Re: A quick, easy definition of torque?

[16v Jason <jason@scirocco.org>]

At 10:33 AM 5/12/2000 , DNK006@aol.com wrote:
>BTW V-8s have more torque at low end because at high end they don't breath
>right, they are able to suck in air at lower rpms better (still not good)...
>ever look at the intake system on a V8, then compare it to a 1.8 JH, the V-8
>takes are through about 5-6 turns before it gets used, the JH manifold is
>almost an intake ram setup, straight to the valves.



Uh, not quite. :)  You probably haven't driven a V8 in a while. :)  I can 
pretty much assure you that Ferrari V8s have no problems breathing at 
high-rpms.

Like TBerk said, the reason you get more low-end torque with more cylinders 
is because of the number of cylinders firing per rotation of the crank.  In 
fact, he was wrong. :)  A 4-cylinder will only have *2* power strokes per 
rotation of the crank, not 4.  A V8 will have double that, i.e. 4.

Therefore, a 4-cylinder at 4000rpm is making as many power strokes per unit 
time (minute, second, whatever), as a V8 at 2000rpm.  Therefore, the V8 
will naturally have more torque at the low-end.

Now, you're also neglecting displacement.  If you had 2 2.0 liter engines, 
one was a 4-cylinder and one a V8.  Each had exhaust and intake systems 
proportional to their breathing requirements.   What would happen 
then?  Well, at low rpms, the V8 would be considerably more powerful than 
the 4-cylinder.  However, at high rpms, the 4 cylinder's output would come 
close to, and maybe even surpass, the output of the V8.  The reason being 
that the internal friction of a V8 is considerably more than the 
4-cylinder.  Whereas you might get the 4-banger to rev to 6000rpm easily, 
the internal friction of the V8 might be so great that it doesn't make any 
power above 5000.

Of course, this was an example using a small engine.  If you were comparing 
a 5.0l 4-cylinder and a 5.0l 8-cylinder, the 8 would most likely do better 
because of the enormous size of the 4-cylinder's pistons (and the resulting 
mixture problems, etc).

Back to the point, the reason most (AMERICAN) V8s tend to run out of breath 
at high rpm is because they're designed that way -- to have gobs and gobs 
of low-end torque.  Drivers of these cars aren't the rev-happy screaming 
engine freaks that we are -- they want to squirt off the line and 
accelerate like a jet propelled craft.

And if you still think V8s have to have a lot of low-end torque, go drive a 
BMW 740i on a used car lot.  In typical BMW fashion, it's tuned for 
high-rpm screaming Autobahn assaults... and it's a dog before 4000rpm.

Jason





----------
1987 Scirocco 16v
1989 Mercedes 190E Sport Euro


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