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Old 07-05-2016, 05:26 PM   #1
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Spark plugs for boost

So I ran into an issue yesterday where one of my spark plugs was smacked shut somehow. I replaced all of my plugs with new Autolite 103's (same as what came out). The plugs that came out were gapped between 0.037"-0.041". I installed new plugs and gapped them to 0.032" thinking that the old ones were gapped a little wide, but now it seems like I'm not getting a full burn. If I go WOT my A/FR's start around 12.4 and then drop to 10.0 or less after reaching about 5k RPM's. Would that indicate my spark plug gap is too tight, or should I try to retune for the tighter gap?
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Old 07-05-2016, 05:42 PM   #2
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Forgot to add, I have a Vortech S-trim on 11psi and E-85
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Old 07-05-2016, 09:06 PM   #3
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I don't know much about tuning on E85, so this probably won't be much help.

You have the plugs setup like a typical boost application would require, so I don't see a problem there. And, doesn't the A/F ratio typically run richer when using E85?
At your altitude, I suppose that It is possible that you can get away with running a bit wider gap than at sea level.
It would be interesting to see if the A/F goes back up if you returned the spark plugs to the wider gap.
I assume that you didn't check the gaps before the dyno tune, so this would probably be a good question to ask your tuner... Whether a tighter gap is necessary, and if a new tune is required.

Are those Autolite 103's platinum tipped plugs?
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Old 07-05-2016, 09:30 PM   #4
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Originally Posted by straybullitt View Post
I don't know much about tuning on E85, so this probably won't be much help.

You have the plugs setup like a typical boost application would require, so I don't see a problem there. And, doesn't the A/F ratio typically run richer when using E85?
At your altitude, I suppose that It is possible that you can get away with running a bit wider gap than at sea level.
It would be interesting to see if the A/F goes back up if you returned the spark plugs to the wider gap.
I assume that you didn't check the gaps before the dyno tune, so this would probably be a good question to ask your tuner... Whether a tighter gap is necessary, and if a new tune is required.

Are those Autolite 103's platinum tipped plugs?
I might swap to pump gas and see if the same thing happens. My only thought is that the gap is just too tight for the amount of air going in and that the previous gap was correct.

No I did not check them before I went got my tune. My guess is he will recommend the gap I have set already. I don't know if they are platinum tipped, I just installed the same plug the previous owner had and didn't really pay attention
I'll look it up later.
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Old 07-06-2016, 11:36 AM   #5
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A non-resistor copper plug might work best with your application. But it doesn't seem like you are experiencing any spark blow out, so they probably aren't neccessary at this point.
And .032 gap is really just a general guideline. You actually want the gap as large as you can make it, without experiencing any spark blow out. So the .037-.041 gap could be acceptable to use with your setup.

Do you have another tune to use with pump gas?
How did the engine seem to react when it went rich? Was it down on power?
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Old 07-06-2016, 12:31 PM   #6
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I may swap them further down the road for something better. I brought home all the tools + a borescope to pull the plugs out so that will be my weekend project. I think I'll bump them to .037" and see what that does for me.

Yes I have a tune for 91 and a tune for E-85. All I gotta do is run the tank real low and load up on the other fuel.
It bogs bad, the first time it happened I thought traction control turned back on somehow. Once I was paying attention it would bog bad and run like **** until I lifted and let it idle for a few seconds. My guess is it just wasn't burning the fuel and started flooding the cylinders.
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Old 07-11-2016, 04:19 PM   #7
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Well I found out why my spark plug gap was so messed up..
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Old 07-11-2016, 04:31 PM   #8
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That'll do it.

So what's the plan?
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Old 07-11-2016, 04:41 PM   #9
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Haven't decided yet
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Old 06-25-2017, 11:09 PM   #10
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Any update on what kind of gap you ran that worked I'm in similar situation running gt40ps with s trim and 10 psi thinking of going with 103s and 35 gap

---------- Post added at 05:09 AM ---------- Previous post was at 05:08 AM ----------

What's that in the picture in scope I cant tell
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Old 06-25-2017, 11:20 PM   #11
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Any update on what kind of gap you ran that worked I'm in similar situation running gt40ps with s trim and 10 psi thinking of going with 103s and 35 gap

---------- Post added at 05:09 AM ---------- Previous post was at 05:08 AM ----------

What's that in the picture in scope I cant tell
I gapped mine to 32 and it seemed to work fine for me. The pictures is what was left of my piston in cylinder 7.
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Old 06-26-2017, 03:34 AM   #12
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Doesn't look like that spark plug gap worked very well...it did that damage?


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Old 06-26-2017, 03:40 AM   #13
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Doesn't look like that spark plug gap worked very well...it did that damage?


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No spark plug gap did not cause that. That was caused by too much timing on E85 and not enough fuel. The piston slowly disintegrated over time and kept knocking my spark plugs closed.
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