Everybody is always talking about what oil and what oil filter, so what about the spark plugs. I am going to change out my plugs in my 502Mag MPI/ EFI. Any suggestions on plugs and why?

After extensive experimentation on high boost turbo cars I have found that AC last the longest and provides the best performance. Not the AC Rapid Fire which is crap

Roby

Roby,

What about for big blower motors?

AC MR43T is what goes in my 502EFI. Have been told Rapidfire #1's work well but have not tried. Dennis Moore posted somewhere here on OSO about using a Champion plug I believe. I've always just used the AC MR43T's and have always had good luck. Buy them from NAPA and they are about 1/2 the cost of anywhere else, at least in southern Wisconsin .

I Use Ngk Number 9s On My Blower Motors But I Think Any Plug That Is Well Suited For The Job Will Work Well For You One Of The Most Important Things I Found In Any Plug If You Get The Heat Range Right Your Bound To Have A Good Working Plug . The Way I Find The Correct Plug For The Engine When We Dyno After About Two Hours Worht Of Running I'll Remove The Plugs And Inspect How Far Down The Heat Has Traveled Down The Thread I Genarally Use Three Threads For A Guideline And Its Easy To Obtain With All The Heat Range Plugs Available Today .in Ngk 1 Number Larger Is About One Thread Less Of Heat And It Also Translates To Cooler Exhaust Temps With The Same Or Even More Power With The Same Set Up Once You Get It Right.good Luck Guys Laz Mesa

NGK BR6FS Great plugs. Recommended by many.

Wanna drive your self nuts for a season trying to figure what is wrong with your engines? Try a set of SplitFire. They do not agree with Merc's ignition or something. The engines misfire and top end is a thing of the past. A/C is ok but NGK's idle and start better I think. These day with ECM you are probably better off replacing what was in there as that was what the engine's calibrations were done on right?

ngk 5671-7. 502 procharger alum. heads. Thinking about using #6 next year any comments? Greg

Doesn't matter the cu-in; the AC will work better. I have tested just about all available plugs in a GMC Syclone and Buick Grand National engines respectfully. (I use these engines as an example because they create more HP per cylinder than most supercharged big blocks) The AC plugs are the only ones that seem to survive numerous runs at above 20psi. Believe me I have tried the expensive platnum plugs and they won't make it a quarter mile w/o flaming out. I'm sure for a NA engines they're fine because they do promote an efficient burn as indicated by narrow O2 variance. The AC CR-series plugs did have a wide O2 variance with many X-counts but they do handle the boost better than any plug I have seen.

Roby

Nothing scientific, just my experience. I put the Champion RV15YC4 in my 502 carb motor this year and have been pleased. They idle great, no hesitation on takeoff after a 1/2 hour no wake zone and they look good after 25 hours. These are the plugs that champion recommends for BBC Marine motors according to their chart.