svtguy said:
390hp translates into about 335rwhp, you could pull out a spark plug & most 03/04 Cobra would still put down that number stock.
that all depends how you work it out. Any form of calculation/working out is never going to be 100% accurate either, only a an educated guess as there are far too many variables.
The 15% rule:
390 /.85 = 331.5bhp but this would then be working on the bases of a SAE Net figure rated at the wheels, well as near as damn it as SAE Net has to be rated at the flywheel, but it would be using the same rating scale.
Rolling road dyno's (Mustang/dynojet) do not usually conform to this standard of rating so could easily dyno another 20+rwhp higher, but it would just be a different rating NOT a higher output from the engine. Same as $1 US dollar has a different value to $1 Australian dollar yet they are both dollars. So chances are if a car dyno'd around the 350rwhp mark by the time it has been corrected to SAE Net standards the figure would be around the 330-335rwhp mark.
However, some engine builders claim that most Mustangs usually loose 30-40hp thru the drivetrain regardless of engine output (except in some extreme examples) so 390bhp - 30 or 40hp would put them dynoing around 350-360rwhp mark on a rolling road dyno.
The % theory is very flawed, as different cars (makes, models even the same car with different wheels or milages on the clock (higher milage = more wear on bearings/bushing, etc.)) will all loose a different amount thru the drive train.
IMO the variable % rate is more accurate, basically it follows the logic of the higher the engine out the lower the % loss but hp loss still increases, for example (these are not real figures and are only used for illustration purposes):
250bhp flywheel, looses 15% (250 / .85 = 212.5rwhp)
A loss of 37.5HP
500bhp flywheel, looses only 10% thru drivetrain (500 / .90 = 450rwhp)
A loss of 50HP
The Cobra's are one hell of a car and rank high on my list in my fantasy garage, but if they ALL really produced over 400BHP SAE Net I'm sure Ford would have advertised the fact, for two reasons:
1. The Cobra is Fords premier performance model in the US (forget the GT, but that didn't exist then and is a totally different league), so there was no higher end car to steal sales away from in the Ford group, unlike GM they deliberatly underated the Fbody's so as not to over shadow the Corvette with the same engine, it was of course a lot cheaper to purly'Advertise' a lower BHP than actually go to the expense of detuning the units or building specific spec units just for the Fbody. Very clever in all reality.
2. The Corvette Z06 had 405BHP SAE Net, and although slightly more expensive could well be considered as an alternative to the Cobra, so it would have been beneficial for Ford to advertise the highest BHP but they didn't they advertised less than the Vette which again would indicate that the engine did only produce 390BHP SAE Net.
This all adds up that dyno numbers and even manufacutre claims can not and should not be taken literally as there will always be a variance in too many areas.
Another good example would be three 400bhp cars, one from the US one from the UK and one from Germany
The UK car is likely to be rated on the DIN system and 400BHP DIN is slightly more powerful than 400bhp SAE Net (if memory serves)
In Germany it would be 400PS (PS meaing Horse Power) but this is metric not imperial HP so 400PS would actually equal less than 400bhp SAE Net.
Gets very confusing doesn't it