Rob C Swift wrote:
> I have a Kent "Fast Road" cam, and most
> peoples opinion is that this cam does not
> allow the valves to shut completely at idle,
> allowing unburnt fuel to pass out the exhaust.
And Shawn Loseke wrote:
>If your valves aren't fully closing, I think
>you would have a bigger problem in the way of
>burnt valves. If the valves weren't closing at
>Idle, then why they would they be closing at
>any other point. Our cars don't have variable
>valve technology....
Just as a matter of logic, I don't understand how the valves could fail to
shut at idle. If the valve train has any clearance at all, the valves are
presumably closed . . . otherwise there'd be no clearance.
Generally the valve clearance is set with the engine off, but you can also
test to see if there is _SOME_ clearance with the engine idling.
Many race cams with high duration and overlap (including my own) call for
increased valve clearance - in the neighborhood of .020" or more, so if your
car is tuned to "Haynes" specs (.010" cold) the valves may be set
incorrectly for the cam you're using.
In any event, increasing the valve clearances will cause the valves to open
later and close earlier. You might try doing that as a way of decreasing
duration and overlap - presumably reducing emission of unburned gasses.
You might also check for weak or broken valve springs.
Jim Hill
Madison WI
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