I have been fighting issues with my spark breaking up on my evo9 and it seems like its the plugs causing it. I am on my second set of IKH24s in a little less than a year.
I have lsx coils and just put new wires on last night and its a little better but its still breaking up when i get to about 24psi.
im on 93 and 4-5 degrees of timing above 5000 rpm.

i had denso cop coils on it for a while and it was doing ok at 32psi for a while but replaced them when the breaking up got really bad and the ls coils helped some but its still an issue. i am used to normal ngk stuff but this dumb evo 9 head takes special plugs and theres so few reasonable options.

ls coils are powered directly from the battery and grounded to the cam sensor housing and the head itself.

 

What's your current spark plug gap? The IKH24's are good plugs, but if you want them to function reliably under high boost they need to be gaped to .022" - .023" using a feeler gauge. I've run those plugs using .022" gap with 37 pounds of boost and a spoolin up cop with no spark blow out. This is with an engine burning oil heavily and covering the plugs in all kinds of crap.

To answer your question, they will last as long as the oem plugs, about 60,000 miles if your tune is good.

 

gap is about 022
i pulled them and they arent wet or oily, tune isnt as great as it could be but its not too far off.
I will try tightening the gap this afternoon i guess.

 

I've run these plugs for years without issues. Gapped at .018-.020 for 37-40lbs on a red with a denso cop.
I'd take a degree out there or lower the mivec in that area to lower cylinder pressure.

If the issue continues I would go over the ignition system and grounds.

Is it a large turbocharger ?

 

gap them to .020"

run ILFR7H plugs

 

Is NGK better than Denso 24s?

 

turbo is fp ss green. stock motor, s2 cams, ported head.

i will try those ngks next time i replace the plugs. Im hoping thats not the issue here if others are running them as long as they say.

 

How many miles are the plugs?

 

probably 6-8k

 

Replace with new NGK plugs. Eliminate a possible problem point. Gap them .020".


Even though they're iridium, plugs don't last long in boosted applications like ours. 28-30psi may not "seem" like much, but it is 100% racing engine territory for power level and cylinder pressures.

 

so the expected lifetime of these spark plugs is less than 10k?
I am going to try gapping them to 018 and see what happens first, but ill probably just replace them instead of chasing my tail.

 

Any time you add aftermarket coils, there is a chance of that being the issue, also. You could swap on the stock ones and see if there is any difference.

 

Any chance your ported head is flowing more or less air to that cylinder over the others on lower boosts where there aren't as big of a difference on high boosts? How does your plugs look?

 

If you drive the car hard, I would say not. I use iridium plugs in my car because coppers were barely making it 5-6k miles. I change the iridium plugs a couple times a year.

 

so i regapped the plugs to 018 and that fixed the issue.

when i was doing that i noticed the gaps were larger than im sure i originally set them to. i am pretty sure the little tiny electrode eroded away and opened up the gap. both times this issue has happened to me its grown gradually so it makes sense the gap slowly opened up over time.
so these plugs seem to require regular maintenance. Its no big deal for me to do, i just didnt realize i needed to.
ill regap them at oil changes for a while and see if thats the long term solution.