Spark plug gap

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MomsDuster

MomsDuster

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I’ve got a tuning question. I’ve always just gone to the book when gapping spark plugs. But then I’ve always had stock cars. So what factors in to the proper spark plug gap on performance engines?
 
talk'n with a guy that had a mild 440 in a Dart at the drag strip. He was running 10.50's and his champions were gapped at .035.

Some will widen the gap with a "hotter" spark system, maybe to .045.
 
If you get the book written Jacobs he covers quite a bit on plug gap. If you have enough ignition and if you have good enough wires and the cap and rotor are in shape, you can open the gap and help with combustion.

As I've said since I was still in my late teens...most cars are ignition defficent, unless they are dead stock. It's easy to tell. Especially if you are on the dyno. Just open the gap until power falls off. If you can't get much over .040 without losing power you can use more ignition. An MSD 6 is notoriously weak. The Crane when you could get it and the Mallory 685 box were much better. Neither one understood advertising very well.

Wish I would have done some testing on the Jacobs stuff.
 
Hey Mom, for what it's worth I run the MSD 6 Al. It is an older unit, maybe 10 years old. I have a basic Mopar distributor. My coil is from Pertronix. This coil is supposed to put out 60,000 volts. I have seen this thing make sparks. Mom, this coil makes freeking lightning. My gaps are set at .045
 
MomsDuster said:
I’ve got a tuning question. I’ve always just gone to the book when gapping spark plugs. But then I’ve always had stock cars. So what factors in to the proper spark plug gap on performance engines?
Click to expand...
Spark plug gap is conditional on how much total energy the ignition coil puts out. Energy, not voltage. The wider the spark plug gap the higher voltage needs to build up to ionize the fuel-air mixture in the spark plug gap. Once the mixture is ionized current can flow across the plug gap. The time the current is flowing across the plug gap is the burn time. Typically, 1 to 1-1/2 milli-seconds.

All else being equal, the more voltage it takes to ionize the fuel mixture the less energy is available to sustain the burn time, and vice versa. The less voltage required to ionizer the mixture the more is available for burn time. You want enough burn time that the fuel-air mixture in the combustion chamber is exhausted.

Obviously, the fuel-air mixture plays into this as well. A richer mixture in the plug gap is easier to ionize. You can see that there are multiple variables involved. So, it depends.
 
Rustedwrench said:
Spark plug gap is conditional on how much total energy the ignition coil puts out. Energy, not voltage. The wider the spark plug gap the higher voltage needs to build up to ionize the fuel-air mixture in the spark plug gap. Once the mixture is ionized current can flow across the plug gap. The time the current is flowing across the plug gap is the burn time. Typically, 1 to 1-1/2 milli-seconds.

All else being equal, the more voltage it takes to ionize the fuel mixture the less energy is available to sustain the burn time, and vice versa. The less voltage required to ionizer the mixture the more is available for burn time. You want enough burn time that the fuel-air mixture in the combustion chamber is exhausted.

Obviously, the fuel-air mixture plays into this as well. A richer mixture in the plug gap is easier to ionize. You can see that there are multiple variables involved. So, it depends.
Click to expand...


All true. You just say it better than I do!

There are times when no matter what ignition you have you have to close the gap down. Big nitrous, blowers and turbos are hard to get lit, even with the big boxes.

Magnetos will fire about anything but they always use a relatively small gap, even in N/A usage.
 
I'm running the Pertronix Igniter 3 look a like Distributor, Flame Thrower 3 coil and wires and a .045 gap on the NGK plugs and this system is flawless. Timing is set at 36 total and the touch of the key and it fires right up hot or cold. Best part is no more chrome box or ballast resister to crap out on me.
 
yellow rose said:
If you get the book written Jacobs he covers quite a bit on plug gap. If you have enough ignition and if you have good enough wires and the cap and rotor are in shape, you can open the gap and help with combustion.

As I've said since I was still in my late teens...most cars are ignition defficent, unless they are dead stock. It's easy to tell. Especially if you are on the dyno. Just open the gap until power falls off. If you can't get much over .040 without losing power you can use more ignition. An MSD 6 is notoriously weak. The Crane when you could get it and the Mallory 685 box were much better. Neither one understood advertising very well.

Wish I would have done some testing on the Jacobs stuff.
Click to expand...
I did the Jacobs stufff. Bought their adverting hook,line, and sinker. Got me one of their topline CDI multistrikes and matching E-core coil. Ran it with the same .042 gaps as the Orange box had been blasting (RN12YC Coppers). It didn't seem to run any different, and then one day about a month later,when the CDI box crapped out 20 miles from home, I was glad I had left the old system on standby. Ten minutes later I was rolling. But the Orange box was not happy with the Ecore coil.
Then I remembered that the Jacobs dial-back Timing device under my dash, had an amp in it, so I did some rewiring and it sorta ran better. So then I ordered up an Accell Sq-top, out of the Mopar catalog and two days or so later, wired that in. So now the only Jacobs part left is the amp, and it has worked flawlessly since ~2002.
Ok now the big deal;
Those plugs were regapped to .042 in 2004, the last year I took that 367 apart. At that time the plugs were already from November 1999. Now in June of 2004 I got it into my head to track that car, and pulled the plugs out, cuz you know, they had a lotta miles on them since 99. Well, they looked so good, I regapped them to .050 and rolled them back in. Got to the track, ran 93 in the Eighth,shifting at 7000 on a 230 cam, and went home.
Ok so those plugs are still in there today, never having been out since. The new ones I bought for the track-event, are still in the trunk....... you know, just in case,lol.
Am I hooked on that big fat Yellow beast of a coil? You better believe it,lol. Who knows after all these years, what my plug gaps look like, no man that's for sure.

BTW; I still have that just-warrantied Jacob'S CDI box, still in the box they shipped it back to me in, and slightly used E-core coil .........
 
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