Quote:
Originally Posted by doc7000
I do not totally buy into the under rating idea, it is really tempting especially since cars in the 1960s were at times notoriously under rated.
The SAE testing method involves testing with a third party witness of the test, so I do think that it isn't likely to be under rated.
As far as drive line losses go there are some vehicles with really low drive line losses, so it is possible that the Camaro SS is only seeing 10-15% drive line loss (maybe closer to 12 or 13%).
However dynos are only good for one thing really, one is to test the modifications that you make (this is why tuners make a baseline run). The reason being is that depending on the dyno used and the conditions that the car is run in numbers will vary widely. This is why you are suppose to use correction factors, you really can't compare cars tested on different dynos let alone results that have not been corrected. So assuming that the 2016 Camaro SS has a 13% drive line loss, it is possible that on that day their Camaro really was producing 475BHP (some 20 over the SAE rated numbers). However once the numbers are corrected then they would come down to 455BHP ...
Also food for thought, I believe it was motor trend who tested a GT350 and GT350R Mustang and they got a result that was about 3BHP higher for the GT350R. Production variations withstanding the GT350R has carbon fiber wheels which weigh less then the wheels on the standard GT350 which can account for the difference. Meaning that the GT350R has less drive line loss then the standard car.
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60's cars were underrated but used a rating system that showed much much higher numbers than today's, so they were actually mostly "over rated". The way they rated hp changed sometime around 1973 and then again about 8 or 10 years ago. The numbers got lower and lower again, when the same engine was used.
GM uses SAE. Had they used STD or STP, that 455 or 458 would have been more like 470.