plug gap, increase or reduce?

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Rapid Robert

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360 circle track engine. would I gain by going up or down from the std .035" gap? std mopar dist/pertronix race coil/module. thank you for your time. RR
 
I put the plugs at around 38-40, I like the crack sound it makes and also to make sure that gas get plenty of ignition.
 
Most ignitions don’t do much more with more than .035, other than make it harder on the plug wires, cap and rotor.
 
Hotter the spark the coil and ignition module will throw, the more gap you can run. I’m not knowledgeable about pertronix gear.
 
You can side gap the plugs, but as mentioned, I still wouldn't go more than about .035 - .040.
 
You can side gap the plugs, but as mentioned, I still wouldn't go more than about .035 - .040.

I agree with this for now, not knowing how hot the pertronix is. Gotta read those plugs after a heat run. I'd have to go back and read your posts on the combo regarding a standard plug verses a projected tip.
 
A old Sprint car racer told me run as much Gap as your ignition will support but those guys were running magnetos. 35 to 40 is always been the sweet spot for me. Just an MSD blaster coil chrome box and Mopar high performance distributor.
 
Robert, this is an area worth experimenting on. Widen the gap until power or lap time falls off. Better off .005 small than .005 to big.
 
I have been running the Accel Square top supercoil since 2002 I think. The plugs were already 2 years old then, and are still in the engine today. They were re-gapped to .045 in 2004, the last time I freshened that engine. They have over 100,000 miles on them at this time.
I have not looked at the gaps since 2004.
It would be interesting to see the gaps today, but that ain't gonna happen lol.
I love that coil, best I ever bought.

Delco Plugs for HEI Chevy's used to come pre-gapped to around .080; IIRC
 
Yep, some GM HEI engines had 0.080" plug gaps.
The most important component is the coil. It should be an E core for max spark energy. I run 0.070" gaps, as does my mate who races, he goes to 6500 rpm with a MSD HEI 4 pin module & #8207 E core coil.
 
I have been running the Accel Square top supercoil since 2002 I think. The plugs were already 2 years old then, and are still in the engine today. They were re-gapped to .045 in 2004, the last time I freshened that engine. They have over 100,000 miles on them at this time.
I have not looked at the gaps since 2004.
It would be interesting to see the gaps today, but that ain't gonna happen lol.
I love that coil, best I ever bought.

Delco Plugs for HEI Chevy's used to come pre-gapped to around .080; IIRC
I'm sure that those plugs are shot. I'm not saying that you don't have them with the mileage you claim it's that I've never seen a plug that much of a electrode left with over 60k on them
 
The really large gaps generally came with HEI ignitions running Platinum/Iridium plugs. Other wise electrode life if shortened.
 
Nooooooooooooooo,
Plat/Irid plugs were not around in the 1970s when HEI made it's debut.
 
We are talking about .060-.080 gaps. also not in the 70's... No body said when HEI it made its debut. HEI with precious metal electrodes, reread it. Gaps got wider when the precious metal electrodes came out.
 
We are talking about .060-.080 gaps. also not in the 70's... No body said when HEI it made its debut. HEI with precious metal electrodes, reread it. Gaps got wider when the precious metal electrodes came out.
Buick had some plug gap specs at .080 in the 1970s. Cadillac also used a .120 gap for a short time also in the 1970s.
 
I ran .045 was very crisp coming out of corner running rich with long tipped plugs, run good 8mm wires
 
I will be running a pertronix HEI type race Ecoil and with their race module mounted under the OE Mopar dist with a good curve
 
The primary determinant is the combustion conditions. Chamber design, squish, compression, fuel type, fuel dispersion and vaporization...
The second determinant is the ignition. If it can initiate a spark across a larger gap - and then provide the energy to maintain it. A larger, stronger spark can develop a stronger kernel of flame.
The gap that produces the best results in your racing engine will be the one that produces a sufficiently large and strong enough kernal for the rest of the fuel to flame completely and consistantly. When going for larger gaps, the ability of the ignition system to provide the voltage and energy can become a limitation.
 
IMO Go up in increments. See how it goes. Pump fuel or race fuel? Race fuel shouldn't need as much help and will be more consistant.
 
I would think that this is a pretty hefty ign (coil/module) & yes that a larger kernel would be a bennie but I've seen several sources (jacobs ign comes to mind) that recommended a smaller gap for power/racing which is confusing. RR. EDIT 9-1 CR & we can use pump or racing gas either one (which would you recommend?)
 
I would think that this is a pretty hefty ign (coil/module) & yes that a larger kernel would be a bennie but I've seen several sources (jacobs ign comes to mind) that recommended a smaller gap for power/racing which is confusing. RR
The advantage of the HEI is that its more capable (or should be) in providing the voltage to jump a more difficult gap and maintain that spark once it begins. It also should be able to adjust the coil current at high rpm. In other words the ignition system should not be a limitation if you want to try .040 or .045" gaps.
For starting point, I'd go with the guys here who have run similar engines to yours in circle track. The combustion chamber, valve events, etc etc are all going to be closest to what you built. We can be pretty sure Jacobs didn't do roundy round with mopar 360s and an HEI.
 
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