Spark plug gap....increase or decrease for more power?
Thread Starter
Pro
Joined: Aug 2001
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From: Redmond WA
Spark plug gap....increase or decrease for more power?
I have a Jacob's system in my car, as well as all the other mods you see in my sig. Jacob's recommends gapping .015 over factory gap, but there is the other school of thought that running a smaller gap will net more spark energy. I've heard that the hot cam can wreak havoc on plugs that are gapped too wide, that it will blow out the spark.
I have a new set of plugs to put in and haven't decided whether or not to over gap, under gap, or just take the middle road and do the factory recommended .050.
Thanks,
Sam
I have a new set of plugs to put in and haven't decided whether or not to over gap, under gap, or just take the middle road and do the factory recommended .050.
Thanks,
Sam
Racer
Joined: Jul 2002
Posts: 269
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From: Paris AR, USA
Re: Spark plug gap....increase or decrease for more power? (castivers)
As far as I know (which might not be too far :) ) a wider plug gap helps power, as long as your ignition system is capable of firing that gap reliably; That's why Jacobs recommends increasing it a bit. Personally, on an LT4, I'd leave it at the factory recommended setting. Higher cylinder pressures require smaller plug gaps. You've got a high comp ratio. While the hot cam might lower your overall cylinder pressure a bit at low rpm, at high rpm (which is more difficult for the ignition system to handle anyway) you'll most likely have higher cylinder pressure (the reason you'd make more power).
As mentioned above, cut-back ground electrodes might be worth a couple hp. It will reduce plug life a bit and I'm not sure how much of a PITA changing spark plugs is on an LT4-- so you might weigh that out.
My .02 :cheers:
Jason
As mentioned above, cut-back ground electrodes might be worth a couple hp. It will reduce plug life a bit and I'm not sure how much of a PITA changing spark plugs is on an LT4-- so you might weigh that out.
My .02 :cheers:
Jason
Race Director
Joined: May 2001
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Re: Spark plug gap....increase or decrease for more power? (LT4Sam)
I don't think you'll really see enough difference to make it worth messing with it. I've got a Hot Cam and an MSD igntion system, digital 6+, MSD blaster coil, and MSD wires. I still gapped the plugs at like .045
I'm 100% assured that it's gonna fire every time. In general run the largest gap you can get away with, but this way I've bought myself a little room as the plugs wear down. MSD recommends around .060 for my comp ratio, but it also says that every car is different and you'll just have to experiment with it. Remember some plugs aren't made for a large gap and it will change the geometry of the electrode dramatically, that's the biggest reason I gapped mine small, it didn't look right having them gapped at .060
I'm 100% assured that it's gonna fire every time. In general run the largest gap you can get away with, but this way I've bought myself a little room as the plugs wear down. MSD recommends around .060 for my comp ratio, but it also says that every car is different and you'll just have to experiment with it. Remember some plugs aren't made for a large gap and it will change the geometry of the electrode dramatically, that's the biggest reason I gapped mine small, it didn't look right having them gapped at .060
Burning Brakes
Joined: Oct 2002
Posts: 1,152
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From: Wichita KS
Re: Spark plug gap....increase or decrease for more power? (Nathan Plemons)
Keep this in mind, I took a certified micrometer recently & checked the thickness on one of those over the counter spark plug gap setter/checker, the .050 wire checked .044, and don't even think about the blade type they are even worse. I finally found a good snap-on wire type gauge & double checked it prior to buying it with my Mic. I had that other gauge for years, who knows how many plugs I miss-gapped. Just never thought about checking it. Just a little food for thought. :seeya
Team Owner
Joined: Sep 2001
Posts: 62,127
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: Spark plug gap....increase or decrease for more power? (KYVette90)
I know it helps a little bit on L98s, but maybe not so much for the LT1/4 engines.
Drifting
Joined: Sep 2002
Posts: 1,269
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From: Swanzey N. H.
Re: Spark plug gap....increase or decrease for more power? (LT4Sam)
I wouldn't use too wide of a gap. Most plugs get wider over time, I never heard of one lessening its gap. I would leave them at the stock setting.
On my Harley, I have vortexed heads, which are small wedges installed on the intake side that cause more turbulance to help spread the fuel/air more evenly. It comes in at a greater rate of speed, therefore, my plug gap has been lessened so it won't blow out the spark. Same with a turbo, if the boost is turned up, the incoming fuel/air comes in at a greater rate of speed, and the gap should be lessened. So what I'm trying to say is if your fuel/air mixture ISN'T coming in at a greater rate of speed, DON'T lessen your gap. :cheers:
On my Harley, I have vortexed heads, which are small wedges installed on the intake side that cause more turbulance to help spread the fuel/air more evenly. It comes in at a greater rate of speed, therefore, my plug gap has been lessened so it won't blow out the spark. Same with a turbo, if the boost is turned up, the incoming fuel/air comes in at a greater rate of speed, and the gap should be lessened. So what I'm trying to say is if your fuel/air mixture ISN'T coming in at a greater rate of speed, DON'T lessen your gap. :cheers:
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From: Northern tip of Virginia
Re: Spark plug gap....increase or decrease for more power? (Jim Holbrook)
I would also suggest leaving them at stock settigs.......................
BUT..................
In theory, a wider gap wold ive more power.... "more" spark.
As mentioned earlier..... cut plugs are a "trick" that might offer the biggest gain.
Set gap as normal,,,, then cut the wire at or near the bend, then dress up the sharp "edges" with emery cloth.
The thinking here is that now, your spark will be totaly exposed and MUCH more efficient.
The ONLY downside that Ive ever heard is shorter plug life, and that doesnt matter to anyone thats serious about tuning anyway. :D
BUT..................
In theory, a wider gap wold ive more power.... "more" spark.
As mentioned earlier..... cut plugs are a "trick" that might offer the biggest gain.
Set gap as normal,,,, then cut the wire at or near the bend, then dress up the sharp "edges" with emery cloth.
The thinking here is that now, your spark will be totaly exposed and MUCH more efficient.
The ONLY downside that Ive ever heard is shorter plug life, and that doesnt matter to anyone thats serious about tuning anyway. :D
