plug questions for turbo
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 3,466
Likes: 43
From: Auburn MA
plug questions for turbo
I am building a rear-mount turbo setup for my 94 6 speed coupe and i am wondering what gap sized spark plugs to choose. I plan on running between 5 to 8 pounds of boost depending on the tune and i have always read that you need a cooler plug for forced induction however I never knew what that meant. Can someone help me pick the correct plugs
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Joined: Sep 2001
Posts: 14,674
Likes: 751
From: NEwhere Ohio
are these afr heads?
If so, call them.
My afr heads require a gasket plug, so i run autolite. I dont have the exact model .
Dont waste your money on expensive platinum or iridium plugs. Their tiny, cheap (smaller means less precious metal) electrodes can foul leaving you with a no start condition until you replace the plugs.
Also, there is a sweet spot with the gap.
on my supercharged 93, thats .035"
Any less and i will get misfires. More than that and i question if it will lite the spark under boost.
Also, if you are running optispark, you need a spark amplifier like an msd box.
Usually i hate msd, but have been having great luck with an msd 6btm (im not using the boost retard function, but its there in case i get bad gas, or cant find premium 93).
Good luck
If so, call them.
My afr heads require a gasket plug, so i run autolite. I dont have the exact model .
Dont waste your money on expensive platinum or iridium plugs. Their tiny, cheap (smaller means less precious metal) electrodes can foul leaving you with a no start condition until you replace the plugs.
Also, there is a sweet spot with the gap.
on my supercharged 93, thats .035"
Any less and i will get misfires. More than that and i question if it will lite the spark under boost.
Also, if you are running optispark, you need a spark amplifier like an msd box.
Usually i hate msd, but have been having great luck with an msd 6btm (im not using the boost retard function, but its there in case i get bad gas, or cant find premium 93).
Good luck
Drifting
Joined: May 2007
Posts: 1,426
Likes: 165
From: Motor City
You may have to change the gap. General rule of thumb is the largest gap size possible without misfires is where you want to be. The larger gap exposes more of the air/fuel mixture to the sparking area.
For heat range, usually every 75-100hp increase demands a one step colder plug. So, based on that decide how many steps colder you must go. I'd start your heat range selection on the cold side and work your way hotter by reading the plug (carbon fouled = go hotter). What you want to avoid is putting to hot of a plug in and having pre-ignition/detonation issues.
As far as material, I disagree with an earlier statement. Iridium is 6x harder and has a higher melting point than platinum. It may have a smaller volume of precious metal, but the materiel properties are better, making it last longer than platinum. Due to its material properties, a smaller size can be used on the center electrode which reduces the amount of voltage needed to ionize the gap. Another added benefit of iridium plugs with a smaller CE diameter is more area is given for the flame kernel to develop and propagate, which results in more efficient combustion.
For heat range, usually every 75-100hp increase demands a one step colder plug. So, based on that decide how many steps colder you must go. I'd start your heat range selection on the cold side and work your way hotter by reading the plug (carbon fouled = go hotter). What you want to avoid is putting to hot of a plug in and having pre-ignition/detonation issues.
As far as material, I disagree with an earlier statement. Iridium is 6x harder and has a higher melting point than platinum. It may have a smaller volume of precious metal, but the materiel properties are better, making it last longer than platinum. Due to its material properties, a smaller size can be used on the center electrode which reduces the amount of voltage needed to ionize the gap. Another added benefit of iridium plugs with a smaller CE diameter is more area is given for the flame kernel to develop and propagate, which results in more efficient combustion.
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Race Director
Joined: Sep 2001
Posts: 14,674
Likes: 751
From: NEwhere Ohio
You may have to change the gap. General rule of thumb is the largest gap size possible without misfires is where you want to be. The larger gap exposes more of the air/fuel mixture to the sparking area.
For heat range, usually every 75-100hp increase demands a one step colder plug. So, based on that decide how many steps colder you must go. I'd start your heat range selection on the cold side and work your way hotter by reading the plug (carbon fouled = go hotter). What you want to avoid is putting to hot of a plug in and having pre-ignition/detonation issues.
As far as material, I disagree with an earlier statement. Iridium is 6x harder and has a higher melting point than platinum. It may have a smaller volume of precious metal, but the materiel properties are better, making it last longer than platinum. Due to its material properties, a smaller size can be used on the center electrode which reduces the amount of voltage needed to ionize the gap. Another added benefit of iridium plugs with a smaller CE diameter is more area is given for the flame kernel to develop and propagate, which results in more efficient combustion.
For heat range, usually every 75-100hp increase demands a one step colder plug. So, based on that decide how many steps colder you must go. I'd start your heat range selection on the cold side and work your way hotter by reading the plug (carbon fouled = go hotter). What you want to avoid is putting to hot of a plug in and having pre-ignition/detonation issues.
As far as material, I disagree with an earlier statement. Iridium is 6x harder and has a higher melting point than platinum. It may have a smaller volume of precious metal, but the materiel properties are better, making it last longer than platinum. Due to its material properties, a smaller size can be used on the center electrode which reduces the amount of voltage needed to ionize the gap. Another added benefit of iridium plugs with a smaller CE diameter is more area is given for the flame kernel to develop and propagate, which results in more efficient combustion.
In my case gasket sealer must have damaged the o2 sensor
Drifting
Joined: May 2007
Posts: 1,426
Likes: 165
From: Motor City
Correct. If the mixture isn't dialed in, trying to spec a plug is like shooting darts in the dark. The plugs were not the cause of your fouling condition, but a victim of the environment.
Drifting
Joined: May 2007
Posts: 1,550
Likes: 324
From: Mid Ohio
If this is a new setup I'd go on the conservative side to start with. Use a standard plug, one range colder, cut the ground strap back to the center of the electrode, and gap at 0.025".
This will help to unshroud the kernal and ensure you get a solid spark while your trouble shooting other areas. Once the engine is running well and you have dialed in the A/F then.. play with plugs and gaps. (and wires)
btw, when I boost an engine I don't skimp on good wires and good plugs. Measure the resistance in the wires and get the kernal unshrounded (and index the plugs to boot)
This will help to unshroud the kernal and ensure you get a solid spark while your trouble shooting other areas. Once the engine is running well and you have dialed in the A/F then.. play with plugs and gaps. (and wires)
btw, when I boost an engine I don't skimp on good wires and good plugs. Measure the resistance in the wires and get the kernal unshrounded (and index the plugs to boot)