L88 motor with the factory exhaust and with headers. Now mind you that the factory rated these beasts and 430 hp 5 less than the L-89 427. The test read 514 hp at 6200rpm and 513 ft-lbs at 4200 rpm. As for headers they gained about 100 hp. If that was uderrated then the ZL-1 is an out right lie. It is rated at the same 430 hp, but had a bigger cam .536/.560 for the L-88 and .560/.600 for the ZL-1, and better flowing heads. I have never seen any accurate dyno tests on one b/c there were only 2 ever built, but it is the fastest vette ever built problably including the 06 Z06.

On an aside, with a decent converter in a TH400 and 4.88:1 gears a ZL-1 powered press car ran 10.89 at 130mph.

VAHROOM

IMHO, you can't ever see an accurate dyno test because there is no such thing. You can get a close measurement but there is no way to make sure the reported number is true.

There are so many dyno types. Dyno numbers are great as long as the cars being compared are run on the same dyno under the same conditions. Even running the same car a few times in a row will give you different numbers each time. That is because air temp, water temp, engine temp, dyno calibrations, etc. all change. Heck I forgot to mention different dyno operators, stuff bolted on the engine, fuel and brands make a difference. I guess my point is, you can test and get one set of numbers, and tell another. BUT that is just my 2¢

C-4 Now

When I had my 68 L-88 [stock except side header exhaust that came with car in passenger seat] ran it at the local road race track. Made a couple of people grumble loudly because car ran stock class. Was a handful on corners Have had and drove a lot of Vettes but that car was a memorable beast no under rating there
Ike

Mr Mojo

General rule of thumb has been 10% loss at the flywheel with all the accessories, so that would put the LT1 rated at 300 to 330. Sounds reasonable to me.

95wht6spd

Yes, but like other have said there is still more to it than accessories for GROSS HP. (open exhaust, etc.) GM said the used the name LT1 again in 92 because it eclipsed the orginal "high water mark" for a small block, the original LT-1. I think the new LT1's would be rated at around 380 GROSS HP.

LT-1 330 GROSS 255 NET
LT1 375+ Gross 300 NET

Even though the horsepower rating were lower (e.g., the 1971 LT1 was rated at 330 hp, but the 1972 LT1 was rated at 255 hp), the performance was the same. In 1971 and previous years, the horsepower rating was a gross figure calculated before adding any equipment (alternator, pumps, fans, etc.). But across the industry (not just GM), the ratings were calculated on a net figure. Many people incorrectly attributed the decrease to pollution equipment and the use of unleaded gasoline.

95wht6spd

I recently saw a 426 HEMI put down only 317 RWHP on TV. What were those supposed to be 500-550HP cars? I stock tuned 405HP Z06 will put down 360+ RWHP.