Date:         Fri, 1 Jun 2001 21:53:23 -0800
Reply-To:     Mark Keller <kelphoto@ISLANDNET.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mark Keller <kelphoto@ISLANDNET.COM>
Subject:      How dynamometer measures horspower and torque. A Must have url
Comments: To: Robert Keezer <WarmerWagen@AOL.COM>
Content-Type: text/plain; charset=us-ascii

Robert,

The dyno article I read, http://yarchive.net/car/ and others, state that
dynamometers read the engine's torque and the horsepower is
mathematically derived by: Torque x RPM/5252= horsepower.

Knowing the formula has made life easy to wade through antedotal
"improvements" of driving a van into the garage with  a sick engine and
out with a converted engine. While there is still wiggle room in the
argument that engine X can reach it's torque faster than engine Y, I'm
satisfied to know how much torque and horsepower  each of these
transplants have at at least one RPM.

As to the Crank horsepower vs Wheel horsepower.  A GENERALLY accepted
loss of power available to turn the wheel is 30%; it's just another
mathematical derivation.  Since it's applied to all corrected crankshaft
torque values it just gives general picture of how much power is
available when driving.

Road horsepower is the amount needed to propel the vehicle on flat
ground; it varies with weight, ride height, and added aerodynamic drag.
The Carat I have cruses at 13" vacuum, about 80% of available power at
65 mph, and 3800 RPM.  So the road horsepower is around. 80% of 58 hp or
46 hp just to drive my automatic on level terrain.  This would yield a
approximate reserve of 12 hp for everything else: hills, wind, more
weight, and etc., without downshifting.

Like you mention, running in a lower gear, can produce dramatic effects,
but I'm not willing to push to much past the 4400 RPM, max. horsepower.
At 25 mph, and 1st gear at 4400, the Vanagon can pull like a train! It's
all in how you whip the horse!

Sincerely,

Mark Keller
91 Carat
Cowichan Bay, BC