Piston to spark plug clearance

[1972_911T]

Whats the minimum piston to spark plug electrode clearance it is safe to run?

Steve

[3.2 CAB]

I am not sure on the clearance issues, because it really depends on several things, like domed pistons, relief cut pistons, etc. Something that we used to due when I was drag racing, we would index the spark plugs to get the optimal spark direction for more complete combustion inside the cylinders. This was achieved by using various combinations of copper washers. This made sure that the spark was pointing towards the center of the combustion area, instead of possibly pointing at the cylinder wall. Good luck!!

[Eagledriver]

I would say the minimum would be the same as for head clearance, about 1mm or .040 inches. I would also say it's not critical because if you don't have enough clearance all you'll damage is the spark plug.

-Andy

[cgarr]

Unless you using something really exotic I don't see the plugs extending any beyond the bowl surface, even in our twin plugged heads.

[1972_911T]

Hi guys thanks for the input, the problem ive got is im trying to use some twin plugged heads with cis 9.8:1 domed pistons. Im having contact between the second plug and the piston as the second plug is right above the highest part of the dome. Ive got some 4mm spacers which give me about 1.5mm clearance between the top of the piston and the plug when I remove the washer off the plug so I think im asfe at that.

Steve