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Old 05-12-2005, 07:00 PM   #1
bboy
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Default Spark plugs- what's in your socket?

Common Spark Plugs Used By NASIOC Members

NGK IFLR6B (Iridium)--Subaru STI OEM Plug

NGK PLFR6-11 (Platinum)--used by a prominent tuner on his car

NGK LFR6AIX-11 (Iridium IX)
NGK LFR7AIX-11 (Iridium IX)--"one step colder"

Denso IKH20 (Iridium)
Denso IKH22 (Iridium)--"one step colder"

Denso supplies no information at all on the reach or gap of these plugs, none. No platinum was mentioned with respect to the IKH2x series of plugs, I'm assuming they are iriduim to steel.

Denso supplies the 2005 WRC Subaru team with a special plug. This plug has the iridium to platinum jump and has a more contained gap that is less likely to break, chip, dislodge, under hard racing condtions. Similar plugs made by Denso cost $35-40 per plug and are called "Denso Iridium Racing" plugs.

Common Plug Gaps Used By NASIOC Members

0.028-0.031 inches--from the STI factory manual (aka 0.7-0.8 mm)

0.028-0.029 inches--The "I gap'em 0.028-0.029 no matter what" school

0.044 inches--that's what the "-11" refers to at NGK -11= 1.1 mm = 0.044 inches

0.030-0.032--that's the real gap, even when the -11 means 0.044 inches

0.028 inches--"because itís a good compromise for power and longevity"

So What's What

NGK Iriduim vs. Iridium IX-- appears to be difference in the ground electrode. The plain Iridium plugs (a la OEM plugs) have platinum tip on the ground electrode and hence they cost more. The aftermarket "Iridium IX" lacks this platinum tip--it's steel. So, the OEM jumps/sparks from 0.7 mm Iriduim to a small platinum patch. The aftermarket jumps from a 0.7 mm Iridium tip to a steel ground, no platinum patch. (You might ask why iridium at all, why not copper or platinum--it's mainly becuase its a pain in the butt to change plugs and people won't pay for "tune-ups" ever 10,000 miles--iridium lasts longer)

NGK vs Denso--people don't like the Densos for one of three common reasons: 1) the smaller iridium patch (0.4 mm) fouls more easily than the NGK's 0.7 mm patch. 2) the Denso's are more fragile, you can easily knock the iridium off of the electro-tip, this fragile-ness may extend to detonation fragility as well, 3) they don't like the company, new comer to plugs, whatever.
__________________________________________________ _____

OK, why write this long winded post? Well, I'm misfiring, and a lot of other people are too. Now this is not coil-pack-gone-bad-style misfiring. I can detect mine at a very specific RPM range in 4th gear. Between 5-6000 RPM my car will cut-out ever so briefly maybe 3-4 times. It does not back fire and really makes no sound at all (no boom, no spark and vice versa), but you can feel the acceleration loss/re-engagement and there is a momentary loss of the boxer belch.

I could very well be misfiring in other gears, and at other RPM, but I just don't notice it.

When my car was on the dyno, Phil worked hard on tuning out a mis-fire at 5600 RPM. He tuned it out, but it's back, and in a few other spots nearby. I've tried to tune out the misfire myself, but nothing has worked.

What Plug/Gap to Use?

We'll I don't believe the "one step colder" stuff anymore (great for 2 stroke scooters though). It might make a difference if you car is solely a track car, but for most of us we are just fouling our plugs earlier because they are not running hot enough in normal "off-boost" driving.

I think most of the plugs above will work without misfires if they are gapped to do so. What the gap should be is a highly debatable factor.

I do believe that 0.044 is too large of a gap for a turbocharged engine.

I would stick to the stock "temperature range," which is 6, unless you have a damn good reason to run colder plugs that is proven to assist in your detonation problem--note the words: proven and problem.

I think Subaru is in the best position to determine the gap, and they recommend 0.028-0.031. The smaller the gap, the more guarantee that the plug will spark and not misfire (not spark). The plugs wear faster the smaller the gap, but plugs wear really fast if there's no spark.

