Thread: Spark plug gap

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Also here is another thought, change your cam duration and you also change your spark timing, I am talking amount of time for the spark to jump the gap here ?

not so much... the cam duration will change valve time but it wont change the electrical circuit, it will somewhat change cylinder tempature and wether the valve is fully closed when your plug is firing, which is ok as long as the valve will be closed by the time full combustion occurs, but fuel combustion only takes 4ms, under normal compression, which is like nothing but is also why higher and higher performance applications require more compression and more combustable type fuels....

remember one thing the GM HEI units where designed initally to use a gap up to .060 inches and the gap can be used to change the timing up to 2 degrees (either direction ) as when I went to school for briggs this is how we adjusted the timing on those little motors as the magnetos are fixed to the motor frame and when you ran kero it was crutial ,

[QUOTE=thesals]not so much... the cam duration will change valve time but it wont change the electrical circuit,

Think abouty that statement for a minute. I agree a longer duration cam will definitely close the intake valve at a later time.... when the piston is further up the bore. Since the piston is furthur up the bore, what does this do to cylinder volume ? It decreases it because compression cannot happen untill the intake valve is shut. So with less volume of fuel air mix to compress the dynamic compression ratio is lower. Subsequently if you put a shorter duration camshaft in the dynamic compression ratio will be higher. So these pressure variations will have an effect on spark timing due to the density/ resistance to the compessed air at time of ignition. It will not be great but the variance is there.