Compression head spark plug

WRONG PLUG I think a 6 is to hot . Try cooler plug. This is what you need is a3/4' drop plug not a 1/2' drop. So get yourself a NGK B7ES, or even cooler B8ES, even cooler a B9ES or the COLDEST B10ES plugs.

All NGK plugs for these are longer than stock (which is like a high compression head and cheaper) and in most cases should NOT be used with a high compression heads but it's easy to test.
Put it in and rotate you piston to TDC, if it hits the plug dongle you need to run a stock length plug.

The heat number index (5,6,7,8) is just the amount of heat sinking material in the plug itself, not it's length.



The higher the number the more heat that is removed from the engine, run this as high as you can until your engine is not hot enough to keep your plug from fouling.

I live in the desert so 7 and 8's are common because it's hot.
In the cold where your engine can't seem to 'warm up' use a lower number to keep the engine heat in enough to warm up and not foul your plug.

AGAIN, TEMP RANGE HAS NOTHING TO DO WITH PLUG LEGNTH!

I gave you the correct plugs.

part of the compression ratio is timing but some will disagree. That not so much a theory when the engine fires 15 degree advance. That's firing @ 85 % fuel compression and worse yet the compression stroke has not fully completed. I'd tell you serve self and add a thick washer on the end of that spark plug if anything is worthy of the conversation......