Gapping an Iridium plug requires either a special tool or a great deal of care. Even checking the gap should be done with great care. The iridium tip is fragile no matter what manufacturer you buy. None the less, you should check the gap of the plugs you purchase before you install them, I in IMHO they should fall into the Subaru spec, and be matched to the same gap for all 4 plugs.
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Old 05-12-2005, 07:41 PM   #2
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Quote:
Originally Posted by bboy
Denso IKH20 (Iridium)
Denso IKH22 (Iridium)--"one step colder"

Denso supplies no information at all on the reach or gap of these plugs, none. No platinum was mentioned with respect to the IKH2x series of plugs, I'm assuming they are iriduim to steel.

.

From sparkplugs.com
IK20
Iridium plug, 14mm thread, 19mm reach, 16mm(5/8") hex, gasket seat, ISO height, 0.4mm iridium center electrode, tapered cut U-groove ground, resistor, 0.44" gap

IK22
Iridium plug, 14mm thread, 19mm reach, 16mm(5/8") hex, gasket seat, ISO height, 0.4mm iridium center electrode, tapered cut U-groove ground, resistor, 0.32" gap
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Old 05-12-2005, 07:44 PM   #3
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Quote:
Originally Posted by bboy
Gapping an Iridium plug requires either a special tool or a great deal of care. Even checking the gap should be done with great care.
Agreed.

A proper gapping tool is CHEAP and can prevent far more expensive problems in the long run.

When I gap a new set of plugs, I use a set of feeler gauges (also cheap) and a "go"/"no go" system to measure...
Example: If 0.031" doesn't fit, but 0.029" fits easily, then I'm at/near 0.030". No "forcing" is necessary, so the iridium tip doesn't take any stress at all.

Last edited by x99percent; 04-20-2007 at 12:21 PM.
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Old 05-12-2005, 07:47 PM   #4
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Quote:
Originally Posted by fastnoypi
From sparkplugs.com
IK20
Iridium plug, 14mm thread, 19mm reach, 16mm(5/8") hex, gasket seat, ISO height, 0.4mm iridium center electrode, tapered cut U-groove ground, resistor, 0.44" gap

IK22
Iridium plug, 14mm thread, 19mm reach, 16mm(5/8") hex, gasket seat, ISO height, 0.4mm iridium center electrode, tapered cut U-groove ground, resistor, 0.32" gap
Those are WRX plugs (note the missing "H" in the part number). Most of the information is correct, but the reach is *definitely* incorrect for the STi.
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Old 05-12-2005, 08:01 PM   #5
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Quote:
Originally Posted by x99percent
Those are WRX plugs (note the missing "H" in the part number). Most of the information is correct, but the reach is *definitely* incorrect for the STi.
My bad..looked too quick.

here are the correct ones:
IKH20
Iridium plug, 14mm thread, 26.5mm reach, 16mm(5/8") hex, gasket seat, ISO height, 0.4mm iridium center electrode, tapered cut U-groove ground, resistor, 0.44" gap

IKH22
Iridium plug, 14mm thread, 26.5mm reach, 16mm(5/8") hex, gasket seat, ISO height, 0.4mm iridium center electrode, tapered cut U-groove ground, resistor, 0.32" gap
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Old 05-12-2005, 08:22 PM   #6
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bboy, I think "our" problem is somewhat related to the Hydra. I haven't confirmed this yet, but misfires also happen to me 2. Remember that the Hydra can control almost everything about how the plugs operate.
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Old 05-12-2005, 08:22 PM   #7
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Great Post!! I think this one deserves a sticky.

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Old 05-12-2005, 08:27 PM   #8
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im looking at a box of ikh24s

crosseyed lol

chad b

good article
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Old 05-12-2005, 10:05 PM   #9
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Quote:
Originally Posted by x99percent
Those are WRX plugs (note the missing "H" in the part number). Most of the information is correct, but the reach is *definitely* incorrect for the STi.
He's correct. The STi reach is 26.5 mm, not 19 mm, the rest conforms to the STI's spec. Reach is one of those semi subjected items, but Subaru has selected 26.5 mm for all the new turbo models + the H6. It's not all about emissions and complete burning of the fuel, getting the spark in the middle can help power some.
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Old 05-12-2005, 10:23 PM   #10
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Quote:
Originally Posted by wgknestrick
bboy, I think "our" problem is somewhat related to the Hydra. I haven't confirmed this yet, but misfires also happen to me 2. Remember that the Hydra can control almost everything about how the plugs operate.
Well that may be another issue, but I don't think so, at least I don't have any evidence my Hydra is the issue.

