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.
> 
> The home dyno records the pulse from the inductive pickup on a small plain
> voice recorder and then feeds this to a sound blaster card to produce a
> WAVE file then reads this file.
> 
> A stereo recorder could be used to record the inductive pickup and the
> speed sensor one on the right channel and the other on the left to get two
> distinctive pulse patterns and produce a WAVE file then read it and
> calculate what we need to get car speed engine speed and the rest for HP
> and torque.
> 
> Very cheep way to get a reliable chassi dyno.
> Most of us have a inductive timing light, computer with sound blaster.
> Only thing missing is a stereo tape recorder (a stereo camcorder would be
> perfect)
> And a few feet of cables and a few plugs and the big one the software to
> convert the pulses in the WAVE file to readable format for you favorite
> database program.
> 
> Any one interested in writing a simple bit of software to convert this?
> 
> // marchildon at usa.net                                            //
> // Alain Marchildon                                              //

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!