View the file I have attached If you can tell me how they dyno the engine at the flywheel (the plate directly behind the engine directly connected to the crank) with the engine installed in the vehicle, then I will believe you. I have done way too much research on this subject in my ase certification classes to just believe you off the bat.
Yet again I found another example. The last image was from a ford shop manual. Here is one from a GM manual for a chevy II/Nova. This one is more clear about the subject.
SAE Net Horsepower became the standard measurement in 1972, and is still used today. SAE Net horsepower is the horsepower generated by the engine at the flywheel with all accessories attached. This change was made to reflect the numerous energy sapping accessories that cars began to have, such as an A/C Compressor and alternator, and thus was a better representation of the actual power generated by the engine. This number is always lower than the SAE Gross horsepower. Therefore, the same engine could have been rated in 1971 as 360 SAE Gross Horsepower and in 1972 as 300 SAE Net horsepower without any reduction in "power." Taken from: http://www.musclecarclub.com/library/dictionary/engine-terms.shtml Not trying to start a battle of who's better David, it is just that this very reason was the primary reason why I went with a roller motor, because I am on an extreme budget, and was a real easy way to pick up near 100 extra horses without building the original block.
Ken Merring.... ....uh, could you get out your calculator and protractor and clear up this confusion. For the record, I have always understood the 'net' horsepower to be at the back of the transmission with all smog accessories installed on the engine but for example, the A/C not running. The smog equipment would have been installed as required and mufflers, air filter assembly etc. would have been installed as well. I do not know how if they determined HP using A/T or manual transmissions. Prior to '72 I understood the HP to be measured at the flywheel without restrictions such as mufflers and smog equipment. Ken knows the answer to this question. And you just wait. He is probably going to give you a 3 part answer defining Gross HP, Net HP and HP at the wheel. Ken? Seth
I've never understood the reading to be at the rear wheels. They just didn't do that in the seventies. I have always understood that "net" was with all accessories attached, but still at the flywheel. While the above descriptions help, they can be misleadeing. When they say "intalled in the vehicle", I believe they mean "AS installed in vehicle". If they really did rear wheel horsepower numbers, why no difference for automatic transmissions vs. manuals? It is well documented that automatics suck up about 25% of engine horsepower, where manuals are in the 15% range. On a final note, and although I took the tests some time ago, I am an ASE certified Master Technician, and I do not remember having to know net vs. gross horsepower numbers at the time. I also know some tech writers as I am now in transportation publishing, and I know that they don't always get it right. A computer controlled, fuel injected, roller cammed motor damn well better make 100 hp more than a smogged out, cam-retarded, flat tappet, carbureted one. But only the dyno will tell.
Got here late. The factory engine model is usually dynoed to the flywheel with all normal engine accessories in place. The transmission losses for each offering is already known so they don't run a trans into a dyno cell. The 80/90s 5L HO engine is rated at 225 at the flywheel and usually see 200 to 210 at the rear wheels on a chasis dyno. The major differences between the old 302 and the 5L are quite a bit. Compression is up to 9, roller cams allows more area under the valve lift curves, heads are improved, computer control adds to the responsiveness, poor excuses for factory performance headers etc. Still this engine doesnot flow very much more air than the old 302, just much more efficient. The airflow is still determined by the same block displacment, just better use of it and a little more volumetric efficency.
