Net HP VS Gross HP?

Is there that much of a difference? I was looking around and it says net horsepower is generally 20% of gross, that would mean that my brothers '66 Catalina has 260HP instead of 325 and my '60 LeSabre would have 206 HP. Is that right? o No:

 

As a ballpark figure, that seems about right, but by no means 100% accurate.

 

That's a little depressing uzzled:

 

Well.........mine's stock, except for a mild cam and springs, and just after I broke her in, they had a "dyno day" at the local speed shop......$25, I could afford that. Anyhow, mine is rated 360HP at the flywheel, and my best of 3 runs was 220 HP :ball: .........keep in mind that I later discovered my cheep new napa fan clutch was locked solid and she was running so rich we all were choking. Then when it started pinging they shut her down. Maybe now that I have things tweaked I'll go back for a second test. :Brow:

I don't know what the torque was, they told me on an auto trans you can't get an accurate reading. :bglasses:

 

Here we go again.................

 

Yeah, i know all that. I was asking if the 20% figure was correct

 

I'd say so...my 350 is built as a 315hp '70 GS engine, plus HEI, a really good carb, and bigger exhaust pipes. I put it on a track 3 weeks ago, and doing the math, it works out to around 260hp at the wheels, right at a 20% "loss".

 

Do the math:

Check HP ratings at the same RPM for the same engines with the same CR in 1971 (gross) and 1972 (SAE).
Check 10 engines and get an average......

 

Rear wheel HP is not the same as SAE HP.

 

You know, I'll bet that explains the differences I saw between some online calculators... :error:

That, and I need to go put my car on some scales and actually find out for sure what it weighs, and not rely on posted curb weights. ou:

 

I know somewhere I've seen HP ratings for 1971 that gave both net and gross figures. I recall reading that GM published both that year so as to not confuse people as much. Can't seem to remember where I've seen it though.

BTW, you stated net was gross 20% of gross.....I believe 80% of gross is a little more like it, for a 20% loss. :TU:

 

uzzled:

 

From this website;

So my previous math wasn't that far off, I was just calculating SAE net (flywheel) hp, instead of horsepower at the ground. Which works out to 205, btw... Hmm...so if I wanted to get my (estimated) 4500lb LeSabre into the 13's and over 100mph, I'd need 350 hp at the ground, 438 SAE net, and 547 SAE gross horsepower!!! (+20% at each measurement.)
:jd:

 

yeah, that's what I meant ou: