Geekin' again

[Jon Davis]

George Roffe wrote:

> >"Hp at the wheels is the same as hp at the crank (minus drivetrain
losses).
> >We know the engine rpm and we know the hp at the crank"
> >
> >A critical part of what I wrote is ***minus drivetrain losses***.

> First, you just added that now.  Very important I think.

Everything within the quotes is directly from my earlier post, I added
nothing to it. Check the archives if my word isn't good enough for you.

> Second, I still say, "we do?"

> Please give me the calculation for hp at the crank minus drivetrain
losses.

hp @ wheels = hp @ crank - driveline losses

suppose for a moment:
gear ratio: 1:1
final drive: 4.25
engine rpm: 4250
engine torque: 100 ft-lb

engine hp is 100*4250/5252 = 80.9 hp
wheels will be spinning at 4250/4.25 = 1000 rpm
torque at the wheels will be 4.25*100 = 425 ft-lb (ignoring friction for a
moment)
hp at the wheels will be 425*1000/5252 = 80.9

Notice the transmission doesn't change the power output, only trades rpm for
torque.

Now if friction is included again, there may be something like 75 hp
measured at the wheels. Measured engine torque can now be calculated from
the measured power...

engine torque (minus driveline losses) is 75*5252/4250 = 92.7 ft-lb

jd