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Old 10-25-2012, 11:16 AM   #1
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quick ? for you gt40 guys

What are y'all gapping your spark plugs at?
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Old 10-25-2012, 12:06 PM   #2
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What are y'all gapping your spark plugs at?
Mines at .052
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Old 10-25-2012, 03:32 PM   #3
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Mines at .052
me to, even though i dont have gt40s.
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Old 10-26-2012, 03:25 PM   #4
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What are y'all gapping your spark plugs at?
I gap mine at .045. I think it gives me a better spark and it's less strain on the ignition system to jump the spark over the narrower gap.
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Old 10-26-2012, 03:30 PM   #5
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I gap mine at .045. I think it gives me a better spark and it's less strain on the ignition system to jump the spark over the narrower gap.
You shouldn't have to worry about that until you add your s/c, especially with msd goodies.
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Old 10-26-2012, 04:31 PM   #6
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You shouldn't have to worry about that until you add your s/c, especially with msd goodies.
True most people wouldn't, I just checked the difference in the spark with a plug out and grounded on the engine. The spark kernel at .045" was brighter and fatter than the spark at .052", so that is the gap I use, plus the less gap the spark has to jump, the easier it is for your ignition to jump it.


With the SC & MSD ignition I will be gapping down even further probably around .035" to keep the fire lit under boost.
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Old 10-26-2012, 04:45 PM   #7
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True most people wouldn't, I just checked the difference in the spark with a plug out and grounded on the engine. The spark kernel at .045" was brighter and fatter than the spark at .052", so that is the gap I use, plus the less gap the spark has to jump, the easier it is for your ignition to jump it.

With the SC & MSD ignition I will be gapping down even further probably around .035" to keep the fire lit under boost.
Sweet. I may just try that test. It's funny because everyone always thinks that the larger the gap the better. But really it just strains the system. I run the .052 because that's what is recommended. But like I said I will try that test.
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Old 10-26-2012, 06:21 PM   #8
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Sweet. I may just try that test. It's funny because everyone always thinks that the larger the gap the better. But really it just strains the system. I run the .052 because that's what is recommended. But like I said I will try that test.
That's usually the case. The wider the gap, the more spark is exposed to the mixture, within reason of course. I did my experiment in the dark, and the tighter gap produced a better looking and more intense spark IMO. Try it sometime and see what you think. The only ignition add on I had at the time was a higher voltage coil.
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Old 10-26-2012, 08:39 PM   #9
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That's usually the case. The wider the gap, the more spark is exposed to the mixture, within reason of course. I did my experiment in the dark, and the tighter gap produced a better looking and more intense spark IMO. Try it sometime and see what you think. The only ignition add on I had at the time was a higher voltage coil.
yeah, thats the question. is it better to have a hair less spark thats more exposed? or is it better to have stronger spark thats less exposed? maybe i can do some testing with the wideband once i get everything dialed in perfectly. hmmmm......
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Old 10-26-2012, 09:19 PM   #10
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yeah, thats the question. is it better to have a hair less spark thats more exposed? or is it better to have stronger spark thats less exposed? maybe i can do some testing with the wideband once i get everything dialed in perfectly. hmmmm......
Let us know man! I've ran mine .01 wider than specs. I would love to know!
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Old 10-26-2012, 09:41 PM   #11
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Let us know man! I've ran mine .01 wider than specs. I would love to know!
it will be a while. i already parked her for the winter cause i killed my lifters. so not till the weather gets better.
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Old 10-26-2012, 10:22 PM   #12
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it will be a while. i already parked her for the winter cause i killed my lifters. so not till the weather gets better.
Gotcha man. I'm in Central TX where we don't worry bout that stuff!lol...
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Old 10-26-2012, 10:32 PM   #13
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Gotcha man. I'm in Central TX where we don't worry bout that stuff!lol...
whatevs!
i will probably do trojans test, with a small write up when she come back out of hybernation.. then log some a/f ratios. i currently havent been able to get my a/ f under 15.3:1, which is pretty darn lean. i have incresed the jets at least 4-6 sizes already. but i havent had any detonation and my plugs look great. which to me is strange because i am running serious timing. i dont know how im not pinging. my base timing is 16* with 21 * of advance! but it runs like a champ. i also have full msd setup including coil, box, and dizzy. so i should be making hella spark for the test.
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Old 10-27-2012, 04:16 AM   #14
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whatevs!
i will probably do trojans test, with a small write up when she come back out of hybernation.. then log some a/f ratios. i currently havent been able to get my a/ f under 15.3:1, which is pretty darn lean. i have incresed the jets at least 4-6 sizes already. but i havent had any detonation and my plugs look great. which to me is strange because i am running serious timing. i dont know how im not pinging. my base timing is 16* with 21 * of advance! but it runs like a champ. i also have full msd setup including coil, box, and dizzy. so i should be making hella spark for the test.
The spark I got at .045" like I said was brighter and fatter. (Everything I have read and researched has pretty much said that is what you want to ignite the mixture faster and more thoroughly. That and plug indexing to direct the spark kernel to the mixture ignition sweet spot.) Being brighter and more robust, it leads me to believe that it is hotter and will ignite the mixture better IMO. Maybe or maybe not, I've been wrong before and I'll likely be wrong again. Never know for sure unless you experiment.

If you really want to see a difference take a spare plug and work the ground strap electrode over like I outlined in the Useful Info thread.

I had a homemade spark plug tester in the shop, if I run across (can find) it and it still works I might be able to do the test and get some pics or vid of the spark. The only problem is that it may not be an entirely accurate comparison as I could only get about 15k to 20k volts out of it. Need to study up on how to "safely" increase the voltage to around 40k-45k like the MSD ignition. Then I could get some serious zappage.
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