I know of at least 4 cars here in Seattle (two with Hydras) and another "many STIs" that comes to me second hand. Some, but no means all of those cars are Hydra controlled cars.

I think the "meta" point of my post is that many of us STI owners, including me, need to be more careful about plug selection.

In my other combustion-centered hobby, I mod, tune, ride 2-stroke scooters. My Italjet has a 17:1 compression ratio, try that in a car. It's water cooled does 0-60 in 6 seconds and tops at 95 mph. But for me it's city transportation in a very congested city. I change my plugs about every 1-2 months rain or shine, and I read everyone of them. I can see the difference between Bardahl and Castrol oil. If I have a jetting problem, I know by reading the plugs. I run very cold plugs in the scooter, but operates at 9000 RPM all the time. My car doesn't.

I'm going back to the stock OEM plugs at the stock temp in my STi, and if I find that I have more detonation problems, I'll look into running colder plugs. I can tell you I really doubt this will occur, because at least one person is running 550 whp on stock temp plugs (daily driver, gapped to 0.028 in) no det, no misfire problems, and tuned with a Hydra--that would be Phil Grabow.

Keep that data point around when you think about running new plugs, especially colder ones.
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Old 05-12-2005, 11:50 PM   #11
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I'd give you an A for this article, IF it was posted in the right forum.
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Old 05-12-2005, 11:51 PM   #12
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I try to run as much gap as possible. You'll know when you have too much gap because of misfires. I am currently running .28 on my EVO after starting at .36 and reducing until the misfire is gone. My current plugs are the NGK copper 8s. They seem to run as well as the iridiums. I only picked them up after I broke a tip on the iridiums and needed something fast.
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Old 05-13-2005, 12:02 AM   #13
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XS engineering told me to run with apexi iso8's an I'm miss fireing on all four cylinders. They tell me it's the HKS BOV that is causing it because its 100% atmospheric... I would love for a real anwser to this.
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Old 05-13-2005, 12:19 AM   #14
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Quote:
Originally Posted by dragggn714
XS engineering told me to run with apexi iso8's an I'm miss fireing on all four cylinders. They tell me it's the HKS BOV that is causing it because its 100% atmospheric... I would love for a real anwser to this.
If that "8" is the same "8" heat range as NGK, those plugs are likely too cold for your application, unless your car is making crazy HP.
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Old 05-13-2005, 12:31 AM   #15
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ANY '-11' NGK plug is the WRONG plug for a turbo'd Subaru.

The gap is TOO BIG to be closed down far enough to make work and should be avoided......that is why they MAKE the NON '-11' plugs.

If the above is unclear to ANYONE....read this:


Q: What is the maximum I can open or close the gap?

A: NGK doesn't recommend adjusting the spark plug gap < or > .008". The reason for this is the ground electrode and center electrode won't line up properly, hindering spark plug performance.

http://www.ngksparkplugs.com/techinf...200&country=US
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Old 05-13-2005, 01:34 AM   #16
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I agree 0.044 is way to large a gap to jump for a boosted cylinder. However, some have stated that the -11 are not gapped 0.044, but rather 0.031-0.032 when you remove them from the box. Go figure. Nowhere have I seen a LFR6AIX-7 or -8, they are always -11, caveat preemptor.

I don't understand why this thread was moved. It's a 2.5L Turbo Engine Issue exclusively. And it's not maintenance we are talking about, people are using these alternative plugs for power enhancement (well to assist with power enhancement).
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Old 05-13-2005, 02:20 AM   #17
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...and no number is .7mm gap.....
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Old 05-18-2005, 08:31 PM   #18
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Well I put the stock plugs (NGK IFLR6B (Iridium)) back in. Out of the box they are gapped at 0.0285-0.030 inches, so there was some variation out of the box. I made the gap to 0.029 on all four. MISFIRES are GONE!!!!!

The plugs I took out were the NGK LFR7AIX-11 (Iridium IX). The gap on these was 0.030 pretty consistent. So the -11 was not 0.044 or 1.1 mm as the name would suggest. So the gap is closest to metric measure of 0.8 mm.

I confirmed that the difference between the Iridium and Iridium IX is the platinum tip on the ground electrode. In my opinion the OEM plugs are better plugs than the aftermarket "IX" designated plugs.

