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Old 07-10-2005, 10:23 AM   #1
Amazake
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Default Plug Gapping with copper plugs

I use NGK BKR7E copper plugs.

I typically open up the box and toss them in.

What I found out recently was that they are not gapped to .030 as I have been under the assumption of. In a box of 10 all were gapped @ .036.

What is the effect of a wider gapped plug?


I change the copper plugs every oil change. So the effect long term is really irrelevent.
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Old 07-10-2005, 11:33 AM   #2
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Quote:
Originally Posted by Ngk Website
....Insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy..........Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add).
peace
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Old 07-10-2005, 04:25 PM   #3
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That is nice, but the car runs great with the .036 gap

Last edited by Amazake; 07-10-2005 at 07:19 PM.
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Old 07-10-2005, 07:20 PM   #4
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Why not use a wider gap if there is no misfire and no knock?

Aren't the benefits of a wider gap potenially added torque?
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Old 07-10-2005, 08:19 PM   #5
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I dunno. From what ngk says, it can result in less power and poor fuel economy. Having a bigger spark doesn't mean that the combustion will be any bigger.

peace
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Old 07-10-2005, 11:34 PM   #6
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.028 is the proper gap
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Old 07-11-2005, 12:16 AM   #7
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Wider gap tends to improve midrange torque a bit if you have enough ignition energy to drive the spark across the gap reliably. Large gaps are harder on ignition components (ie spark plug wires on cars that use them, and ignition coils break down sooner).

A wide gap forces the ignition coil to generate a higher energy spark (IF it CAN).

When the spark fires, your initial combustion forms a small kernal of flame about the same diameter as the spark gap. That small ball of flame grows very slowly at first ( the slow growth phase of combustion --- it is basically fighting for survival!). Then after a few microseconds it warms up the area surrounding the flame front and begins to be stretched out by turbulence in the chamber. If it is strong enough to stay lit, this is when combustion transitions to the fast burn phase.

A larger initial kernal, gives a bit better low and mid range torque (not much) and helps with low rpm off idle throttle response and emissions a bit as well.



Large gaps were popular in the late 1970's when the first high energy ignitions first came out that would support giant gaps -- some up to .050 - .080 gaps were used.

Just to grab some examples from a Chiltons manual

Ford mid 1974-76 spark plug gap .044 ( 0.60 calif)
Ford 1977-78 spark plug gap .044 ( 0.60 calif)

Chrysler all .035
Chevrolet 74 .035
----------75 .060
----------76-79 .045 or .035

Cadillac 75-70 .060
Buick 72-74 .040
------75-76 .060 (.080 260 cid 8 )
------77-79 .045 or .060

Pontiac 72-mid 73 .035
---------- mid 73-74 .040
---------- 75 -79 most .060 (403 cid .080)

You will notice a trend of increasing gaps then a drop in gaps. This was caused by problems due to maint on ignition break down over time and emissions problems when people did not keep up with recommended maint.

Obviously if you leave an .080 gap plug in the engine for 50,000 miles the gap gets REeeeAL BIG. Also it was determined that there is a diminishing return as gaps get larger than .040 -.050.

The NGK guidence of .004 / 50 hp is AFTER you find the best gap for your engine setup. I personally do not think the .028 gap many run is ideal except for those who run huge boost levels.

As a general rule run the widest gap you can that will give reliable ignition at high rpm and high boost.
This assumes your willing to replace plugs often enough to avoid missfire due to aging of the plug. I run a wider gap than most do !

Larry

Last edited by hotrod; 07-11-2005 at 10:58 AM.
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Old 07-11-2005, 04:00 AM   #8
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.028 is what Dyno Comp recommended for that plug on my dyno tuned ecutek vf39 setup. Runs just fine.
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Old 07-11-2005, 11:20 AM   #9
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Quote:
Originally Posted by Amazake
That is nice, but the car runs great with the .036 gap
But it runs better around 0.28
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Old 07-11-2005, 12:24 PM   #10
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Quote:
Originally Posted by cdvma
But it runs better around 0.28
Proof?
If he can make 5lbs more torque just from gapping the plugs bigger, why not?
The only problem is if the spark starts to "blow out"/missfire. I say gap them as big as you can witout going over ~.050" and without misfire at high load.
BTW Chris I think we gapped them to ~.038".

TMS
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Old 07-11-2005, 12:54 PM   #11
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no misfire, no blown coils, no problem.

imho
ken
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Old 07-11-2005, 03:50 PM   #12
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Quote:
Originally Posted by TheMadScientist
BTW Chris I think we gapped them to ~.038".

