Home brewed cheap Dyno

[Don Perlick]

On Sat, 3 May 1997, Webb wrote:

> 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

	OK, I'm not the author of the software eing disucssed, but I 
think it is much simpler and less expensive to enter the gear, trans and 
tire info than to use another pickup on a line in the dash...  You make 
the run in one gear and know vehicle speed thru that calculation.

> 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. 
	I'm not quite sure, are you seeking to get part-throttle load?  
Of course, this would require something much more advanced.  This 
software is just to get a full-throttle power curve.  Such calculations as 
this uses DO assume a flat roadway--although you can do yourself quite a 
bit of good with relative numbers, at least.



> 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
> ;-)
	The software requires a drag coefficient and frontal area, I
think.  (don't have it)  I think the author intends to build a database 
for this info on his website.  The CarTest software on the 'net should 
also have a lot of this info.  Runs are advised to be made in 2nd gear, 
to minimize drag losses and safety concerns.  The details are at

http://www.charm.net/~mchaney/homedyno/dynokit.htm 



Regards,
Don Perlick
http://oeonline.com/~dperlick