Plug gap on a supercharged Engine?

dcm0123

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What are you folks running for a plug gap on a Supercharged Engine?

Experiencing some drive-ability issues below 2K RPM.

Seen recommendations from .025 to .035"

94 Mustang, 5.8, Trick Flow heads, custom cam, Procharger, plugs Motorcraft 3923, coil MSD Ignition 8227, wires Motorcraft Performance M-12259-C301, Tweecer
 

white95

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I’m running .030, but I also have a 4.6 3V so that might not help.

What will help is suggesting trial and error. Record results and make a decision based on the data and what the plugs “tell you”.
 
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dcm0123

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Was running .035, picture of plugs below. What do you suggest I run?
Thank you
 

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TrickVert

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If your drivability problems are below 2K RPM and are, indeed, spark related, it's not because you're supercharged. Plug gap is reduced when spark blowout occurs at high RPM and is caused/exacerbated by the increased cylinder pressure from a FI system.

That said, suitable plug gap is inversely proportional to boost PSI and will also be determined by the ignition setup. I run a gap of .032 on mine with 10 PSI and a Crane ignition. Could I go wider? Probably, but it seems to be working so I don't mess with it.
 
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dcm0123

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After reading these responses I also have my doubts if it is the gap. Set it at .035 which is the previous setting.
Starting with new plugs, rotor, coil and cap to see where it gets me.
 
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dcm0123

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Some are darker than others. Not an expert but I do not think they are that bad considering the modifications to the engine.

Ran compression today and they are between 130 and 145 PSI.

What do folks running the factory emissions control system in a 94 or 95 with a Super Charger run for base timing?
 

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TTSaleen

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Some are darker than others. Not an expert but I do not think they are that bad considering the modifications to the engine.

Ran compression today and they are between 130 and 145 PSI.

What do folks running the factory emissions control system in a 94 or 95 with a Super Charger run for base timing?
Your plugs are really rich.
Have you had it dyno tuned and if so, what was the air/fuel ratio not only during the pull (wide open throttle) but at driveability/cruising? To me it appears to be on the rich side of things which causes the plugs to look like that. This can attribute to a strong odor of fuel from the exhaust and poor gas mileage in addition to a bucking at low rpms (due to unburnt fuel).
What is the fuel pressure? How does it run otherwise?
It may simply need the tune adjusted to be slightly leaner for the driveability.
Ryan
 
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dcm0123

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Its has never been on a Dyno.
It has a Tweecer but my son says if the battery goes dead, the tune is gone so he hesitates to put the effort into tuning it.
I will let you know the pressure this weekend. My recollections was around 40PSI at idle with vacuum line on.
 

lwarrior1016

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So, the battery going dead and losing the tune is a new one to me. I deal with tuned vehicles every day, and 90% of them end up with dead batteries.

The factory computer doesn’t erase its data when disconnected from the battery, and changing this tune is modifying the computers programming. It doesn’t just go away.
 

TTSaleen

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Its has never been on a Dyno.
It has a Tweecer but my son says if the battery goes dead, the tune is gone so he hesitates to put the effort into tuning it.
I will let you know the pressure this weekend. My recollections was around 40PSI at idle with vacuum line on.
OK. As others have also suggested, it would be wise to get a good dyno tune to see just what the car needs/wants for timing and air/fuel delivery.
To check the true fuel pressure, pull the vacuum line off (and plug the vacuum side with your finger) and with the car running see what the fuel pressure is reading. You should see this anywhere between 38-42 pounds without vacuum as a normal range. With vacuum reconnected it is completely normal for this to drop below that range. Give that a try and see if that at least helps lean it out some as I think it might be getting too much fuel pressure.
Also check the timing with a good timing light and ensure your marks are good to see. I have used white marking such as "white out" correction as something that stands out when using a timing light.
Set base timing with your spout connector removed and you need at least 10 degrees base timing, but with any mods I would go 12-14 range unless it starts to detonate then back it off a degree or so. Make sure to plug your spout connector back in!
Just these 2 things alone can make a huge difference on those cars!
Ryan
 

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