LT1-LT4 Modifications 1993-97 Gen II Small Block V8

Plug gap - tr55s & msd

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Old Oct 21, 2012 | 01:08 AM
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Default Plug gap - tr55s & msd

Seeing a bunch of wierd **** around with guys saying they gap .30, .35? Saying the tighter the gap the stronger the spark... Isnt that completely wrong lol? Id say more like the tighter the gap the more consistent the spark... Bigger gap = more powerful burn as long as you can reach it right?


So stock is .50.. Ive got a full bolt on 97z28 with a MSD blaster coil, new GM opti, MSD 8.5mm wires, NGK tr55 plugs. I was thinking .55 for a little better performance all around with the more powerful coil, but could somebody set me straight on this? Just want the best overall performance, reliability, power, no missing, ya know.
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Old Oct 21, 2012 | 01:56 AM
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keep the stock gap, you have no reason to change anything and reinvent the wheel.


when your build calls for it, then change with edumacation
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Old Oct 21, 2012 | 02:06 AM
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For sure, im just trying to figure out why people are saying .35?

What about my 383 car.. I went stock gap, should it be diff? Forged le2 head 383 NA cc306 nothing fancy
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Old Oct 21, 2012 | 07:26 AM
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I agree with lt1slow..

For your 383, if it's something like a 12:1 CR motor, I'd gap at .040" as a starting point. If you have the desire and time to experiment, gap extra sets of plugs at .050" and at .060", take them to the track, watch your mph and listen for breakup on dragstrip passes to know when you've gone too far, then pick the midpoint, erring on the tight side. Keep in mind, that as they age, they won't tolerate as wide a gap.

I run a bone stock ignition, with .040" gap, 12:1 CR.
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Old Oct 21, 2012 | 07:41 AM
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The smaller gap is for longer duration ignitions. The larger gap is for shorter duration ignitions like a MSD 7AL 2/3.
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Old Oct 21, 2012 | 08:01 AM
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Originally Posted by Longbob
The smaller gap is for longer duration ignitions. The larger gap is for shorter duration ignitions like a MSD 7AL 2/3.
Good you mentioned that. Thus why I keep it tight with the stock (inductive) ignition.
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Old Oct 21, 2012 | 08:06 AM
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Originally Posted by bowtienut
Good you mentioned that. Thus why I keep it tight with the stock (inductive) ignition.

You are doing exactly what I would do. You mentioned modifying the gap and checking the results at the track. Another excellent idea.

My mention of the differences in ignition was to give someone an idea where and why you would want to start on the tight end or the wide end.
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Old Oct 22, 2012 | 10:15 AM
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Thanks for the tips i appreciate it, ive got an msd opti and coil.. Got a good deal otherwise inwould have just bought delco
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