Automotive HorsePower; brake, wheel, or real?
Automotive HorsePower; brake, wheel, or real?
(OP)
I follow a sports car forum. A recent post was someone’s posting of an incoherent article about how to calculate HP using times to speeds during acceleration.
I took interest and tried to write a simplified version using minimal mathematics. Basically calculated power as change in KE over time.
From another poster that had provided a plot taken from those new fangled GPS data loggers. His intent was to show how his +500 bHP engine (documented) now achieved a 0 to 60 mph less than 4 seconds. Appling the KE to power calculations the required HP to do so is about 250 wHP. there is an "Eng Tool Box" calculator that gave similiar results
So my query is why does if appear to take 2X the required at the engine? Is driveline losses that much?
I took interest and tried to write a simplified version using minimal mathematics. Basically calculated power as change in KE over time.
From another poster that had provided a plot taken from those new fangled GPS data loggers. His intent was to show how his +500 bHP engine (documented) now achieved a 0 to 60 mph less than 4 seconds. Appling the KE to power calculations the required HP to do so is about 250 wHP. there is an "Eng Tool Box" calculator that gave similiar results
So my query is why does if appear to take 2X the required at the engine? Is driveline losses that much?





RE: Automotive HorsePower; brake, wheel, or real?
Mike Halloran
Pembroke Pines, FL, USA
RE: Automotive HorsePower; brake, wheel, or real?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Automotive HorsePower; brake, wheel, or real?
that makes sense.
since I sleep on it I had a though, would the descrepancy be also the fact documented engine power is at a peak, where measure performance is over a wider rpm range, thus performance is effective power "under the curve"?
so I think I now see where
the difference in brake to wheel would be the 15% driveline effeciny,
and
the difference from wheel to "real" is the power required due to driveline inertia
Thanks
RE: Automotive HorsePower; brake, wheel, or real?
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Automotive HorsePower; brake, wheel, or real?
a very quick google search on the subject implies, like Greg mention, the "rule of thumb" equivelant mass of the vehicle is 1.4 its actual. there is a LOT more engineering I should study, if I wish to continue understanding this
I think I got my answer! thanks
edit...FYI
I found this article
http://hpwizard.com/rotational-inertia.html#simple