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Drivetrain HP loss answer Posted by Kevin K [Email] (#374) [Profile/Gallery] (more from Kevin K) on Thu, 15 Apr 2004 23:37:35 In Reply to: Drivetrain HP loss question, DaveD, Thu, 15 Apr 2004 20:03:56 Members do not see ads below this line. - Help Keep This Site Online - Signup |
your intuition is correct, it's not a constant percent.
the general loss values used .. 11% transverse fwd, 15% rwd, 18% C900, 20+% awd, are based on STOCK engines and hp ratings, vs typical stock dynojet(48") runs.
reality is there are power independent losses, like just flexing tires on rollers, or churning oil. load dependent losses include gear mesh friction, heat due to shear flex of tires, etc.
my logical approach is to assume 1/2 of loss is constant, other 1/2 is load dependent. C900 example:
160 hp stock, 18% loss is 28.8 hp, so 131.2 hp on honest dyno at sealevel and 66F.
So dyno stock at 131.2:
stock eng hp = 131.2 x (1/(1-.18)) = 131.2 x 1.2195 = 160.00
... or by 50-50 method:
eng hp = (131.2 +14.4)/(1-.09)) = 160.00
Dyno at 220 hp with mods, same temp and sea level.
eng hp = (220 x 14.4)/(1-.09) = 257.6 hp. The strait 18% method would predict 268 hp, a bit more.
the higher the increases hp, the more the correction approachs the 1/2 of stock % loss value of 9% for the C900.
some dynos with small roller pairs, like mustang, and maha, run higher % losses due to more severe tire flexing.
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