I was always under the impression that the 'old way'(Gross HP) would yield higher numbers than the 'new way'(Net HP). The way it was explained to me was they used to measure an engines power output WITHOUT all of the accessories hooked up. Today, and engine's power is measured WITH the alt., smog pump, pwr. steering pump, full exhaust system, etc. hooked up to the car.
Think about it. Many of the old muscle cars with 400+ cubic inch Big Blocks, and BIG hp numbers really only turned about the same trap speeds as say, an LT1 300hp Vette. Around 100mph give or take.
I just watched an American Muscle Car show on Speed Channel about the 426 Hemi Superbee's. They said that car was designed to go 100 mph +/-stock in the 1/4 mile. I'm not sure how accurate that is for completely stock, but weren't they rated around 425hp, at least? Now,take something like a ZO6 Vette with its 405 hp --->116mph in the 1/4! There can't be that much difference in weight to make that big of a difference in trap speeds.
ET's are a wash as there are way too many variables.
early 70s dynoed six pack 69-superbee,mild tune with fenderwell headers,at the rear wheels,276hp,car would run 12.50s with slicks and headers open, gearheadbill
As for this. IF it would hold together, a 405hp ZO6 with slicks, running 116mph through the traps, would be a mid-11 second car. SRT-10 Vipers with slicks would be in the TENS!! Until they both broke their halfshafts...
Of course, all of this is just my opinion. I could be wrong.