Ok, I'm sure this has been covered before but I couldn't find it on search :) besides, the info & preferences may be out of date now!

Just wondering what spark plugs people are using on the front and back rows, for the 3.0L and 3.5L (they use different plugs).

Also I am wondering what people think of the Bosch Platinum IR-Fusion, and of the NGK Iridium IX's. I just installed Iridium IX's in the front row, the back row is still the standard 100K Platinums. I have a 3.0L TF, the IR-Fusions aren't (officially) supported for it, but they do sound good!

So what do people think? 'best' plugs for front & back?

believe it or not, I've had someone (well respected) that used to work for Mitsu suggest just using standard plugs on front and back, just change them every 40000km is the best way to go, as you'd always have fresh plugs in that sense.

I've heard standard platinums aren't as good for spark intensity (aka oomph :)) as most people think. Its probably why you can mix them with the standard plugs in the front row since the spark intensity is probably the same as a standard plug. Um, except that I've mixed the normal platinums with the iridiums now... lol. Some that claim 100,000km are stretching things at that - I did a lot of googling when before I bought the Iridium IX's, even though they were my first choice for the front row anyway!

believe it or not, I've had someone (well respected) that used to work for Mitsu suggest just using standard plugs on front and back, just change them every 40000km is the best way to go, as you'd always have fresh plugs in that sense.
Good idea, provided you do the work yourself. Standard plugs should last that distance.

believe it or not, I've had someone (well respected) that used to work for Mitsu suggest just using standard plugs on front and back, just change them every 40000km is the best way to go, as you'd always have fresh plugs in that sense.

Standard copper core plugs will easily go that distance in a stock engine, even 50,000 is generally OK. Back when leaded fuel was used that wasn't possible.

If you want them to go big distance you need to set the gaps closer at 0.7-0.8mm (28-32 thou). Also if you can do it yourself file the gaps and reset gaps every 20-25k. I use closer gap on my iridiums too. A lot less load on the HT electrics and less risk of high rpm misfires and flashovers.

Cheers,
Alan

WHy waste time with conventional plugs? The huge advantage of platinum plugs is a genuine 80k km service interval.
Our TW used to get a slightly co**** idle after 20k kms on the plain plugs, throw in a set of Bosch platinums (6) for $30 and don't look back. I leave the plugs at the plug manufacturer's specified gap and have not had any ignition problems on anything I own (and I have them in one engine that sees 12k rpm daily), these are on my bike, they are NGK Iridium IX's.
No way known I would rely on any conventional plug for 50k kms, they just do not make that distance. I don't see the fun of pulling the intake manifold every 20k kms to change plugs, if you find it fun, go for it!
Platinum/iridium plugs were NOT designed to have more "spark intensity" they were developed to be self cleaning and long lasting. Iridium and platinum are both metals that handle very high temperatures, the reason these plugs have much finer electrodes is to allow these metals in the electrodes to run hotter so they reach their self cleaning temperature. Teh reason they can sometimes make more power is if they are used in engines that tend to foul plugs, whether it be running rich or whatever, they self clean up to a point.

Regards, Andrew.

Personally I do not like the Bosch, if I use the Patinum I use the NGK

As it is only 10 mins for me to pop my upper manifold off, I am using standard plugs at the moment with no issues at all. This is while I am playing with heat ranges as I am trying a little experement at the moment

Once I have settled where I want the range to be will most likely change over to platinum. When you look at it, I would normally change std plugs every 30k or so, that is about 3 sets of std which does work out slightly cheaper than platinums.

If you are paying labour to change then platinum is definately the way to go

I have the Bosch platinums front & rear - as said before, I think the only reason for the different plugs is the difficulty of changing the rear bank, so there's no technical difference in requirement. Been in for about 35k now & all's good. I guess it'll be interesting to see if there are any issues towards the end of their life; then again, the lump will be getting to 200k by then, so spark plugs may be the least of its problems...

Just as an aside, my wife's BA Falcon uses iridiums as standard, with a service interval of 150k - it's at 128k now, with no noticeable problems, & I haven't touched them at all.

