Tolerance Level - short/long PTV clearance
- Thread starter rdubb17
- Start date
.080" for the intake valve and .100" for the exhaust valve is the usual maximum closeness you should allow.
Some cam vendors say .100"/.120".
The exhaust valve needs a little more due to expansion because of the more direct heat that passes over it.
As the rpm increases, the tolerance level needs to be increased.
The above requirements is good for a 6,000 RPM engine.
Advancing or Retarding the camshaft can gain you a bit...although it compromises your performance and powerband.
Advancing the timing opens the intake sooner and closes the exhaust sooner. That will gain you some clearance on the exhaust valve, but you will lose clearance on the intake valve. Retarding the cam causes the timing to open the intake valve later, and closes the exhaust later. You'll gain clearance on the intake, and lose clearance on the exhaust. So changing the cam timing won't result in increasing clearance on both valves. So you need to see which one you need most...
Adjusting either way can shift the powerband 200 rpm that direction...
Some cam vendors say .100"/.120".
The exhaust valve needs a little more due to expansion because of the more direct heat that passes over it.
As the rpm increases, the tolerance level needs to be increased.
The above requirements is good for a 6,000 RPM engine.
Advancing or Retarding the camshaft can gain you a bit...although it compromises your performance and powerband.
Advancing the timing opens the intake sooner and closes the exhaust sooner. That will gain you some clearance on the exhaust valve, but you will lose clearance on the intake valve. Retarding the cam causes the timing to open the intake valve later, and closes the exhaust later. You'll gain clearance on the intake, and lose clearance on the exhaust. So changing the cam timing won't result in increasing clearance on both valves. So you need to see which one you need most...
Adjusting either way can shift the powerband 200 rpm that direction...
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