New plugs (the gap is slightly smaller too) cured my misfires, I'd recommend the change if you have bought into the "colder" plug mentality and you are having trouble with misfires, especially on the 2.5L Turbo engine.
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Old 05-19-2005, 01:42 AM   #19
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Quote:
Originally Posted by bboy
Well I put the stock plugs (NGK IFLR6B (Iridium)) back in. Out of the box they are gapped at 0.0285-0.030 inches, so there was some variation out of the box. I made the gap to 0.029 on all four. MISFIRES are GONE!!!!!

The plugs I took out were the NGK LFR7AIX-11 (Iridium IX). The gap on these was 0.030 pretty consistent. So the -11 was not 0.044 or 1.1 mm as the name would suggest. So the gap is closest to metric measure of 0.8 mm.

I confirmed that the difference between the Iridium and Iridium IX is the platinum tip on the ground electrode. In my opinion the OEM plugs are better plugs than the aftermarket "IX" designated plugs.

New plugs (the gap is slightly smaller too) cured my misfires, I'd recommend the change if you have bought into the "colder" plug mentality and you are having trouble with misfires, especially on the 2.5L Turbo engine.
...somebody gapped them before you got them, then....the manufacturers data has not been superseded or amended.
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Old 05-19-2005, 08:46 AM   #20
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Quote:
Originally Posted by bboy
Well I put the stock plugs (NGK IFLR6B (Iridium)) back in. Out of the box they are gapped at 0.0285-0.030 inches, so there was some variation out of the box. I made the gap to 0.029 on all four. MISFIRES are GONE!!!!!

The plugs I took out were the NGK LFR7AIX-11 (Iridium IX). The gap on these was 0.030 pretty consistent. So the -11 was not 0.044 or 1.1 mm as the name would suggest. So the gap is closest to metric measure of 0.8 mm.

I confirmed that the difference between the Iridium and Iridium IX is the platinum tip on the ground electrode. In my opinion the OEM plugs are better plugs than the aftermarket "IX" designated plugs.

New plugs (the gap is slightly smaller too) cured my misfires, I'd recommend the change if you have bought into the "colder" plug mentality and you are having trouble with misfires, especially on the 2.5L Turbo engine.
NGK part number LFR7AIX-11 is NOT the proper plug for the 2.5L Turbo motor... even if you were to attempt to properly gap them.

Direct from NGK:
Quote:
Originally Posted by Uncle Scotty
Q: What is the maximum I can open or close the gap?

A: NGK doesn't recommend adjusting the spark plug gap < or > .008". The reason for this is the ground electrode and center electrode won't line up properly, hindering spark plug performance.
I (and others) have been running NGK LFR7AIX plugs without issues.
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Old 06-27-2005, 03:55 PM   #21
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Well I'm confused, just got new NGK LFR6AIX-II stock no 6619 plugs, the gap is 0.41 or close to it. The NGK site recommeds this plug for the '05 STI but says the gap should be 0.030 or 0.032. Don't remember but to reset will be more than 0.008. They are new, return them? hwy61
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Old 06-27-2005, 04:49 PM   #22
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Return them. The NGK site is wrong.

Any NGK plug that ends in "-11" has a 1.1mm gap (~0.043"), which is too large for the WRX/STi/LGT/FXT. This should already be clear from all the information in this thread.
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Old 06-29-2005, 10:32 PM   #23
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I just swapped in some of the NGK V-power plugs and the car runs great. However, I still have a CEL for engine misfires despite the lack of noticeable misfires at any engine speed. I am quite confused.
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Old 06-29-2005, 11:34 PM   #24
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What does a good gapping tool look like? THe una FAQ isn't very clear on that, show me a picture!
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Old 06-30-2005, 12:29 AM   #25
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I like to use one that I got at Sears. It basically has 8 loops of wire of various thickness around the circumference of a circle. It looks like a circle with some loops of wire on it. I don't know how else to describe what it looks like. I would also suggest going to your local auto parts store and getting whatever their cheapest is; It is probably a circular tool but in this case it would have a ramp around the circumference that goes from 0.010 to maybe 0.065, with a scale attached, maybe 0.15 inches thick. These work really nicelly and the best part is the cost at about $1.99.
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