dyno stuff

[Programmer]

Clear--perfectly. There's no data to "input" into the MAHA software.
Therefore it is
measuring raw data at the rear wheels. Just having a little trouble how the
HP numbers
are calculated...

Lyndon.
----- Original Message -----
From: Eric Bryant <BRYANTE at ghsp.com>
To: <gmecm at diy-efi.org>
Sent: Wednesday, May 02, 2001 9:11 AM
Subject: RE: dyno stuff


> > Let's say the engine outputs 200 ftlbs torque at the
> > crankshaft at a given
> > RPM. Why would you see a similar number at the wheels when the
> > "differential" multiplies the torque ? You shouldn't right ?? I've had
> > numbers as high as 1774 ft/lbs on a low 11 sec car, but HP
> > numbers around
> > 420. How did they do their calcs ? At this point, I'm the
> > only one in Canada
> > with this dyno...and nobody can give me answers.
>
> Well, if you have a motor putting out X ft-lbs of torque at Y RPM, and a
> final drive ratio of Z, then you'd measure XZ torque at the rear wheel at
> Y/Z RPM.  So, assume the engine makes 200 ft-lbs at 5000 RPM, and you're
> testing it in a gear that results in a 10:1 final drive ratio.  I'd expect
> to see something less than 2000 ft-lbs of torque (to account for
drivetrain
> losses) at 500 RPMs at the rear wheel.  This is probably what your dyno is
> doing - it's taking a "raw" number and not accounting for gear reduction.
> HP ends up being a calculation (power * torque * some constant), so the HP
> number will be the same whether the dyno spits out "raw" or "corrected"
> torque.
>
> A Dynojet dyno uses the roller speed and the engine speed (through an
> inductive spark wire lead), and then comes up with "rear wheel torque" -
> which is actually "crankshaft torque as measured at the rear wheel".
>
> Is that clear enough, or did I just muddy up the waters?
>
> Hope this helps,
>
> Eric Bryant
> mailto:bryante at ghsp.com
> http://www.novagate.com/~bryante
> --------------------------------------------------------------------------
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