Spark plug gap

Al68

New Member
May 14, 2023
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Hello I’m new to the channel have a 68 ford Mustang coupe with a 94 ford gt engine that has aluminum heads and some more aftermarket upgrades don’t know much about it only that it sat for 9 yrs so I’m Changing all the fluids and spark plug notice the spark plug gap was 0.43 and I have new ones to install do I gap the new ones the same or gap at 0.52 engine also has efi snapper system. I’m a little nervous about changing out the plugs on a aluminum heads heard the horrible things that can go wrong help on gap setting
 
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I dunno what a 'snapper system' is. :shrug:

Gap the plugs to factory spec unless there's some specific reason not to. It doesn't pay to get too fancy with spark plugs.

Reasons to mess with the gap: Change in compression along with a tune, boost, nitrous...
 
If the ignition is stock and it's naturally aspirated, stick with the factory gap which is 0.052-0.056".

I don't know what EFI snapper system is? Is it a fish?
 
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If the OP has a Sniper setup theres a dropdown menu that you can choose the type of ignition and also the dwell can be modified to suit the spark output...

In all my years tuning and whatnot Ive learned alot from entities like MSD before MSD went chinese and melded with Holley...

Compression up to 10.25:1 gap can be safely between .050" - .060" wide...A wider gap creates a wider spark arc to fire the mix more intensely in the cylinder..

The compression of the engine dictates the initial sparkplug setting and therefore if a stock engine with GT40 heads runs about 8.5:1 compression you need to verify if your engine is making more or less compression than the stock engine because we all know that stock headgaskets are usually just .020" thick shims and the Felpro stuff starts out at .042" of thickness so its a matter of the preference of the engine as far as heatrange etc to fire the mix the most efficient way possible especially if the compression isnt up to par or higher than it previously was...

One thing for sure is with aluminum heads you want sparkplugs with a hotter heatrange or run the engine up over 200 degrees which I can see no benefit in doing as extra heat will expand metal parts even further.....

In my 410 w/ 10.25:1 comp and Edelbrock heads is it likes NGK V-groove racing plugs with .058" wide gaps and a 180 degree thermostat to make optimal power seeings I run a chip and dont run in closed loop ever because I dont want the ECU messing with my fuel trims......LOL

Best mod for any car with an EEC-IV ECU is adding a wideband controller into the EGR slot ..........

It makes a huge world of difference in the way the engine reacts and stays in tune with a wideband controller integrated in.....Even on a bone stock car!!
 
Last edited:
If the OP has a Sniper setup theres a dropdown menu that you can choose the type of ignition and also the dwell can be modified to suit the spark output...

In all my years tuning and whatnot Ive learned alot from entities like MSD before MSD went chinese and melded with Holley...

Compression up to 10.25:1 gap can be safely between .050" - .060" wide...A wider gap creates a wider spark arc to fire the mix more intensely in the cylinder..

The compression of the engine dictates the initial sparkplug setting and therefore if a stock engine with GT40 heads runs about 8.5:1 compression you need to verify if your engine is making more or less compression than the stock engine because we all know that stock headgaskets are usually just .020" thick shims and the Felpro stuff starts out at .042" of thickness so its a matter of the preference of the engine as far as heatrange etc to fire the mix the most efficient way possible especially if the compression isnt up to par or higher than it previously was...

One thing for sure is with aluminum heads you want sparkplugs with a hotter heatrange or run the engine up over 200 degrees which I can see no benefit in doing as extra heat will expand metal parts even further.....

In my 410 w/ 10.25:1 comp and Edelbrock heads is it likes NGK V-groove racing plugs with .058" wide gaps and a 180 degree thermostat to make optimal power seeings I run a chip and dont run in closed loop ever because I dont want the ECU messing with my fuel trims......LOL

Best mod for any car with an EEC-IV ECU is adding a wideband controller into the EGR slot ..........

It makes a huge world of difference in the way the engine reacts and stays in tune with a wideband controller integrated in.....Even on a bone stock car!!
Could you explain this?
 
I think what he's talking about is using the 5V reference for the EGR and repurposing it to a wideband signal converted to a 5V scale.

If so, some sort of tuning would still be necessary to interpret the repurposed 5V signal.

If my guess is even close and I were going to do something similar, I might just put a wideband on both sides, convert to a 5V reference, and let the EEC chew on that instead of data from the [switching on/off] narrowband sensor.