dyno stuff

[Programmer]

Here's one--I had a SB Dodge car at 6200 RPM, peak torque was 1774 with a
manual trans. I had the
torque calculated at 389 ft/lbs at the flywheel--then doing the math it was
459 HP--yet the actual dyno HP was substantially less. That's why I'm still
questioning this thing...SnapOn's formula is really strange--as soon as I
can find it again, I'll post it.

Lyndon

----- Original Message -----
From: Marteney, Steven J. <smarteney at xlvision.com>
To: <gmecm at diy-efi.org>
Sent: Wednesday, May 02, 2001 12:46 PM
Subject: RE: dyno stuff


> 1774 ft/lbs div by 3.73 gear (and 1:1 3rd gear) = 475 ft/lbs at flywheel,
> ignoring loss.  Let's say that's the torque peak at 3500rpm.  Then HP =
> Torque x rpm / 5252 which equals 316HP at that point.  So, as the torque
> falls away but the rpms pick up, you may see 400HP with this combo.  (I
took
> a lot of liberties in my assumptions.)
>
> Their HP numbers should be correct since HP is basically torque for a
period
> of time.  For HP, the gear ratios are not needed.  The power is a
constant,
> ignoring loss.  The engine is producing some fixed torque in a time
> interval.  The gears produce more torque, BUT over a longer period of time
> (i.e. at the expense of rpm) so it all cancels out.
>
> Does this help?
> Steve
>
> -----Original Message-----
> From: Programmer [mailto:nwester at eidnet.org]
> Sent: Wednesday, May 02, 2001 1:36 PM
> To: gmecm at diy-efi.org
> Subject: Re: dyno stuff
>
>
> 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
>
> --------------------------------------------------------------------------
> --
> > To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
> > in the body of a message (not the subject) to
majordomo at lists.diy-efi.org
> >
>
> --------------------------------------------------------------------------
--
> To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org
> --------------------------------------------------------------------------
--
> To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org
>

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org