Quote:
Originally Posted by Hib Halverson
Well, uh...(choke)... 
I don't know how this thread ended up being a wee-wee length contest. I thought we were talking about how GM has rated engines, the differences between the old "gross" power rating system and the current "SAE net" power rating system and the ins-and-outs of comparing power output using dynos. |
Ins-and-outs of comparing power output via dynos...WAS exactly my point!
Engine output and how it is measured has been a delema for real engineers for some time, hence references to the evolvement of various SAE standards for measurement, and their revisions over time. And, I was agreeing (somewhat, perhaps) with you with regard to the ambeguity ("grain of salt", you said) that results between direct vs. indirect measurements.
You misunderstood my piont; no dick-measuring at all. Take "yours and mine" out of the discussion and say A = 504 net chp via 18% correction between the tire and the flywheel, and B = 508 net chp via 15%. That amounts to a 1% difference in net chp - well within the margin of error to the point of being essentially the same.
However, measured at the tire, B = 4% more than A. We can agrue the differnces between dynos too, but
all things being equal, which horse are you going to bet on in a race? Again...reinforcing your agruement regarding (essentially) the pitfalls of extrapolating measurements via indirect methods, and my point that measurements at the tire are much more indicative of motor output, but terminal velocity resulting from WOT accelleration testing is probably superior to anything else we have to determine real performance, i.e.,
where rubber meets the road...maybe.
Interesting discovery... In boning up on SAE standards re this topic, I ran across "taxible horsepower". Essentially a British standard where a horsepower tax was levied on manufactures where the number of cylinders and bore diameter were the key ingredients in the calculation. As result, Jaguar (and others) motors in the 50s were built with fewer cylinders and strokes significantly longer than bore diameter. Eventially, the standard was relaxed in order to compete effectively with other world manufactures that were trending toward over-square bore/stroke via bore diameter. Another example of govenment and unintended consequences. Makes ya wonder what sports cars would be like w/o any restrictions, huh? Supercharged V12s or V16s maybe?
Anyway...I agree w/ others that this topic has probably been beat to death...long ago.
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