WHy waste time with conventional plugs? The huge advantage of platinum plugs is a genuine 80k km service interval.
Our TW used to get a slightly co**** idle after 20k kms on the plain plugs, throw in a set of Bosch platinums (6) for $30 and don't look back. I leave the plugs at the plug manufacturer's specified gap and have not had any ignition problems on anything I own (and I have them in one engine that sees 12k rpm daily), these are on my bike, they are NGK Iridium IX's.
No way known I would rely on any conventional plug for 50k kms, they just do not make that distance. I don't see the fun of pulling the intake manifold every 20k kms to change plugs, if you find it fun, go for it!
Platinum/iridium plugs were NOT designed to have more "spark intensity" they were developed to be self cleaning and long lasting. Iridium and platinum are both metals that handle very high temperatures, the reason these plugs have much finer electrodes is to allow these metals in the electrodes to run hotter so they reach their self cleaning temperature. Teh reason they can sometimes make more power is if they are used in engines that tend to foul plugs, whether it be running rich or whatever, they self clean up to a point.

Regards, Andrew.

The reason the idle went off was the electrode gap got too wide and was eroded and oxidised. It was probably missing slightly under load too. Ideally copper plugs should be filed and gapped every 10,000km.

We are talking Magnas here not bikes. I can assure you they will last 50,000km on unleaded if the engine isn't using oil.

All plugs are self cleaning. If they aren't then the heat range is wrong or engine too rich/worn out rings etc. If you check the copper plugs in the front bank with the platinums in the rear you won't find any difference in plug cleanness.

The reason they have fine electrodes is because these metals are expensive and relatively erosion/oxidation proof so they don't need to be thick to maintain their gap width. The electrodes aren't thin to allow them to run higher temperatures. A high plug temp just leads to detonation or pre-ignition. All plugs are designed to operate at 500-750 deg C. Below 450 they won't self clean and above 800 they can begin to glow and pre-ignite.

Platinum and iridium plugs do not increase power. Some electrode styles can slightly affect combustion and power but that hasn't got anything to do with the material the electrodes are made of. In fact platinums can sometimes reduce power in engines that are high revving and with ignition systems having certain voltage rise characteristics. To help get around some of those issues iridiums were developed and if you can afford them silver electrodes are best.

Cheers,
Alan

The reason the idle went off was the electrode gap got too wide and was eroded and oxidised. It was probably missing slightly under load too. Ideally copper plugs should be filed and gapped every 10,000km.

We are talking Magnas here not bikes. I can assure you they will last 50,000km on unleaded if the engine isn't using oil.

All plugs are self cleaning. If they aren't then the heat range is wrong or engine too rich/worn out rings etc. If you check the copper plugs in the front bank with the platinums in the rear you won't find any difference in plug cleanness.

The reason they have fine electrodes is because these metals are expensive and relatively erosion/oxidation proof so they don't need to be thick to maintain their gap width. The electrodes aren't thin to allow them to run higher temperatures. A high plug temp just leads to detonation or pre-ignition. All plugs are designed to operate at 500-750 deg C. Below 450 they won't self clean and above 800 they can begin to glow and pre-ignite.

Platinum and iridium plugs do not increase power. Some electrode styles can slightly affect combustion and power but that hasn't got anything to do with the material the electrodes are made of. In fact platinums can sometimes reduce power in engines that are high revving and with ignition systems having certain voltage rise characteristics. To help get around some of those issues iridiums were developed and if you can afford them silver electrodes are best.

Cheers,
Alan

Spark plugs, they're like $2 each, and I don't enjoy pointlessly cleaning and regapping plugs. I gave up cleaning and gapping plugs after doing it about a dozen times on V8 engines, just too much work for too little reward.
The reason the electrdes are thinner (and I think we're saying the same thing, but from different angles) is that these metals can be much smaller in cross section and withstand the heat of their correct running temperature. Yes, there is also an advantage to using less of the rare earth metals due to price.
You'll have to forgive me, but in 20 years and over 20 different spark ignition vehicles, I have learnt to change plugs at a maximum of 20k kms. I know from experience it's really quite pointless to remove, gap, clean and replace plugs, when in one third the time I can replace the cheapest part of the ignition system and not worry about whether an insulator is going to crack or a ground electrode is going to fall off due to too many heat cycles etc.
I've also experienced first hand a couple of spark plugs that have had the insulators go porous and not fire under various conditions. So replacement is cheap and why all manufacturers recommend replacement rather than regapping.
I've never had a standard plug last more than 30k kms (with the correct gaps, fuel mitures, no engine oil control problems etc) and I personally feel replacement at 20k kms is just good, cheap insuance for reliability and low running costs. I also consider a big advantage of platinum/iridium plugs in aluminium alloy cylinder heads to be that you are only replacing the plugs say 3 or 4 times in the life of the engine, as opposed to 8 to 12 times for normal plugs or regapping. For me, that's 4 to 8 less opportunities for a cylinder head plug thread to get damaged and that makes it well worth while to me.

