I'll try this again with an updated address.
Bud
----- Original Message -----
From: Bud Bohrer
To: Tigers Digest
Sent: Sunday, February 13, 2005 10:17 PM
Subject: Torque, Horsepower and Acceleration
I think Veeseeoso has it about right, see below, but I'll throw another log on
the fire. Per the AUTO MATH HANDBOOK, p.77 quarter mile elapsed times are
determined by the cube root of the (weight/horsepower), specifically,
multiplied by 5.825. The constant was derived from data from various quarter
mile times, is updated from time to time, and is ascribed to Patrick Hale,
Racing Systems Analysis. Or, you can consult
http://www.quarterjr.com/index.htm and hit the tab for the QuarterJr
software.
The underlying theory is that it takes power (Horsepower) to increase the
kinetic energy (1/2 x mass x velocity squared), thus velocity, of the car. If
you want time over a shorter distance, or time between two speeds, the
constant changes but not the form of the equation. A good approximation to
the constant can be derived by assuming constant horsepower applied over the
quarter mile. Yes, there are some gross assumptions in that approximation,
such as the tires don't spin at launch and the engine is always at constant,
peak power, but it works out reasonably well. So, we're back to Veeseeoso's
principle, basically, shift beyond the Horsepower peak as seen at the rear
wheels to try to keep the power as close to peak as possible. Yes, it's
convenient in an autocross to use one gear; you're VERY busy with turning,
braking and accelerating. But, if you do shift and have the traction and
ability to use the power (and therein lies the challenge), you'll be quicker.
Some cars, Honda S2000 and Acura Integra, have the power but little torque and
must shift to be competitive, and they are very quick at autocrosses.
Bud
Date: Sun, 13 Feb 2005 18:43:23 EST
From: Veeseeoso@aol.com
Subject: Re: 15 inch tires
Listers,
With respect to performance motoring:
It is better to make torque at high rpm than at low rpm because you can take
advantage of gearing in performance situations such as spirited driving,
autocrossing and road racing.
In these instances the ideal shift point should be a small percentage past
the horsepower peak (5-10% in most cases). If you were to graph this you will
see that this will allow a greater area "under the curve" to pull through the
next gear.
Design for a high flat torque curve, shift past your horsepower peak, and
take advantage of your gearing!
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