Quote:
Originally Posted by superdutybob
The difference between net and gross is pretty simple. Both are measured at the crankshaft. Gross is the engine only with no accessories hooked up and running free air intake and exhaust. Net ratings are done with the correct vehicle exhaust system, all accessories, and the correct vehicle airbox or filter system in place. It takes power to turn the accessories, therefore a lower number.
If you'll notice, the 73-74 SD-455 HP was rated at 4000rpm. The engine continues to make power well past that rpm. Probably made 350ish at 5200 would be more correct.
There is a new SAE rating system that the manufacturers started using 5-6 years ago where you actually do a net rating with a witness from SAE that certifies all of the parts of the engine. It levels the playing field between all of the manufacturers. You MUST rate your engine HP +/- 1% of what it makes on rating day.
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VERY well stated, Mr. Woodard.
Your point about the "rated" HP RPM for the SD engine is a point I most certainly meant to make, and completely forgot. Thanks for chiming in!