Platinium plugs can create a hot spot to cause detonation in turboed cars. This is in spite of whatever heat range you choose.

Iridium ones are fine, so I don't know the reason why they aren't recommended. I do know that they are expensive though.

 

Platinum isn't as good a conductor of electricity as copper is. Platinum plugs simply don't fire worth a damn in a high pressure engine like ours.

Platinum is added to the ends of the electrodes simply for longevity. But they actually perform worse than a normal copper plug.

 

The stock plugs for the Evo are NGK IGR7A-G. According to the Evo repair manual, at least.

They are iridium plugs with a platinum ground electrode.

This doesn't mean that a copper plug won't work just as well. But a copper plug definitely won't last as long. I change my plugs at least twice a year.

 

Josh,

Where have you seen the EVO repair manual?

 

Platinums suck...hehe, no. Platinums run hot, really hot and you don't want that hotness in a forced induction car that's already running hot. Platnium doesn't conduct electrcity that well either, Iridiums run basically like platniums, waste of money, they run hot and they don't do a good job at sparking.

 

Dude - Iridiums are NOT like platimums. Iridiums are easier to fire than any other plug. Under the same conditions the Iridiums require 5,000-10,000 less volts than any other plug. This means that they can fire in higher cylinder pressures at the same voltage than other plugs, or fire across a larger gap. Please explain how this means 'they don't do a good job at sparking'. Usually both of these items are considered "a good thing". Especially considering it is scientificly proven, as well as proven on a Dyno (real world testing).

Where is your (dis)information coming from?

 

okay so Denso Iridium or Copper NGK.... it didnt seem like either side came to any conclusions....
both came up with good points....

-Shahul

 

Replacing the plugs with Copper NGKs costs $10. It takes 10 minutes. So why not try them out?

If you have already worn out the Iridiums, then I'd definitely get the coppers. Who wants to spend that much money on spark plugs every 3 months?

 

what is the gap, is it .028?

-Shahul

 

The spark plug gap is shown as 0.028 to 0.031 in the service manual.

I always use 0.028.

 

don't want to add fuel to fire.. but hope the former/current DSM owners DON'T compare their engines to the evo's .. they are DIFFERENT even though they share the same code.. Standard VII/VIII comes with iridiums, the twin coil wasted sparks generate ALOT less energy than you would believe (if you don't believe me, gap your plugs at 0.9mm vs the recommended 0.8mm or less)..

You really can use the cheaper plugs .. you lose power plenty fast too.. then again .. if you look at the service manual .. the stock plugs last longer than the standard copper plugs in the normal cars .. comparative

Anyway .. there's another type of plug which you can consider .. its the wire style plugs .. ralliart/hks/denso all makes it .. and they are expensive .. but there's a US made plugs which I think it's called turboplugs and these go for $40 a set ..

 

so what model Denso Iridium plug are we talking here for a cooler spark?

-Shahul

 

Umm...the engines are virtually identical. The pistons are a couple points higher in compression 8.8:1 compared to my 8.5:1. The head has smaller ports. The intake manifold has shorter runners.

The twin wasted spark ignition on a DSM works just fine at 27psi of boost, generating over 500hp with copper spark plugs at 0.028" gap.

So the Evo's coils suck, but the DSM coils rule? I find that hard to belive since the Evo just about has a coil on plug setup.

 

the heat range of the plug determines how "hot" or "cold" they run (which refers to how quickly they extract heat from the combustion chamber.

Iridium plugs work well as they are good conductor of electricity, yet are very hard, so they ofer a good service life even at high bosot levels. We use them for the WRX's alot, as the copper ones in 1 step "colder" are nearly impossible to find..I can look up the Denso Iridiums for the Evo tomorrow and post here if you guys want. A big benfit many cite with the iridiums is they can be gapped wider 9more efficient spark) yet still fire at a solid level.

Any coil on plug setup is good.....they are about the highest capacity ignition units you can get, and should be able to fire well to at least 8500 rpm or so (estimation only..someone like Shiv would know better though).

At the end of the day, if you ask 10 people this question, you'll get 20 answers, so do the research, learn teh facts, speak to people who run various combos, and then buy accodrdingly.

happy boosting

 

,

NGK coppers with a heat range lower, Vishnu sell them on there site.

Eric