Camshaft timing together with cylinder head design determine how much power an
engine develops and where in the RPM range it is. As for the cam, you tune it
by changing how long it holds the valves open, how high it opens them, exactly
when it opens and closes them, and the period of overlap when the intakes and
exhausts are open at the same time. Basically, it is impossible to have an
engine that makes a lot of horsepower and has a lot of low end torque at the
same time. You make top end horsepower by having a lot of open duration and by
having a wide lobe seperation angle. You can add further to this by retarding
the cam timing a few degrees. You make low end torque by doing the opposite.
You have less open duration, a narrower lobe separation angle, and you can add a
little more torque by advancing the cam timing a few degrees. How much you
open the valves helps both, but as valve lifts increase, valve train reliability
decreases.
If you are tuning a drag race engine, you can forget about compromising and go
for as much horsepower as you can get. But for any kind or road or oval racing,
you are going to need some torque to get you out of the corners. This means you
must make compromises with you cam specs. You have to be willing to trade some
straightaway horespower to make the power band wider. And this of course
depends a lot on your transmission. Do you have a 4,5, or 6 speed trans? What
is the lowest speed corner? What is the fastest straightaway speed? Knowing
this, plus your transmission constraint, you will be able to pick a cam grind
that alows you to keep the engine in the power band.
-Tony-
> 1) Can anyone explain and/or direct me to a site that will explain cams?
> This is the one area of the engine I don't understand. I know what the cam
> does, just not how to tune it.
Dude, you need a real auto site or a book. As for sites Iv'e unbookmarked mine
but a quick search should yeild several.
JM
