gross verses net HP
 

what is the differents between gross and net when talking about hp. like in old mustangs they use gross. but now days they use net what is the differents between them. and how would I convert it if possible.


sorry if I am not making any sence

thanks
ford kid

Net/gross HP
 

Before about 1971, manufacturers used gross HP figures to rate the engines. They wanted the highest numbers they could get for advertising purposes. To do this they put a "seasoned" (well broken in) engine on an engine dyno. Dyno headers didn't even have to fit in a car. Large srtaight exhaust with no mufflers and no bends was used. No parasitic accessories were attatched. No fan, alternator (genrerator) and sometimes not even a water pump. Certainlly no AC or PS. The only drag on the engine was the oil pump and the fuel pump. The engines were often "super tuned" by some racing guru like Smokey Yunick if they really wanted the highest numbers.

The Feds and the insurance industry started giving the manufacturers grief about "over powered" muscle cars and heavy pollution, etc. So in 1971-72 the manufacturers capitulated by using net HP figures that are lower. This net figure represents flywheel HP that the engine would produce as installed in a new vehicle. All engine accessories except AC and PS are attatched. Full factory exhaust including cats (if applicable), stock mufflers, and pipes with all the bends are installed. The engine is just like it came off the assembly line with no special tune up.

The net figures are usually about 80-85% of the gross figures.

Rev

ehy thanks Rev.

so in other words my 66 coupe I6 cyl is really only putting out about 100 instead of 120 like the book says. right.

thanks again cuz I was really confused on that.


thanks
ford kid

That's right fordkid68. And you would lose another 17-25% (depending on the drive train), if you measured it at the rear wheels. That's how most of us have to do it (on a chassis dyno).

Rev

thanks. damn you loose alot of hp from flywheel to wheels.

thanks again
ford kid