<all> home dyno kit??

Roger Heflin rah at horizon.hit.net
Sat Jan 30 02:27:18 GMT 1999



On Fri, 29 Jan 1999, Jay Wallace wrote:

> At 07:06 PM 1/28/99 -0500, you wrote:
> >>
> >>> At 08:24 AM 1/28/99 -0500, Dan Llewellyn2 wrote:
> >>
> >>> >level ground.  At least were I live, level stretches of road where
> >>> >you can get up to speed are rare.  If they incorporated the data
> >>> >from a G-field measuring device, like an Analog Digital ADXL05,
> >>> >you could calculate horsepower even if the road was not level.
> >>
> 
> 
> About 6 - 8 years ago (?) in Road & Track there was a Tech Tidbit
> (or some such) article about accelerometers / stopwatch / coastdown
> to determine rolling and wind resistance and horsepower. Does
> anybody have the reference?
> 
No, but it is pretty easy to do.

Get the car to 65, and time how long it takes to get down to 55 in
neutral.  Given the car weight, you know how much energy was in the
car a 65, and you know how much energy is in the car at 55.  Subtract
those, and divide by the number of seconds.  here is the equations:

	energy = 1/2 * (( mph / 3600) *1609 ) ^ 2 * ( mass / 2.2 )
		 
So with a 3000 lb vehicle that takes 10 seconds in neutral we have:

	energy at 65 = 575 * ( 10 ^ 3)
	energy at 55 = 412 * ( 10 ^ 3)
	
	change in energy is: 163 (KW)

	change in energy per second: 16.3 KW
	
	1hp = 746 watts, so hp is 16.3 / 746 = 21.84 hp.

So,

	21.84 hp is required to overcome wind/friction at about 60mph.

			Roger

	




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