Spark Plug Gap with MSD 6A

[LocuMob]

In trying to figure out the best gap for my plugs on the Polara. I'm running Champion #71 plugs, RC12YC, since I had a stockpile from when I ran 440source heads. I've been gapping th plugs at factory .030" the FSM calls for. I guess I can go up to .050" with the MSD. Does it matter? Should I be using a stock plug? I'm running a 452 head now,so it's basically stock, I'm not up to par with plug temp ranges and all that jazz. I just had a bunch of #7 plugs laying around and I'm a cheap *** so I used what I had. Now I'm out and wondering what I should buy next. Tell me how to.spend my money! Thanks.

Scott

 

[Big_John]

I've run .050 gap with the MSD and it works quite well.

The thought is that the plug has to have more energy to jump the gap and that should allow for a hotter spark. One benefit from that is it makes the plug less sensitive to fouling.

Heat range you will have to figure out on your own... The intrawebs is full of info on how to do that, but it's basically the coldest plug you can run without fouling. I'd run the ones you have to start with.

 

[LocuMob]

I've run .050 gap with the MSD and it works quite well.

The thought is that the plug has to have more energy to jump the gap and that should allow for a hotter spark. One benefit from that is it makes the plug less sensitive to fouling.

Heat range you will have to figure out on your own... The intrawebs is full of info on how to do that, but it's basically the coldest plug you can run without fouling. I'd run the ones you have to start with.

That's the plan, I'm on the last bunch, I'm too lazy to look up heat ranges, I did a while back but forgot it all.

 

[1978 NYB]

The bigger the gap the better and hotter the spark.

 

[C Body Bob]

On my old drag car i had installed a MSD to replace the Chrysler Electronic i had added years earlier. I ran .32 gap with the Chrysler system. On the MSD it ran MUCH better. Noticeable seat of the pants. So I decided to move the gap to .50 and the car was harder to start & didn't ET as good. So I dropped it back to .38 for a happy medium & it ran great again. The ET returned & it started easier with a lot of timing & I got 3 seasons on a set of Champions. Before the MSD box I had to replace them every winter after the season was over.

 

[Yatzee]

In trying to figure out the best gap for my plugs on the Polara. I'm running Champion #71 plugs, RC12YC, since I had a stockpile from when I ran 440source heads. I've been gapping th plugs at factory .030" the FSM calls for. I guess I can go up to .050" with the MSD. Does it matter? Should I be using a stock plug? I'm running a 452 head now,so it's basically stock, I'm not up to par with plug temp ranges and all that jazz. I just had a bunch of #7 plugs laying around and I'm a cheap *** so I used what I had. Now I'm out and wondering what I should buy next. Tell me how to.spend my money! Thanks.

Scott

.045 is perfect and while your at it try a set of Motocraft plugs of the same reach. They're way superior to Champion and not fussy on heat ranges. They'll last three times as long so if your cheap, the performance and longevity makes them a real bargain. Most knowledgeable people using MSD units prefer these or NGK's over Champion.

 

[pomonamissel]

run mine at .035 gap with no issues . ran the gap all over the range from .06 thru .03 in the mw car , but .032-.035 ran the best times . and yes i ran autolites over champions in the racer . but autolites leak by the ceramic cores i've noted , some blacking soit just passed the hex the white ceramic . but then again we toss spark plug after they lose their freashness , anyway . use them in the street rides . oh ya the mw car has two separate ign's , a msd and a chrome chrysler box , and i can switch between them . that was a bit of wiring madness and switches . just to prove the ign's problems . and the chrysler box takes more amps to rum then the msd if anyone needs that info , it was just a battery draw system until i put a charging system on it .

 

[Welder guy]

run mine at .035 gap with no issues . ran the gap all over the range from .06 thru .03 in the mw car , but .032-.035 ran the best times . and yes i ran autolites over champions in the racer . but autolites leak by the ceramic cores i've noted , some blacking soit just passed the hex the white ceramic . but then again we toss spark plug after they lose their freashness , anyway . use them in the street rides . oh ya the mw car has two separate ign's , a msd and a chrome chrysler box , and i can switch between them . that was a bit of wiring madness and switches . just to prove the ign's problems . and the chrysler box takes more amps to rum then the msd if anyone needs that info , it was just a battery draw system until i put a charging system on it .

Thanks for your post that is some interesting info. I'm not a race car driver so I'm trying to understand this. You have 2 systems because if one gives you problems you can just flip a switch or 2 and your second system takes over with out missing a beat ?

 

[LocuMob]

Thanks for your post that is some interesting info. I'm not a race car driver so I'm trying to understand this. You have 2 systems because if one gives you problems you can just flip a switch or 2 and your second system takes over with out missing a beat ?

I think he did it to verify a system was /was not working properly.

 

[pomonamissel]

ya its a tester , but its a back up as well . from one to the other . i run the msd as a primary system . but there not fool proof and sometimes break down . and its a few days turn around for msd service to repair . so if its a must to run the car , i can drive rather then push it . but the main reason was for proving out ign issues or something else making it right . not something that a street car needs . and i run it street/strip .

 

[LocuMob]

Update:

I swapped plugs and gapped them at .040. Car ran fine all day. Put on about 150 miles or so, it was a great day for a drive. I'm happy with the way the car performed, it was responsive and didn't give me any problem, not that it really does, but it seemed a little better. Now on to my exhaust!

 

[CBODY67]

The basic 383 2bbl plug was J14Y, gapped at .035" All plugs gapped to .035" back then. The 383 4bbl was usually J10Y, gapped to .035". The 400 2bbl used J13Y, .035" with the Chry electronic ignition.

Strongly concur that the coolest plug that doesn't foul in how you normally drive. As for gap with the MSD 6AL, I think they used to say that you could run gaps to .060", but others noted that when you got past .045", there was no power to be gained. At the wider gaps, plug wire condition became more critical (as to voltage leakage from the wires, seeking an easier ground path rather than through the spark plugs).

Also strongly concur on the Motorcraft plugs being longer-lasting plugs, in the 'normal' style spark plugs. Only thing better is NGK Iridiums. For general heat range crosses between brands, you might lookup an application in RockAuto and see them there. Otherwise, the particular brand plugs' website.

The wider gap is supposed to allow for more spark exposure to the mixture in the combustion chamber. But, as mentioned, there is a limit to where the benefits start plateauing.

CBODY67