plug recos. for high compression 418

donraye · #1 (**permalink**) 01-14-2009, 11:12 PM

I am looking for some recomendations for what plugs to run in my 418 stroker. It has a relatively high compression ratio around 11.1:1 and I think a cooler plug would be pfreferred for detonation avoidance. I was actually going to use a thicker head gasket to lower the compression down to around 10.6:1 but now I've been told that a thicker gasket might actually increase the chances of detonation as the engine tolerates detonation best in the
.035 to .045 deck range. so the .040 gasket would be the best choice with my 0 decked block.
Any recommendation out there?

RICK LAKE · #2 (**permalink**) 01-15-2009, 04:08 AM

donraye The best info I can give you is to go to a dyno shop with a couple sets of spark plugs and run it. What igintion system are you running? If you look for some of the old threads here on CC there was one with reading the spark plugs and telling you about the heat range. Color and heat range on the bridge. Also gap is very important on the motor. Start with the spec from the motor when it was stock, then go up or down .003"-.005" and read the plugs. Buy a knock sensor monitor that screws into the block and has the LED scale readout. Summit or Jegs sales them. Rick L. Ps I not trying to be smart with the answer but EVERY MOTOR has different needs and wants.

Just like a woman.

Rick L.

blykins · #3 (**permalink**) 01-15-2009, 04:31 AM

You could get away with a little thicker gasket. It's not optimum, as a zero deck with .040" quench distance is the number to shoot for in my book....but it's not going hurt anything at all to run .050" quench or a tad over.

How much would a .010" thicker gasket drop your SCR?

Rick Parker · #4 (**permalink**) 01-15-2009, 08:54 AM

The coldest plug will only be needed in a consistant WOT track situation. Find the series plug for your heads and if they are an Aluminum head, start with 2 steps colder than the recomended (from head manufacturer) plug. It is very easy to get TOO cold of a plug installed. If Iron heads, 1 step Colder. Keep an eye on them initially. This compression is not extreme by any means. Like it or not, 99% of your running is with the throttle plates "barely cracked"