Egil Kvaleberg writes:
> No, don't even think about it. If the gap is set to tight, you'll run
> a significant risk of burning your exhaust valves. If set too lose, the
> engine will become noisy and you will significantly increase wear in
> the valve train. Not that I quite see the point in a lose fit anyhow,
> it simply gives an overall decrease in power by reducing the lift and
> duration.
I agree on all these points. A lose fit will gain you better
emissions, at the cost of performance as you point out.
> The optimal gap for any cam will depend on details in the actual cam
> profile.
WHY?!? :-) This is the question I'd like to have the answer to. Why
is a hot cam set to a clearance of say .025 instead of .010 stock?
One answer I got was because of the ramp of the cam. This makes sense
as a steeper ramp on the cam, the more effort it will take to open the
valve. Thus we get a "head start" up the ramp before encountering the
spring pressure of the valve. There must be more than this.
My theory is that cam manufactures can "tweak" the cam by using
different valve lash settings. This is far more acurate than the
grind on the cam, and can be adjusted. It also takes place after the
additional rocker ratio is calculated into the overall valve lift,
which adds to the acuracy of the valve timing. But I'm no expert,
just making guesses...
> If you want to play around with your cam, you can modify the overall
> timing by adjusting the timing chain. Early timing usually improves the
> top end, late timing increases torque at low revs. Don't overdo it,
> though.
Been there, done that. The problem with my old cam was the machine
shop misground the cam. I know as I carefully measured it. It wasn't
even close to what it should have been. Just installed the new one
(close to stock) and the idle is close to perfect. More on this story
later... :-)
-Scotty
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