<VV> Actual vs. advertised hp

[BobHelt at aol.com]

Tony,
It seems quite apparent that you do not understand the differences between 
SAE Net, SAE Gross and advertised horsepower ratings back in the pre 1975 days. 
That seems to be the basic cause of your confusion. Although this is quite a 
lengthy discussion, I'll try to bring you up to date.

Back in those days, GM would run engine dyno tests (with their accurate 
dynos, by the way) with the engine configured exactly as it would be installed in 
the vehicle. That is, with stock air cleaners, stock mufflers, with cooling fan 
operating and accessories installed. The torque and hp numbers were then 
corrected to a temperature of 100 deg F. That temp was selected since it 
represented a typical under the hood real world temperature. The resulting numbers were 
the Net HP and TQ, and were know as the "as installed" hp and TQ. These are 
the real numbers! This is what the engines really developed.  This was the 
flywheel horsepower.

For the 80 hp, they were lucky to get 65 real hp (yes, 65hp! ). For the 110 
engine, 88 hp was it. For the 140 engine, 109-112 hp was all that was put out 
by those engines. If you don't believe these numbers then all I can say is that 
you have some serious problems.

GM then repeated all of these tests, but with no air cleaners, and and no 
mufflers, but with a lab exhaust system with some vacuum pulling the exh out. 
They also ran these tests by separately measuring the hp that the cooling fan 
took and ADDED this hp back in to the measured engine output! Thus the resultant 
output eliminated the power consumed by the fan. Then they corrected all the 
data to 60 deg F, which had the effect of raising the hp since engines work 
better with 60 deg air than with higher temps.  This data was called the SAE 
GROSS hp and TQ. We know that these numbers are much higher than the net figures. 
So for example the 140 hp engine developed 138 gross hp max!

But now the advertising dept got involved and bumped the gross hp numbers up 
to something they felt would make their cars comptitive and attractive. Thus 
the 140 engine now became 140 advertised hp.

So if you expect that a 140 hp engine is ever going to put out a real 140 hp 
in stock configuration you are fooling yourself. You should read about the RST 
Yenko Stinger engineering team that reported they had a heck of a time 
getting the 140 engine to put out an actual 140 hp even after all their mods.

You apparently are confusing advertised hp with something real. Never happen. 
Even the gross hp numbers are a lie since no one is ever going to test or run 
a car with no cooling fan to get real world numbers. You have got to use the 
net numbers. If you run any tests today, you need to make appropriate 
corrections.

If you want any corroborative engine dyno test data, please refer to Hot Rod 
mag, August 1975. 



I hope that this will bring you up to date.

Regards,
Bob Helt

In a message dated 3/9/05 12:57:27 PM US Mountain Standard Time, 
tonyu at roava.net writes:

> Real world horsepower tends to be not quite what the General 
> claimed.   I relate back to my earlier comment about how an independent 
> outfit blueprinted/rebuilt a 283 Chevy and dyno tested it on a MODERN 
> dyno.   That 195 hp (factory rating) 283 would not produce 195 hp no matter 
> what they did to it.   This was not a fly-by-night outfit, it was done by 
> the engineering staff of a major automotive performance magazine, done in 
> their contracted machine shop facilities.
> 
> Now:   How do we explain the discrepancy between measured power and GM's 
> claims?
>