TMS
shhh! that was our little secret
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Old 07-11-2005, 04:10 PM   #13
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LOL
May be you should try bigger next oil change.

TMS
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Old 07-11-2005, 08:48 PM   #14
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Quote:
Originally Posted by TheMadScientist
Proof?
If he can make 5lbs more torque just from gapping the plugs bigger, why not?
The only problem is if the spark starts to "blow out"/missfire. I say gap them as big as you can witout going over ~.050" and without misfire at high load.
BTW Chris I think we gapped them to ~.038".

TMS
Like larry said, coils could die sooner. Why make your car the test dummy if you don't even know that you're getting more power? Is it worth having a higher chance of killing a $200 coil quicker(or four of them), misfire and preignition? I guess that's a question everyone has to answer for themselves, but I'm not gonna be running a gap of .040 anytime soon. Can someone post a link to an article that says bigger gaps make more power?

Quote:
Originally Posted by hotrod
....
The NGK guidence of .004 / 50 hp is AFTER you find the best gap for your engine setup. I personally do not think the .028 gap many run is ideal except for those who run huge boost levels.......

Larry
Are you saying that subaru shouldn't be trusted to know the right gap for their engines and electrical systems? When ya look at a tire and on the side it says "do not inflate over xpsi", do you inflate it with more then xpsi? Are you someone who ignores the little dots on the oil dipstick which tell ya how much oil to put in your engine? These questions aren't directed at larry, these are questions we should all ask ourselves. If your answer is no to both of those questions, why would you use a bigger gap then subaru recommends?

peace

Last edited by hippy; 07-11-2005 at 09:03 PM.
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Old 07-12-2005, 03:18 AM   #15
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Larry, you are so money and you don't even know it.

Did someone mention tighter gaps means quicker fouling. Subaru recommends 0.028" to 0.031" and I think they would know what their coil packs can handle long term. My rule of thumb is the widest gap that doesn't misfire. And the second one is never install plugs without checking the gap a couple of times--that whole measure twice cut once thing.

I've had considerable problems with misfires at precisely 5500-5600 RPM on my STI. I have adjusted fuel and spark timing to no end. Brand new plugs prevent the misfire, but then it will return once again after a few hundred miles. I have stock plugs gapped at 0.029. I haven't bothered to regap them because 1) its a pain in the butt to extract them, and 2) I've localized the problem to a specific boost condition that arises when I stomp on the pedal at over 4000 RPM, but under 5000 RPM. Pulling from 3000 is no problem. There's a little more boost spike then, and so really I think I need to solve the boost control issue first.

IMHO, colder plugs are a waste unless it's an all out race car that is operating under full boost most of the time. The plug temp rating is what's good for cruising. I wish Vishnu had never started the "colder plug" phenom'. I think it's totally bogus. I know of an STI running at 550+ whp on stock temp plugs and 900C EGTs with AFRs in the 12s. Tell a step colder makes any difference on 99% of our cars and I'll say prove it!! But, they will cause a lot of power robbing misfires.

Last edited by bboy; 07-12-2005 at 03:25 AM.
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Old 07-12-2005, 07:15 AM   #16
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Quote:
Originally Posted by hippy
Like larry said, coils could die sooner. Why make your car the test dummy if you don't even know that you're getting more power? Is it worth having a higher chance of killing a $200 coil quicker(or four of them), misfire and preignition? I guess that's a question everyone has to answer for themselves, but I'm not gonna be running a gap of .040 anytime soon. Can someone post a link to an article that says bigger gaps make more power?



Are you saying that subaru shouldn't be trusted to know the right gap for their engines and electrical systems? When ya look at a tire and on the side it says "do not inflate over xpsi", do you inflate it with more then xpsi? Are you someone who ignores the little dots on the oil dipstick which tell ya how much oil to put in your engine? These questions aren't directed at larry, these are questions we should all ask ourselves. If your answer is no to both of those questions, why would you use a bigger gap then subaru recommends?

peace

hippy, you make me laugh.

are you saying that subaru shouldn't be trusted to know the right:

swaybar diameter
tires
camber/caster suspension geometry
turbo
muffler
intercooler
injector size
ECM mapping
# of catalytic converters
gear ratios
paint thickness
etc... etc...

i could go on and on. how stock is YOUR car?

you see my point?
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Old 07-12-2005, 10:59 AM   #17
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I make a lot of people laugh, but I don't mind spouting...... So you have no proof that a bigger gap would make more power? I do see your point, but 99% of the things you listed have to do with cost, safety, ride quality, emissions, and/or longevity in mind. Changing the gap a little bigger probably wouldn't hurt ride quality, emissions, and definately wouldn't hurt cost. The only two things left(as far as I can tell) are longevity and safety. I do enough things to my car that hurting the longevity of parts or how safe they are any more just to test and see if a larger gap will make a tiny bit more power that I probably would never feel isn't top priority.

