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I know this get asked all of the time, and I tried the search...I'm getting continuous misfires after only a few months of installing new plugs. I want to put either TR6s or 103s in, but I'm not sure of the gap for either of them given my mods.

Thanks.
 

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Most gap between .055 and .057 inches. .050 to .060 isn't uncommon.
The wider the gap, the hotter and quicker the spark will be.
The shorter the gap creates a longer more sustained spark.
 

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But boosted, the higher the boost the narrower the gap must be or the higher the voltage/current (power) must be. So GM is confident that stock gap (0.060?) is good for the stock boost, but most people like a tad narrower (you know, we know more than GM! :) to have a larger buffer against boost or other related misfires.

Run as wide gap as you can get away with, big kernel gets more of the burn started at the time of the spark event, so a smaller one will take longer to get the burn started. Olds had 0.080" gaps on the HEI's for a few years in the 70's. Didn't last long.... hard as heck on coils.

"The slower the burn, the more time for things to go wrong...." some racer I can't recall who said it.....

Most gap between .055 and .057 inches. .050 to .060 isn't uncommon.
The wider the gap, the hotter and quicker the spark will be.
The shorter the gap creates a longer more sustained spark.
 

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I know this get asked all of the time, and I tried the search...I'm getting continuous misfires after only a few months of installing new plugs. I want to put either TR6s or 103s in, but I'm not sure of the gap for either of them given my mods.

Thanks.
103s are too cold for a 3.4 pulley setup... try some 104s if not siome 606s if your still fouling em out.. I'd try the 104's first at .057 ish gap...
 

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But boosted, the higher the boost the narrower the gap must be or the higher the voltage/current (power) must be. So GM is confident that stock gap (0.060?) is good for the stock boost, but most people like a tad narrower (you know, we know more than GM! :) to have a larger buffer against boost or other related misfires.

Run as wide gap as you can get away with, big kernel gets more of the burn started at the time of the spark event, so a smaller one will take longer to get the burn started. Olds had 0.080" gaps on the HEI's for a few years in the 70's. Didn't last long.... hard as heck on coils.

"The slower the burn, the more time for things to go wrong...." some racer I can't recall who said it.....
Yea, that pretty much nails it on the head. Run as wide a gap as possible without causing misfire or blow-out.
 

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I know this get asked all of the time, and I tried the search...I'm getting continuous misfires after only a few months of installing new plugs. I want to put either TR6s or 103s in, but I'm not sure of the gap for either of them given my mods.

Thanks.
Your set up isn't much different than mine. I'm running 104's gapped to .057.
I've back cut and rounded groundstrap edges with no problems now for at least 10K miles. Seems to have a "crisper" spark when back cut. These have to be replaced more often.
 

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I used to do that on my 455 Pontiac... I got around 12k on them on the stock HEI.

The older design of the Rapidfires had a good design, but not great plug life.

Your set up isn't much different than mine. I'm running 104's gapped to .057.
I've back cut and rounded groundstrap edges with no problems now for at least 10K miles. Seems to have a "crisper" spark when back cut. These have to be replaced more often.
 

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so then for my mods bin the sig. ur saying little bigger than .06 gap? (newbie question but hey thats how i learn)
 

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thats what i found out but the ford mechanic kept telling me to go higher. so i already hve them gaped my way
 

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Yup, I wouldn't go more than 0.060, I think mine are at 0.055 now with TR5's, they work fine. I might experiment with gaps this summer if I get "bored"....

You can set gap to say stock, then do a 100% repeatable acceleration run 3x (say 2nd gear, 40-60 mph or something like that, start lower and start stopwatch (datalogger best) at the 40 mph mark, and stop at 60, but do't stop accelerating till after the stopwatch stopped), then narrow gap say to 0.055, then run again, then repeat acceleration runs 3x. Find the median of the times. Is it faster/slower? If faster, then continue to narrow till it slows down. Conversely, if slower, go back to 0.060 and repeat to confirm baseline acceleration, then if confirmed, go to 0.065, if faster/slower, continue/retreat back and get closer to 0.060.

But be cautious on widening gap too far, it will make the coils run hotter, which can shorten lifespan of them. if racing, no biggie, if street driving, up to you....

Gaps make a diff, there is an RV shop that has done RV dyno work that has found around 18 hp on the 8100 Big Block Chevy by narrowing gap from 0.060 to 0.045. The theory is misfires at the higher rpm/loads were the culprit. Note that a 30k lb loaded RV in hot weather is quite a bit diff than a light weight GP with a boosted 231 in it.... But don't be surprised if you find some power with narrower gaps. Even my 454 (Vortec 7400, aka L29 454) picked up a fair bit of idle smoothness with a narrower gap. These were never the smoothest idling engines...

No, stay .060 or lower on your application.
 

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good point. illhave to have a little fun experimenting and ill see what happens, thanks
 

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That is a lot of the fun playing in this hobby, experimenting and seeing what works and what doesn't.

good point. illhave to have a little fun experimenting
and ill see what happens, thanks
 

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I think plug gap has as much to do with reliability as it does with performance. A car might run a really fast quarter at WOT with a particular gap but not be able to handle the variability of street driving. Those "low RPM - high load" situations are really hard on spark plugs. That's where they have a tendency to foul.
 

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But boosted, the higher the boost the narrower the gap must be or the higher the voltage/current (power) must be. So GM is confident that stock gap (0.060?) is good for the stock boost, but most people like a tad narrower (you know, we know more than GM! :) to have a larger buffer against boost or other related misfires.

Run as wide gap as you can get away with, big kernel gets more of the burn started at the time of the spark event, so a smaller one will take longer to get the burn started. Olds had 0.080" gaps on the HEI's for a few years in the 70's. Didn't last long.... hard as heck on coils.

"The slower the burn, the more time for things to go wrong...." some racer I can't recall who said it.....
Not sure why you are going so big with spark plug GAP..... I'm running a highly modded 3800 SC in a 2003 GTP and I have been doing a .035" gap for MANY years with ZERO problems. I use auto lite plugs(colder heat range 103's) . Guess I would suggest you make sure the plug wires are in top condition and the ignition coils are developing good spark(you can buy a spark tester pretty inexpensive and most auto part stores to confirm this). I hope some of this helps you out. Best of luck......Mr goodwrench
 

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I know this get asked all of the time, and I tried the search...I'm getting continuous misfires after only a few months of installing new plugs. I want to put either TR6s or 103s in, but I'm not sure of the gap for either of them given my mods.

Thanks.
That is strange you are having that problem with plugs. I have a HIGHLY MODDED GTP and have been using auto lite 103's for quite a while now with no issues. My first thought was is you engine running too lean or too rich.....either one of these conditions can cause spark plug issues. The only other thing I'm wondering about is if the coil pack is not putting out enough spark which would lead to plug fouling. Hope this helps. Mr Goodwrench
 

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Most gap between .055 and .057 inches. .050 to .060 isn't uncommon.
The wider the gap, the hotter and quicker the spark will be.
The shorter the gap creates a longer more sustained spark.
I was looking at my 2003 gtp owners manual(GM INFORMATION) AND found plug gaps were .060". Hope this helps. On another note, if the wires or plugs are not in good condition that might be part of you problem. I've been running the OEM info and have had no problems...... Best of luck......Jake (mr goodwrench)
 
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