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Old 05-05-2003, 08:37 PM   #1
yebokmj
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Default Iridium spark plug DOHC vs SOHC Theory

I have this theory that they are problematic with the Subaru SOHC engines but not DOHC engines. I had them on my MY98 DOHC RS-T with no problems. I now have them on my MY97 SOHC L-T engine. With them on the SOHC engine I am constantly gettting miss fire code and I plan to pull them out this week for copper tops. I was told by others in the Aftermarket forum that Iridium plugs will cause misfire codes. But most people in the Aftermarket forum are running SOHC engines. People with WRXs don't seem to be having problems and I didn't have problems with my DOHC. Theh DOHC spark plugs come into the combustion chamber straight on unlike the SOHC ones that come on at an angle. Just a theory. Others thoughts?
Joshua
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Old 05-05-2003, 10:53 PM   #2
Eric SS
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Not sure. screwit and just get Copper NGK;s
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Old 05-06-2003, 12:04 AM   #3
HndaTch627
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are you regapping them?? if you are running boost thru a plug with a .044" gap you will blow the spark right out.

Jeremy
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Old 05-06-2003, 12:07 AM   #4
yebokmj
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Default Gap

I am running a .035 gap. I just pulled them a week ago and checked the gapping after once again getting a misfire code on two cyclinders. Maybe with Iridium I need to run a smaller gap? My current plan is just some NGK coppers unless I am told otherwise.
Joshua
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Old 05-06-2003, 06:53 PM   #5
wac
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Default Re: Iridium spark plug DOHC vs SOHC Theory

Quote:
Just a theory. Others thoughts?
Running the same ECU? Everything else the same?
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Old 05-06-2003, 08:43 PM   #6
yebokmj
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Default Everything is the same

Everything is the same, I am running the 2.2 ECU and new wires. I am assuming this is the problem but I will know for sure once I try changing the plugs to coppers. I am going to try this ideally tomorrow or thursday. I then am going home and therefore doing alot of driving so it will come on if it's not the plugs. It always comes on with in the first hundred miles or so.
Joshua
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Old 05-07-2003, 10:52 AM   #7
Z1 Performance
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Your theory is wrong - they work the same on DOHC cars as they do on SOHC cars - there is no difference in the number of ignition cycles for each head design.

What Iridium's are you using (brand and model number).

In all actuality, though we happily sell the Iridium's, I tend to prefer the NGK coppers above all.

Adam
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Old 05-07-2003, 11:28 AM   #8
Pavlo
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Depends on the boost, I have run them as tight as 0.020" gap (24psi boost on EJ20). Also oil getting in via breathers was fouling plugs at low rpm, causing misfire at high rpm.

Paul
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Old 05-07-2003, 11:42 AM   #9
yebokmj
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Default Brand

Well it was just a theory. Though I wasn't saying there was a differance in ignition cycles or anything I was talking about the way the spark plug enters the head. The spark plugs are Denso as to the part number I'm not sure since they are in the car, I am going to pull them today and put in some NGK coppers. I am running 8psi, possibly with the Iridium I need to run even a smaller gap than .035?
Joshua
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Old 05-09-2003, 07:56 AM   #10
subarurabbit
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I'm running a 0.040 gap on the legacy SS with NGK BKR6E-11 plugs and all is happy w/ 8.7 PSI.

That gap is per manual spec.
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