plug gapping for high compression piston

[rooster300ex]

i've read in atv sport mag that high compression pistons require different plug gapping then just a stock piston. i was wondering if anybody knows the plug gapping for a 300ex with a HC wiesco piston. i did a search and found something on 400ex but it doesn't have a high compression piston.

[bwamos]

I assume your just rinning the 11:1 Wiseco. If so stock gapping is fine.

If you get in the 13:1+ range you have to worry about it.. because the piston gets closer to you plug and you dont want the spark jumping to your piston.

[rooster300ex]

what is the stock gapping?

[wilkin250r]

Spark jumping to your piston? :huh

No.

It requires energy for a spark to jump across an air gap. The amount of energy depends on several factor, like the distance of the air gap, impurities in the air gap, and the density of the air.

More impurities make it harder to jump the air gap. Those impurities would be fuel molecules.

Dense air, as in higher compression, make it harder to jump the air gap.

Less distance (smaller gap), makes it easier to jump the air gap.

So, as compression increases, it is more difficult for the spark to jump across the gap. If compression increases too much, the ignition system can have trouble jumping the gap, and possibly misfire. To correct this, you would close the gap. If stock is 0.025", you might want to go down to 0.020".

In a stock engine at low compression, a gap that is too small may have trouble igniting the fuel/air mixture. Fortunately, higher compression ignites easier, because there are more fuel molecules present in the air gap, so you can get away with a smaller gap.

[86250rrider]

WELL SAID! many people do not understand this and gap larger. thus creating more problems! good job:D

[nosliw]

ive heard of oldschool hotrodders breaking the ground off the sparkplug so it grounds itself to the piston. all of course in trying to squeeze every ounce of power they can out of an engine, but would this help? problems i can see are irregular spark jump, possible damage to piston and if the spark can even jump that big of a gap.

just thought id throw this in here to see waht yall have to say

[raptor02r]

to answer this guys question. gap it to .35

[wilkin250r]

First off, .35 is larger than a quarter inch. You want .035.

Cutting the ground off the spark plug will not jump to the piston. It will jump the the edge of the spark plug. This is most common for drag racers, as such a large gap makes for very short spark plug life.

[nosliw]

Originally posted by wilkin250r
First off, .35 is larger than a quarter inch. You want .035.

Cutting the ground off the spark plug will not jump to the piston. It will jump the the edge of the spark plug. This is most common for drag racers, as such a large gap makes for very short spark plug life.


oh, thanks for clarifying that man.