What plugs to get

daivd z

Registered User
Ive been searching around and found that some people like the iridiums and some like the platnums. I was thinking about getting the Denso Iridium IT20's or the NGK TR55-IX's. Im going to be running about 15 psi with a FMIC. I want a colder plug than stock and one that is going to perform good. What would be the plug to go with?
 
I like the iridiums but I burned an NGK TR55-1IX back in March. I've replaced it and have had no more problems with the new plug but I did remove my chip module just in case and went back to the richer stock tune. I want to go back to the chip tune so I bought and just received a set of Denso IT22 iridiums to replace the NGK's. They are a "cool" plug where the IT20 is a 'medium' plug according to the list in the JEG's catalog. The TR55's have the extended tip as well as projected tip like the stock plug and sticks about 1/8" further into the combustion chamber than the Denso's do. I talked to NGK tech support today and asked why the extended tip. He basically said to put the spark in a little deeper to get better combustion and it burns a little hotter. The shorter plugs will run cooler by comparison and should do excellent in a moded motor. Justin at the Superchips Custom Tune that Jerry the tuner guy works for told me to use a F-150 Lightening plug, that the stock plug was too hot for my moded engine which is why I'm switching to IT22.
 
I run only standard copper plugs (Autolite 103's for a colder plug and 764's for everything else, gapped at .045). We do not run enough boost to need an Iridium plug to keep from blowing out a spark. At our boost levels a copper plug will perform better because it has less resistance. I replace mine about once every other year.

If you have a performance vehicle you should be replacing them anyway to make sure that you are getting maximum performance and to check for any combustion issues. It would be retarded to change out a $12 plug that often.

I have never seen a copper plug crap out on an SC even on Gary's Whipple powered SC at 23psi of boost and 440rwhp. My car never misses a beat and it runs faster than any other car with comperable mods.
 
After Dave was telling me about autolite 103 I got a set what a diffence over the stock ones no more ruff idle. :eek:
 
where can I get the autolite 103's at and what is the part number for them. the gap .045 for them?
 
Dave,

No way a copper plug has less resistence then an iridium being iridium conducts electricity bettery with less resistence..A quick glance on the Denso website

Denso Iridium spark plugs require on average 5,000 fewer volts to fire than conventional spark plugs.

If you drive your car I wouldnt reccomend copper plugs. They oxidise and break down quicker then platinum, or iridium eventually increasing the gap to the point where you get a miss. May not happen till 10,000 or 20,000miles (Maybe alot sooner with some problems thrown in)but it will happen.

You know how autolite platuinums generally fail? The copper under the platinum disk actually starts to oxidize and wear away. Hell if you have a front mount and can get yer plugs easy..Well ya could try copper...

Regardless after running very high boost for almost 30,000 miles my iridiums came out just fine...As a matter of fact they were reused in an unamed vehicle to this day..Working just fine....Without regapping..Afterall they specifically say do not regap:"O)...The platinums I had in thier wore out just as stated above...

Anyway the choice is yours

http://www.densoiridium.com/index.php?flash=1
 
DamonSlowpokeBaumann said:
Dave,

No way a copper plug has less resistence then an iridium being iridium conducts electricity bettery with less resistence..A quick glance on the Denso website

Denso Iridium spark plugs require on average 5,000 fewer volts to fire than conventional spark plugs.

I disagree. I feel the most likely the reason that Denso can claim that their plugs require less voltage to fire may have to do with the smaller gap you are directed to run.

The conductivity of copper: 595.8 1/mohm-cm
The conductivity of Iridium: 188.679 1/mohm-cm
The conductivity of Platinum: 94.34 1/mohm-cm

So copper has more than 3X the conductivity of Iridium and 6X the conductivity of platinum.

While iridium plugs may be capable of running for very long periods of time due to it's high melting point being beyond those encountered in a combustion chamber, I feel that running the same plugs in a performance car for that long of a time is counterproductive. You should pull the plugs yearly for inspection regardless as they are your "window" into the motor.

Not to mention that the plugs are still subject to other failures not related to the gap or electrode tips (cracked porcelins, fouling, etc).

:)
 
The conductivity of each of those metals is pretty irrelevent, especially since iridium plugs are an alloy of iridium and rhodium, not pure iridium, and the rest of the plug conductor is made of various different materials anyway. Plus the manner in which a high voltage AC signal travels through (or around, really) a conductor is different than one would intuitively think.

What IS relevent is the size of the electrode tip. The iridium tip is much smaller than platinum or copper plugs, and this alone results in lower voltage requirements for reliable spark. Or another way of looking at it would be you can reliably run a larger gap than otherwise with the same voltage. This is why the Iridium plugs come with a larger gap. The NGK TR55-IX plugs I got came with like a 0.060 - 0.062" gap! I had to adjust slightly for best performance.

BTW as far as the "do not gap" warning, I've been told this is because the smaller electrode is more easily broken than typical plugs, and they figure the average idiot will damage them trying to gap. However I think for us above-average idiots it's no problem, just be careful. Like all plugs, these are not gapped perfectly equal when you buy them, they need to be adjusted. You might adjust them to a larger gap than a typical plug (I set mine to around .056"), but you still need to do it.
 
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Rob but keep in mind that the larger the gap (without blowing the flame out) the more power you will make.

I was making 21psi (shuttup dave) with the Densos at the preset gap without a miss..Yes I was making to much boost but that is a testiment to how they work. Closing the gap besides leading to the potential of breaking the tip off might cause premature failure of the plug...I really dont know. I do know however that they were the best plugs I ever used on an SC to date as far as lasting.And with the larger gap they should be capable of making a tad more power...Anyone with a front mount willing to do before and after testing hehe
 
Well, anyway I use cheap plugs because they are that - cheap - and they work good. Although I came to the conclusion on my own that regular plugs are great for SC's on my own through my own testing, it is backed up by some very successful and well respected tuners and engine builders.

