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Discussion Starter #1 (Edited)
I found a great web site to figure out gross hp form net rear wheel hp. Let see if you were making 265 gross hp in 1971 and converted it to net hp you would see around 175 rear wheel hp. If you want to figure out your car gross hp in 1971 you would multiply the net rear wheel hp by a factor of 1.5142857. Lets say your car puts out 100 rwhp in gross hp that would be 151.4 hp by the gross rating. Lets take it up a notch I made 328 rwhp and 364 rwtq If converted to gross it would be 496.7 hp and 545 ftlb of torque. That is much more than many of the big block motors that ford and gm put out. I had a 71 buick electra that put out 345 hp and 460 ftlb of torque. If converted into net rwhp it would be 227 hp and 300 ftlb of torque.
 

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I would change the 1.51 to something like a 1.25-1.35. Transmissions have advanced since the old days and a 51% decrease from engine to wheels is not likely.
 

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Pooperscooper said:
I would change the 1.51 to something like a 1.25-1.35. Transmissions have advanced since the old days and a 51% decrease from engine to wheels is not likely.
im assuming that the point of his post was to talk about how they were rated back then vs how they're rated now.
 

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Discussion Starter #5
the way the factory used to do it was with out a air cleaner, no accesory drive belts, water pump usualy with no exhaust manifolds or exhaust and the hp was measured at the crank. The way they do it now is with all acessories in place exhaust manifolds, full factory intake system and full exhaust system. Net wheel hp is measured from the rear wheels and most cars see a 15%-18% loss through the drivetrain.
 

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Basically, they went from "gross" horsepower at the flywheel to SAE rating at the flywheel. Yes, they now use a complete accessory system and emission controls during the test. Don't forget the correction factor has a lot to do with the overall rating.

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