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Path: utzoo!linus!security!genrad!decvax!tektronix!tekcae!philw
From: philw@tekcae.UUCP (Philip White)
Newsgroups: net.auto
Subject: Re: 1hp/ci
Message-ID: <23@tekcae.UUCP>
Date: Fri, 25-Nov-83 21:19:52 EST
Article-I.D.: tekcae.23
Posted: Fri Nov 25 21:19:52 1983
Date-Received: Sun, 27-Nov-83 03:23:43 EST
Organization: Tektronix, Beaverton OR
Lines: 28

The question "why can't they make car engines anymore
with over one horsepower per cubic inch?" was discussed
at length a couple of months ago in this net.
Someone pointed out that motorcycle engines routinely 
produce over 1 horsepower per cubic inch these days, 
even if cars don't.
   I think I can explain why this is - the smaller 
motorcycle engines rev higher.
HORSEPOWER = K * TORQUE * RPM   where K is a constant.
If engines are compared on the basis of peak torque per
displacement volume, motorcycle and car engines of all
types are extremely close.
  I looked at seven motorcycles from Cycle magazine, versus
seven cars from Road & Track.  They were selected by 
being the first seven I ran across.  The bikes ranged from 
.055 to .062 ft-lbs/cc (love those units), while cars
were between .051 and .060 ft-lbs/cc.  The bike mean was
5% above the car mean, which is not much difference.
   The bike engines were all smaller and therefore could 
rev higher, with torque peaking at higher rpm than for the cars.
Therefore the average bike has more power at peak torque
than a car at its peak torque, per unit displacement volume.
It should then be no surprise that power at the power peak
rpm will also be higher for bikes than for cars.

       Phil White   Tektronix, Beaverton, OR
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