"The fastest magazine test results from this period were obtained by MOTOR TREND Magazine, which managed to extract a 13.38 ET @ 105.5 MPH from their 3,810 pound GS Stage 1 coupe test car. Using Hale's Trap Speed formula, this result indicated actual "as installed" peak HP of approximately 360 SAE Net (ironically the same as its advertised Gross Figure" - Wikipedia on "Grand Sport 455"

Now I realize this is a Buick and not an Olds, but its an interesting concept. I mentioned this just a little while back and got a rather rude response for even suggesting such an outlandish idea. But it seems Motor Trend saw some truth in this too. It seems to me (and testers apparently) that the best estimate of your car's factory horsepower rating, as backward as it sounds, is to actually go by the Gross rating rather than the Net rating.

The theory behind that is this, Gross ratings are not real-world estimates of horsepower ratings, in actuality you have many accessories and more than just a flywheel or flexplate between your power and your wheels. However, the amount of power you would lose between switching from the Gross rating to the more realistic Net rating (with accessories and transmission attatched, as it would be in the real world) is compensated by GM's (and in actuality all American muscle car manufacturers of the time) notorious trend of under-rating their performance cars' outputs.


Here's a dulled down representation of what this all means:

Gross horsepower = 360
Compencate for Net rating practices...
Net horsepower = 300
Compencate for GM's under-rating practices...
Realistic horsepower estimate = 360



Its an interesting concept at least...thoughts?

 

There are formulas for estimating HP from quarter mile times and trap speeds, but this is only an estimate. Obviously you need to account for trans, gearing, traction, etc. Also, acceleration is not constant over a quarter mile, so again this is just an estimate. As for the under-reporting, Roger Huntington once wrote an article about this back in the day and calculated that the 1970 W-30 actually put out about 440 HP. The 370 factory rating was driven more by the corporate edict of 10 lb/HP, not reality. Think about it, a 3700 lb curb weight magically gets a 370 HP rating...

 

I prefer the gross hp rating as a baseline. Anything added to the engine from there is a subtraction. The net rear wheel hp will vary based on weight, trans, gearing, and accessories installed.

 

True, and this is only suggested as an estimation of factory specs. Lots of things on a car change over time and even two of the exact same car fresh out of the factory will put out slightly different power. Not something to take as gospel but a fun estimate