Regards, Andrew.

NKG Plugs are far superior to the the latest manufacture Bosch plugs.

The Champion RC10PYP4 plugs that were removed from my TJ (101,000Kilometers) rear bank this week would have been the original factory fitted ones.
I checked the gaps, and they were all a tight 1.1mm as specified. They were very clean and looked like they could have gone back in for another round.

Pablo

Spark plugs, they're like $2 each, and I don't enjoy pointlessly cleaning and regapping plugs. I gave up cleaning and gapping plugs after doing it about a dozen times on V8 engines, just too much work for too little reward.
The reason the electrdes are thinner (and I think we're saying the same thing, but from different angles) is that these metals can be much smaller in cross section and withstand the heat of their correct running temperature. Yes, there is also an advantage to using less of the rare earth metals due to price.
You'll have to forgive me, but in 20 years and over 20 different spark ignition vehicles, I have learnt to change plugs at a maximum of 20k kms. I know from experience it's really quite pointless to remove, gap, clean and replace plugs, when in one third the time I can replace the cheapest part of the ignition system and not worry about whether an insulator is going to crack or a ground electrode is going to fall off due to too many heat cycles etc.
I've also experienced first hand a couple of spark plugs that have had the insulators go porous and not fire under various conditions. So replacement is cheap and why all manufacturers recommend replacement rather than regapping.
I've never had a standard plug last more than 30k kms (with the correct gaps, fuel mitures, no engine oil control problems etc) and I personally feel replacement at 20k kms is just good, cheap insuance for reliability and low running costs. I also consider a big advantage of platinum/iridium plugs in aluminium alloy cylinder heads to be that you are only replacing the plugs say 3 or 4 times in the life of the engine, as opposed to 8 to 12 times for normal plugs or regapping. For me, that's 4 to 8 less opportunities for a cylinder head plug thread to get damaged and that makes it well worth while to me.

Regards, Andrew.

Sorry for late response. I've been away for a few weeks.

"Spark plugs, they're like $2 each, and I don't enjoy pointlessly cleaning and regapping plugs."

Andrew, I built my first engine 50 years ago and can't remember when I first did simple things like plugs. Spark plugs aren't $2 each and one of the reasons this planet is so full of rubbish and wasted resources is due to the throw away and no time to do simple everyday things attitude. Don't know how most today would survive changing the oil every 1,000 miles. Not to mention doing points, adjusting the timing etc. None of thats necessary now so doing plugs every 20,000 is no big problem and it gives you the chance to see how things like oil leaks, "flash ash" on plug connectors and distributor cap, water hose and vacuum hose condition are. And incidently most plug manufacturers are saying their standard copper core plugs have a service life of 30,000-40,000km. In America they say up to 45,000 miles. Mitsubishi USA specify 30,000miles/50,000km.

"The reason the electrdes are thinner ......... is that these metals can be much smaller in cross section and withstand the heat of their correct running temperature."

No the platinum/iridium electrodes are not thinner because they can withstand more heat. Conventional electrode plugs are available with thin center electrodes. These are mainly to suit race engines and 2 strokes. Conversely some plugs are made with very thick center electrodes too. These are OEM fitment mainly in the USA in petrol light trucks and pickups to allow longer intervals between plug service/changes.

Electrode thickness is determined by the need to maintain gap width for a certain number of ignition events. Each time a plug fires, electrons are expelled and metal lost, like a plasma stream, from the center electrode causing electrode erosion. In a conventional plug, gap width growth will be about 0.05-0.1mm in 10,000km. When a thin conventional material electrode is used the same erosion occurs but when its over a smaller surface area, due to the thinner electrode, the gap width increases rapidly. OK for 2 strokes that regularly foul the plug and need a service or for a race engine but no good for general road use. With platinum/iridium alloy center electrode the erosion and gap growth is very much less. In fact these alloys don't give up electrons very easily at all, so to increase spark intensity and get sufficent heat in the spark gap the electrode has to be thin. Electricity prefers to jump across hot sharp points and to get an acceptable intensity of spark and heat in the gap from a platinum/iridium electrode a thin pointy electrode is needed.

"I know from experience it's really quite pointless to remove, gap, clean and replace plugs"

You are correct. In fact just cleaning makes plugs worse. Plugs shouldn't need cleaning in a 4 stroke. Just see how much more voltage is needed to get a spark across the gap using a spark tester after a plug has been cleaned. What I said was "file and regap". Filing a conventional electrode removes the non-conductive "slag" from the electrode tips, exposes fresh virgin metal that conducts as good as new and produces sharp edges that electricity prefers to jump across. So if you haven't filed your plugs then that is why they haven't gone more than 30,000km.