While there certainly isn't anything wrong with Denso's, I don't see the wisdom in spending $80 for plugs when most of the issues that cause damaged plugs are just as much an issue with a $12 plug vrs a $1 plug. I've not yet had an issue with blowing out spark, misfires, electrode erosion, etc. I did run the Denso's in my car for a time and didn't have any problems except that they became so fouled that they won't fire anymore. I still have them if anyone is interested...

I've also seen a number of instances where the entire electrode was blown completely off some NGK Iridium plugs (without nitrous or any other engine damage) which tells me again that the plugs are still vulnerable to the same issues which hurt standard plugs.

As to the ability of the Iridium plugs to fire under extreme boost conditions better than a standard plug - no issues here on that subject either. What I said in the beginning is that with the boost levels that we are seeing in our SC's cylinder pressure is not high enough to exceed the capabilities of a standard plug. I still feel that is true, and I would bet dollars to donuts that a brand new set of standard plugs will outperform a year old set of iridiums.

where can I get the autolite 103's at and what is the part number for them. the gap .045 for them?
Yes, that is the correct gap and 103 is the part number. ;) I get them at AZ.
 
My car runs the same no matter what plug or gap I put in it. I've tried standard tip Autolite dbl plats, short tip dbl plats and the long and short tip NGK iriduims. Gapped anywhere from .030 to stock....it just didn't matter. Right now I'm running NGK stock length and heat Iriduims re-gapped to .040.

My next plugs will be the cheap azz copper ones like Dave uses (that's what the turbo motor is getting).

David
 
the gap

So when I did my HGs, I put in Motorcraft double plats, gapped to .054. That what I was under the impression that the gap was to be set at. Is that too much gap for a stock motor and should I have gotten the cooper plugs Dave is talking about? I never knew plugs were so complex. Core, gap, tip, heatrange, it's just too much. :confused:


David
 
The Denso iridiums are copper plugs. They have a fine wire iridium tip instead of a standard nickel/iron tip. And $12 a plug isn't any worse than any of the other ridiculous go fast goodies I've bought for this car. :p
 
My car has recently had another nitrous backfire like it did last year a couple months before the shootout. Spark seems to be blowing out around 5700 rpm then Kaboom !! when the raw fuel and nitrous hits the headers and cats. Very similar to turning off the ignition and then back on to produce a backfire.

Last time this happened it clogged a cat, this time it sounds like it split the cat open. Anyhow I had NGK iriduims gapped to .040 in the car and it ran fine with nitrous several times at the track late last year and earlier this year. But it backfired both times I raced it the last time out. I think the boost was around 18 pounds and I was spraying a 100 HP nitrous nozzel and 75 HP fuel nozzel (same as used in Dayton a week earlier).

Other than a raspy exhaust note, it seems to be running fine after re-attaching boost gage hose and the fuel pressure vacuum line. Today I ordered a set of Denso IT20 Iriduims that I plan on re-gapping to .030 that I hope will prevent future blowouts when using the nitrous.

If that doesn't work, I guess I'll be upgrading the ignition system.

David
 
Well I know nothing but am currently learning and my input doesnt mean squat. I have had the motorcraft double platinums and they are crap. I bought the NGK TR55-IX and they are great. I had them gapped at 54 and they ran good. When my idle problem started I pulled them and regapped at 45 as Dave N stated in one of his posts. It ran much better. I personally think they burn better but what do i know. It was worth the $9 a piece.
 
Dahoopd said:
Well I know nothing but am currently learning and my input doesnt mean squat. I have had the motorcraft double platinums and they are crap. I bought the NGK TR55-IX and they are great. I had them gapped at 54 and they ran good. When my idle problem started I pulled them and regapped at 45 as Dave N stated in one of his posts. It ran much better. I personally think they burn better but what do i know. It was worth the $9 a piece.

I've had good luck with the NGKs too, but thought I would give the Densos a try this time. They are about twice the price of NGKs at a little over $12 a plug, so I hope they work twice as good :rolleyes: .

David
 
So should I take my autolites out and regap to .045? :confused: It runs good, but the idle is a little rough and sometimes drops low and the oil presure goes down and check gauge light comes on. If I slightly give it some give it some gas or put it in neutral, it recovers. Will regapping the plugs help this?
 
NCredSC said:
So should I take my autolites out and regap to .045? :confused: It runs good, but the idle is a little rough and sometimes drops low and the oil presure goes down and check gauge light comes on. If I slightly give it some give it some gas or put it in neutral, it recovers. Will regapping the plugs help this?

I would try resetting the idle before messing with the plugs. I use a tighter gap just to make sure I don't get spark blowout at high rpms and max boost. I don't think tightning the gap will do anything for the idle.

Because of the cam I've got, mine idles so ruff that I could be missing on two cylinders and not know it. If it smooths out when you give it the gas, the plugs should be okay.

David
 
David Neibert said:
I would try resetting the idle before messing with the plugs. I use a tighter gap just to make sure I don't get spark blowout at high rpms and max boost. I don't think tightning the gap will do anything for the idle.

Because of the cam I've got, mine idles so ruff that I could be missing on two cylinders and not know it. If it smooths out when you give it the gas, the plugs should be okay.

David

It idles good most of the time, but sometimes it drops a little lower and cause the issues I stated above. It's an intermitant thing. Usually though, it happens after the car is warmed up good.
 
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