Time to babble a little more for your enjoyment. I run n2o every once in a while(maybe once or twice a week), and I've heard that running platinum plugs could cause problems with n2o. I've never actually tried it myself, and don't really understand how running platinum plugs would make a difference compared to other types of plugs(it's beyond me if they really make a difference), but I don't use them anyways. I beleive in the saying(this saying is gonna come back to me, I can feel it), "dumb people don't learn from their mistakes, smart people learn from their mistakes, and wise people learn from other peoples mistakes", and that's why I don't use platinum spark plugs with n2o. Not saying that they wouldn't work fine, but there're enough people who say that they cause problems that I don't need to test the theory(since other plugs are said to have no problems).

In the same way, when subaru says to run a .028-.031 gap, and ngk says to make the gap smaller with more power, I don't feel the need to test how big I can make the gap b4 the engine starts to misfire, preignite, or wear ignition parts quicker. There're people who test these things every day(like people at subaru and ngk), and maybe when there're enough people who put up some hard facts I will do it too. I'd rather be wise then smart though.

peace
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Old 07-12-2005, 11:08 AM   #18
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let's take your assertion to its logical extension:

why not make the gap tiny? let's go .010 or something.

why don't mfg's do this? with "cost, safety, ride quality, emissions, and/or longevity in mind"--the kernel won't blow out, no matter what boost and power, and your coil packs will have an easy time of it and will last forever. it doesn't cost anything more, and it's certainly not less safe. frankly i think they don't do it because it sucks.

if the larger kernel makes for a quicker propigation (and, thinking about it, i see no reason to believe it would NOT), then you COULD see a bit more torque. you're speeding up the CC characteristics. conversely, you could also just slightly retard the timing and enjoy a safer operating condition with a larger knock buffer.

the reason why nitrous and platinum don't like each other is because Pt is a catalyst.
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Old 07-12-2005, 11:15 AM   #19
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Would quicker propagation be like adding timing advance? Who says that having more retarded timing with quicker propagation would make a safer operating condition then just using the factory spec gap? Maybe subaru says to have a specific gap so it knows when to fire the plugs? Where's the proof?

peace
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Old 07-12-2005, 11:25 AM   #20
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hippy
You see Amazake is running his setup AT THE LIMIT. He holds the 3rd fastest 1/4 mile stock turbo WRX record on nasioc. He is doing every thing he can to make the car faster. Gapping the plugs bigger is just one of the many small things he is doing to try to optimize his setup. He is aware of the risks he is taking and is willing to accept the consequences if anything goes wrong. He is trying things that a lot of people don't feel is the right way to do things. But he is still one of the FASTEST stock turbo WRX's in the country. What he is doing WORKS and works well. Next I think he should index the plugs, again something that people feel is of no importance. But the people that feel that way are the people that run slower than him.

TMS
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Old 07-12-2005, 11:43 AM   #21
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There're many people who posten in this thread that know a lot more about cars then me, and I have no problem admitting it. You're talkin about someone who just found out he was using a larger gap then he thought he was using though(no offense amazake). It's not like he ment to use a bigger then stock gap to try and get a better time. Maybe if he used the stock gap(or even a little smaller) his times would be the same?

peace
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Old 07-31-2006, 02:38 PM   #22
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last plug change i gapped to 0.040. time before that was 0.035.

about 500 miles on the plugs, and no misfires yet. time will tell..
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Old 07-31-2006, 03:00 PM   #23
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Ohh nose not teh big gap.

TMS
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Old 07-31-2006, 03:19 PM   #24
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FWIW I don't have the luck you guys did. I think I have something else going on anyway...TGVs stuck which could be the big issue and not the plugs.
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Old 08-10-2006, 08:57 AM   #25
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Quote:
Originally Posted by ride5000
last plug change i gapped to 0.040. time before that was 0.035.

about 500 miles on the plugs, and no misfires yet. time will tell..
update: http://forums.nasioc.com/forums/show...1&postcount=10
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