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Re: some calculations
Sounds a like a pretty good aproximation for samller lighter sports cars
in very thin speed range.
The discrepancy with sedans arizes because the formula does not take into
account changing aerodynamics of the car (variation of Cd etc..).
Thanks for the info.
On Wed, 14 Aug 1996, Withu Ruksvanichpongs wrote:
> I haven't try it yet ,because I don't know the frontal area of my
> In the article ,they try to tell us how much more power we
> need just to increase top speed a few mph.
> their example is Porsche 944
> Cd 0.33
> frontal area of 20.45 sq ft.
> assume the target speed is 200 mph
> Power needed is 8.7E-06*0.33*20.45*200^ = 469.8 HP.
> Oh,I just see the other one.
> new power/old power = (new speed/old speed)^3
> Their Porsche now has 331 rear wheel h.p. and does 175 mph . they
> input these info. in the second formular and use 200 mph as new speed
> ,the new power is 493 which is very similar to 469.8 from the first
> I don't think it is very accurate ,because many tuned German sedan
> also does 175 mph with about 300 *flywheel h.p.* (all of their h.p. means
> rear wheel h.p.,which is much lower than flywheel h.p.)
> Now I'll try the second formular for my car,but I'll use flywheel
> h.p. anyway. old speed=150 old power =230
> new speed=? new power = 280
> the answer is 160 mph..
> they convert Porsche's331 pony in to
> flywheel h.p. of 400.!) 469.8 h.p. they need is still a rear wheel h.p.
> I hope this is detailed enough