"not worry about whether an insulator is going to crack or a ground electrode is going to fall off due to too many heat cycles etc."

If you have ground electrodes falling off and insulators cracking then you need to change plug brands or be more careful with selecting the correct heat range. Fitting platinums/iridiums should make this concern of yours worse as they have to cope with many more heat cycles and have the same insulator materials that go porous or crack just the same as ordinary plugs. And they have the same ground electrode material. Plugs called double platinum or double iridium have a tiny spot of precious metal welded on but the main body of the ground electrode is ordinary nickel steel. It is more usual for platinum to be welded on as iridium is notoriously difficult to reliably weld. In fact some manufacturers of supercharged and turbo engines do not fit iridium plugs and warn against their use due to the fragility of the electrodes. Thats also why plug makers say not to set the gap on platinums and iridiums, and if you do set the gaps there is no warranty on the plug.

"less opportunities for a cylinder head plug thread to get damaged and that makes it well worth while"

In my experience stripped threads are the result of incorrect fitting tension or a plug thread thats too long filling up with carbon, that then gouges the thread. Many also have no idea of how to correctly remove plugs. Whats required is to loosen 1/2 turn then retighten 1/2, loosen 3/4 turn and retighten 1/2 etc until the plug feels free. The back and foward action polishes the meshing of the threads and generally stops the plug thread "welding" onto the thread in the head and tearing it out. Race engines have plugs in and out all the time and seldom are theads stripped, even when done full hot, and they can be small 8mm and 10mm plugs that are much more prone to thread stripping. Actually I see more stripped threads when plugs are left in long term.

In an earlier post I mentioned using closer plug gaps than manufacturer settings. Here in Aust manufacturers are very concerned about idle quality, and our emissions standards and test cycle is not especially demanding, so big plug gaps are the norm. In countries where idle quality is not such an issue and where the emissions testing routine includes follow-up long term tests at the manufacturers normal service intervals, smaller plug gaps are usual to reduce the frequency of misfires. All engines misfire and misfire incidences increase with wider plug gap widths and the number of firing cycles experienced by the plug. Misfires reduce power, increases emissions and shorten CAT life so plug gaps are reduced to cut the misfires to an acceptable number. Big gaps produce a high intensity spark of short duration. A smaller gap results in a spark of much longer duration that is more likely to heat the fuel sufficiently to get a fire started and actually burning intensely enough that it will not be blown out by the intense swirling going on in the combustion chamber. Our 380 had 1.1mm gaps, but in other markets using the 3.8 engine Mitsubishi set the gap at 0.7-0.8mm with replacement at 7 yrs/105,000 miles/170,000km. And for the EVO IX its only 0.5-0.6mm.

The engineers at SAAB are quite some innovators and have come up with a lot of really good ideas for engines over the years. Just a pity they try to make cars. Anyway one engine they build has a variable spark gap. The spark plug has no ground/earth electrode. Instead the piston crown has a sharp point in the middle that the spark jumps across to. At cruise when engine volumetric is low and cylinder pressures are low the ECU adds a lot of spark advance so the plug fires perhaps 45 deg before the piston reaches TDC, so the spark gap is huge but thats OK as cylinder pressure is low and less pressure means the spark can jump further. Then when the engine is under load the ignition is retarded so the plug fires closer to TDC and the spark gap to the piston spike is smaller. So the engine effectively has wide gaps for better idle and narrow gaps for a stronger long duration spark and fewer misfires under load.

Cheers,
Alan

Alan, although I applaud your opinion on the "right way to do things" and reduce waste by reusing plugs after a bit of maintenance, most people these days simply do not have the time to be doing such a task.

my TW came from the factory with 6 iridiums.

Alan, although I applaud your opinion on the "right way to do things" and reduce waste by reusing plugs after a bit of maintenance, most people these days simply do not have the time to be doing such a task.

If you consider that the factory recommends replacing teh plugs (and they have a team of several hundred engineers plus tens of millions of kilometres of road and dyno testing) then right way is open to debate. It's easy to have spark plugs last forever and a day when all you do is plod along a highway. City driving demands replacement plugs due to more heavy fouling due mainly to many more cold start/run cycles and heat cycles.
The factory is concerned with many areas of performance, including reliability and economy of maintenance. Who wants to pay someone to spend a half hour filing and gapping plugs when you can forget about it for 80k kms?

