What spark plugs are you guys running in a relatively stock 502. I do have a MSD box and Lightning Headers.

I run NGK BR6FS.

NGK seems to be the plug of choice for many these days.

I have been using AC Rapid fire 1, the plugs are expensive but forth it, why you ask? It will clean up your transom. The plug extends deeper into the combustion chamber. Also you will be able to use them for two seasons.

What plugs are you using in the HP500EFI's?

save your money run AC R43TS

I installed the rapid fires this spring on my 502's because of the postive posts for them. My transom is always black. I will replace them with the Merc spec'd AC plugs when the time comes.

if you read Dennis Moore's book you will realize that what makes all thee plugs similar are the extended tips, I have used the AC R43TS on all my boats 454, 454 w/blower, now 502s and never get any black crap.

They are much cheaper than the "novelty" plugs too and do the same job.

Shooter what about page 177 Champion RV15YC4 EX.long projected nose or AC #R43LTSM

I think the LTSM is a different size plug, where the 43TS just has a long tip. No sure though. Always used the AC myself.