Home brewed cheap Dyno

[Webb]

> Alain Marchildon wrote:
> >
> > After reviewing the home dyno software package available on the F-body list
> > it got me thinking that if you want an accurate home built dyno with the
> > least amount of money invested the best way to go would be similar to what
> > is already done but instead of calculating the vehicle speed with the trany
> > diff and tire ratios why not use the speed sensor that is buried the dash
> > of most modern cars, they give something like 2000 pulses at 60mi/h and
> > then get an inductive pickup to read the engine speed like the Dynojet
> > chassi dyno do except instead of reading the car speed they read the drum
> > speed.
> > The rest is pure math.
> >

<snip>

 Seems to me that either you are missing some data here, or I am missing
 your point.
 
 You have managed to acquire the vehicle speed, and the engine rpm. You
 have no data on the engine load.
 
 To give an example - the objective is to calculate the power output of
 the engine, but it would be vastly different if we had 3000 RPM and 30
 MPH on the flat, versus the same numbers up a steep grade.
 
 Some continuously variable transmissions might allow the calculation
you
 want, if you had the proper torque/ratio curves, but I think that would
 be more complex than you had in mind...
 
 No way to assume it's flat, without detailed knowledge of the vehicle
 drag coeff. Of course you might get that by throwing the vehicle in
 neutral and recording how quickly you decelerate.
 
 Our main interest is in Max HP - I'm having visions of a bizzare series
 of high speed accidents, that could wipe out the membership of this
list
 ;-)
 
 I have a need for a homebuilt dyno - so straighten me out if it's me
 that needs it!