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Re: Dyno accuracy for OBDII cars

To: autox@autox.team.net
Subject: Re: Dyno accuracy for OBDII cars
From: David K Yeung <dkyeung@juno.com>
Date: Thu, 25 Feb 1999 08:13:25 -0600
On Wed, 24 Feb 1999 23:14:45 -0800 Josh Sirota <jss@marimba.com> writes:
>Do any of you rocket scientists really understand how these modern 
>fancy
>emission systems work and can you tell me with a fair amount of
>certainty whether or not it's a waste of money to dyno one of these
>cars?
>
>Josh
>

it's not a waste of money if you want to know how much hp and torque your
car puts at the drive wheels....
this gives you a baseline such that later you can compare your car's
output to determine if any modifications have made a favorable change or
if a *seat of the pants* feeling that your car doesn't have the same
power it used to is really true.  The plot from the dyno can also be
helpful information for autox as it tells you where the peak torque and
hp values are over the entire engine rpm range, but you probably know
that already....Except for inaccuracies resulting from wheelspin, you can
derive hp figures based on acceleration data (but you won't get the
pretty plot).  For a manual transmission car all you need are the car's
laden weight and gear ratios, for automatics, it's a little more
complicated as you have to account for losses in the torque converter.

Dave Yeung
Johnson Space Center, Houston Texas



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