Steve, Listers,
I think we've probably all read or heard that 1/4-mile trap speeds are a
pretty good indication of your car's horsepower output. It's better than
ET's because it's not so sensitive to hook-up and reaction time. But, I've
never heard anyone suggest that 1/4-mile numbers reflect engine torque.
There is a good reason for that. I challenge anyone to try and calculate
their 1/4 -mile times just from engine torque. The following two links give
empirically adjusted equations for calculating 1/4-mile and other related
performance numbers from horsepower.
http://www.web-cars.com/math/calculations.html
http://www.karlsnet.com/mopar/formulas.shtml
If you do a Web search on, for example, key words 'horsepower',
'acceleration', 'formula', etc. you come up with a lot of hits. Some of it's
good and some not so good. I won't bother commenting on some of the, shall
we say, conceptually challenged opinions out there, but there is a more
subtle and rather pervasive viewpoint that even some of those that at least
get the math right are a bit confused about. The statement is often made in
one way or another that it's really 'torque' that makes acceleration and
horsepower is, I guess, somehow a bit too ephemeral. For example, this
statement: "Many engine builders will say that torque is what wins races and
too much emphasis is put on horsepower. It is true that torque is what
actually pushes the car, but torque and horsepower are directly related, you
can't have one without the other."
[http://www.grapeaperacing.com/GrapeApeRacing/tech/miscpower.cfm] As I
previously stated, at the most basic level it's really force that
accelerates the car. Force is a primary unit. Torque, on the other hand, is
a mental construct - a concept - force times distance - and a useful one
when properly applied. The same is true of power, it's a concept too. So
it's no more correct to say that it's torque that 'really' accelerates than
to say it's horsepower. They are both concepts that are related to
acceleration. However, as the equations given in the above links
demonstrate, it's much easier to calculate useful performance results
knowing horsepower than knowing torque. Now, on the other hand, if you want
to know whether your axle is going to break, torque is what you need to
know.
Bob Palmer
rpalmer@ucsd.edu
rpalmerbob@adelphia.net
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