Regards, Andrew.

In an earlier post I mentioned using closer plug gaps than manufacturer settings. Here in Aust manufacturers are very concerned about idle quality, and our emissions standards and test cycle is not especially demanding, so big plug gaps are the norm. In countries where idle quality is not such an issue and where the emissions testing routine includes follow-up long term tests at the manufacturers normal service intervals, smaller plug gaps are usual to reduce the frequency of misfires. All engines misfire and misfire incidences increase with wider plug gap widths and the number of firing cycles experienced by the plug. Misfires reduce power, increases emissions and shorten CAT life so plug gaps are reduced to cut the misfires to an acceptable number. Big gaps produce a high intensity spark of short duration. A smaller gap results in a spark of much longer duration that is more likely to heat the fuel sufficiently to get a fire started and actually burning intensely enough that it will not be blown out by the intense swirling going on in the combustion chamber. Our 380 had 1.1mm gaps, but in other markets using the 3.8 engine Mitsubishi set the gap at 0.7-0.8mm with replacement at 7 yrs/105,000 miles/170,000km. And for the EVO IX its only 0.5-0.6mm.

Cheers,
Alan

Alan. In my engine build with Grahams cams/springs and .0025 head skim for an approx 9.5 compressión ratio are you suggesting I would be OK or better to to use NGK Iridium Spark Plugs BKR6EIX with 0.8mm gap rather than the listed NGK Iridium BKR6EIX11 with 1.1 mm gap?

Cheers
Peter

guys this may sound like a stupid question, the tubing that goes down to the sparkplugs, that surrounds the copper, theres half missing on one of the plugs, will this make a difference at all?

guys this may sound like a stupid question, the tubing that goes down to the sparkplugs, that surrounds the copper, theres half missing on one of the plugs, will this make a difference at all?

Do you mean the spark plug boot (rubber tube) at the end of the spark plug lead or the spark plug itself?

Do you mean the spark plug boot (rubber tube) at the end of the spark plug lead or the spark plug itself?

the spark plug boot at the end of the leads...

yeah spark could arc to the wall, i would definitely replace that.

errr yeah get that replaced mate. maybe put some electrical tape around it until you can get it replaced.

Alan. In my engine build with Grahams cams/springs and .0025 head skim for an approx 9.5 compressión ratio are you suggesting I would be OK or better to to use NGK Iridium Spark Plugs BKR6EIX with 0.8mm gap rather than the listed NGK Iridium BKR6EIX11 with 1.1 mm gap?

Cheers
Peter

Yes I would definately recommend that. I run 0.8mm and if you checked with Graham I think you would find he might even run with a bit less than that. Just be very careful when regapping platinum/iridium. Its easy to damage the welded tips. Don't try sliding a feeler gauge into the gap as the sharp feeler strip edge can do damage too. A wire gauge is safer.

If you can afford 30 min every 12 months to file and regap them then you can use ordinary copper core plugs.

Cheers,
Alan

Yes I would definately recommend that. I run 0.8mm and if you checked with Graham I think you would find he might even run with a bit less than that. Just be very careful when regapping platinum/iridium. Its easy to damage the welded tips. Don't try sliding a feeler gauge into the gap as the sharp feeler strip edge can do damage too. A wire gauge is safer.

If you can afford 30 min every 12 months to file and regap them then you can use ordinary copper core plugs.

Cheers,
Alan

Thanks Alan,

I just picked up a Set of 6 NGK Iridium Spark Plugs BKR6EIX for $76 delivered so I wont have to regap them.

i just had a heart attack, i just got quoted 90 bucks for bosch leads and they dont sell them on there own as thats what i already have in my car. that was from rpw, as i went to my local auto shop, and they dont sell them :( any help be appreciated.

There was a bloke on eBay regularly selling them for $50 - Australian made for Mitsubishi. I bought some 6 months ago and he was relisting for ages after that. I'm at work and cant access my personal emails to check now but will do so tonight.

You could always go and grab a set from the wreckers - as its only the boot you need. Not sure if the boot easily detaches though.

Seller info
jib351

Starting bid: AU $55.00
Postage: AU $9.60Regular

Item number: 270472941831

Check Rockauto USA for Diamente/Magna parts. Aussie dollar pretty good at the moment. Platinum plugs are fairly cheap over there as well, just need to keep an eye on the delivery charge.
http://www.rockauto.com/