freeyayo said:
but wasn't the Horsepower back then already calculated from the rear wheels and not from the engine ?
No. It was gross horsepower at the flywheel. Gross at the flywheel means that the engine was run on an engine dyno - not chassis dyno - with tubular headers, a bell-mouthed carb inlet with no air cleaner, no accessories, and the engine was run at its "blueprint" specifications. Production engines did not meet those same specs, and never achieved the 350 gross rating. (For example, the actual cylinder head cc volume of the GTO heads put the real compression ratio in production form at about 9.75:1. Advertised comp ratio was 10.75:1. The only way to get the comp ratio up to the advertised ratio was to run the minimum allowable chamber volume, which is what Royal Pontiac did with the Royal GTOs: They set the engine up to it's "blueprint" specs the way the factory did when they tested the engine at 350. Only this way could they get the engines to put out the factory rating). Other screwey things Pontiac did with the ratings is that the standard 400 was rated at 350 horse for both auto and manual cars. The manual cars had the "068" cam in them, but the auto cars had the little "067." Go figure how the two could possibly put out the same hp numbers when the difference between the two cams alone is about 10-20 horse...
The drop in horsepower from Gross to Net at the flywheel is about 20% (install cast iron manifolds, air cleaner, and all accessories). The driveline loss in the chassis (with mufflers and transmission) to the rear wheels drops horsepower about another 20%. If you figure that production engines put out an actual gross rating of about 300, you can get about 240 net at the flywheel. Then drop that another 20% for driveline loss and you get 192 at the rear wheels if everything is new, fresh, and the way the factory built it. If they got 175 on OverHaulin' , they're doing pretty good... sounds like the car runs about like a normal stock 400 GTO.
You can use some basic race math to figure this out and verify it. Most bone stock 400 "350 horse" GTOs run about a mid-15-second quarter mile if the car is tuned right (and you see a lot of them run quite a bit slower...). A 3700-pound car running a mid-15-second quarter is putting out 190 horsepower to the rear wheels. And that's exactly the same number as we arrived at in the discussion above....
A 3700-pound car putting out 350 to the rear wheels will run about a 12.8.