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View Full Version : Spark Plug Gap for Electric Ign?


scottpiper27
06-27-2012, 08:14 PM
Hello All - I have a 1990 Prostar 190 Indmar 351w. I have finally tossed the old points distributor and just installed a pertronix flamethrower elec. distributor and also got a new coil, plugs and wires to make it all nice and new. I'm a bit lost on the proper gap for the plugs.

I have read other posts, but my mechanic threw a curve ball at me. According to the owners manual, the man at the marine supply store where I bought them, and other posts, It would appear that the gap is unchanged at .035. However, my mechanic did some research and found some literature that says the gap changes to .06 on a 351w that uses elec. ign. I would just tell him he's wrong, but he is a very experienced mechanic who specializes in 351's and is very trustworthy and skilled. I didn't find out exactly where he got that info.

Anybody know for sure, or know who I can contact to get a for sure number?

Thanks - Scott - keep slalom alive

Philscbx
06-27-2012, 08:29 PM
The Gap is simply mis applied to the wrong item.

Gap for the Plugs are .035.

Gap for the electronic Ign modual probably is .006

east tx skier
06-27-2012, 08:35 PM
My 93 MC with 351 HO had EI from the factory and the manual said 0.035.

j.mccreight@hotmail.com
06-27-2012, 09:48 PM
Most aftermarket units state to use factory spark plug gap setting in this case .035. In a racing setting they advise to enlarge .005 at a time reading plugs as you go, but they are also using a msd or hifire box of some sort to enhance spark intensity and a lot more horsepower. Also the wider the gap you have a greater chance of misfire. If your setup is bone stock other than the ei change stick with .035, if you have changed heads, intake, camshaft with msd good wires then you could possibly go to .045. I had a drag racing buddy with a super charged 351w in a mustang with about 800 horse and he gaps his at .018 when he closed the gap from .045 he picked up 30 hp on a dyno. I would never go to .060 on a stocker.

scottpiper27
06-27-2012, 11:15 PM
Thanks a million guys - sticking with .035. And thanks for such a quick reply, hoping to be out on my ski before the 4th and this helps a lot.

east tx skier
06-28-2012, 01:26 PM
Most aftermarket units state to use factory spark plug gap setting in this case .035. In a racing setting they advise to enlarge .005 at a time reading plugs as you go, but they are also using a msd or hifire box of some sort to enhance spark intensity and a lot more horsepower. Also the wider the gap you have a greater chance of misfire. If your setup is bone stock other than the ei change stick with .035, if you have changed heads, intake, camshaft with msd good wires then you could possibly go to .045. I had a drag racing buddy with a super charged 351w in a mustang with about 800 horse and he gaps his at .018 when he closed the gap from .045 he picked up 30 hp on a dyno. I would never go to .060 on a stocker.

My PCM 351 GT40 runs 0.045 without issue. This is the recommended setting from PCM for their 351s.

j.mccreight@hotmail.com
06-29-2012, 11:06 PM
My PCM 351 GT40 runs 0.045 without issue. This is the recommended setting from PCM for their 351s.

Your also factory 70 horse hotter, just sayin;)

east tx skier
06-30-2012, 10:14 AM
PCM recommends that gap on all of their 351st if I recall correctly.

pbgbottle
06-30-2012, 11:35 AM
I am using .040. On my 88 351 indmar
With the flame thrower II. I have had no issues. I Also use the flame thrower low resistance coil. FWIW.