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Old 12-11-2003, 07:42 PM   #1
White2.5GT
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Default Cool info on spark plug gap

http://www.se-r.net/engine/platinum_copper_ngk.html

I found this while looking for info on spark plug gaps. I have a 1998 Legacy 2.5GT and changed the plugs from the plats that they come with stock to NGK coppers (BKR5E-11) Now I was wondering about the gap of the coppers should it be wider?should it be narrower?

According to this site when going from coppers to plats you should wider the gap. Does that mean when I switched from plats to copper I should have made the gap smaller?

I'm running them right now gapped at 0.041 in. The manuel calls for 0.039 to 0.043 in for the stock plats.
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Old 12-12-2003, 09:13 AM   #2
White2.5GT
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nobody has any clue about this stuff?
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Old 12-12-2003, 09:29 AM   #3
Legacy777
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AWD 6MT EJ22T AWIC Swap

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Run what your manual says.

I wouldn't put a whole lot of confidence in that page.
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Old 12-12-2003, 09:49 AM   #4
Warp3
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I'm not sure where they got that idea. For example, the 1999 Impreza owner's manual has multiple plugs listed (incl. both copper and platinum plugs) but only one gap spec range.

Shane -- http://www.warpthree.com
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Old 12-12-2003, 10:12 AM   #5
White2.5GT
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If you use a higher octane (burns slow) 89, 91 ect... would you benifit from increasing your gap a little? would it expose more flame to the mixture, and increase the burn efficency?
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Old 12-12-2003, 02:36 PM   #6
bongchild
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Default spark plug-related question....

Hey, anybody ever heard of indexing your spark plugs? Anyone ever tried it? Does it help? I read about it in HCI. Here's what it says: "Using a marker, mark the porcelain inline with the electrode. Screw the plug in the head and tighten. Make sure the mark aligns the way you want the opening of the electrode to face, favoring the intake valve."
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Old 12-12-2003, 04:39 PM   #7
NicEJ25
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sounds like too much hassle for not enough results. EJ engine have hemispheric combustion chamber, not those overhead valves head wich have some kind of squarry combustion chamber with egdes that induce detonation
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Old 12-12-2003, 09:30 PM   #8
Legacy777
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just gap the plugs to engine spec and stick them in......anything more and you're wasting your time.
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Old 12-13-2003, 02:41 AM   #9
DoorKnob
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Yay, I get to flex my nerd engineer skills again

I'm not sure where that guy in the link get's all his information from, and I wouldn't put a lot of faith in it.

First thing you want to know about fire is quenching. This happens when there are too many cold things around the flame that take away heat. When that happens your flame goes out because there isn't enough heat to ignite the surround mixture.

The second thing to know about flames, and probably more applicable to minimum spark plug gap is flame thickness. It's a little hard to explain (and understand), but the flame also needs to be a certain size before it can propagate. If you have a netting with holes below a certain size, the flame can't escape from it (these are called flame holders).

So that said, there is a minimum gap that is needed for a spark plug. If you make it too small, then you can't get a good flame going. Make it too big and you waste more energy trying to get the spark to jump across the gap.

Any other combustion engineers out there that can back me or poke holes in my arguement?
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