I salesperson convinced me that the Denso Iridiums spark plugs would make my EVO run more efficient. Ha! Only if you leave it at stock boost.
I have a Profec BII boost controller set at 20 lbs to redline and the car would sputter like crazy. When I turned it down to 17lbs it would run fine. It was pissing me off.
However when I sprayed nitrous to the motor while running 20 lbs the sputtering stopped.
Which leads me to the conclusion that these so called high performance sparkplugs do not like the rich condition at high boost these EVOs put out. When I leaned it out with the NOS it ran fine.
I took those horrendous plugs back and luckily I kept the factory plugs and now my EVO is back to normal.
Hopefully there's no short or long term damage to the engine. Sometimes the factory dealer knows best.

 

I had been running the stock plugs for 18K mostly modified hard driving trouble free miles. I was planning to get a cooler heat range, but at the time I could not find anyone who had them in stock. I pulled the stock plugs, while the electrodes still looked like new (just one of the benefits of iridium) they had some fairly heavy deposits built up, so I cleaned them. Three hundred miles later they became fouled, which initially manifested itself as a miss/intermittent stumble at idle. I pulled and cleaned them again, (idle miss went away) this time they fouled out in less than 50 miles. I still could not get cooler plugs in yet and each time I cleaned the plugs the fouling just came back in short order, no matter how thoroughly I tried to clean the plugs . Since this is my daily driver I was forced to go buy a set of the over priced factory dealer plugs. Sure enough three days later I get a call saying that the cooler plugs came in, that figures.
Since I had a new set of stock plugs installed and a new set of cooler Denso plugs in hand, I figured this would be a good opportunity to do a little test. The Power FC I am using has a peak hold function that allows me to see the highest knock count that occurs during any period of time. Before switching to the cooler plugs I began bumping the timing and leaning the fuel mixture to the point that I would see significant knock on every WOT gear pull. I then installed the Denso IW24's (heat range 8) and went back out with the same tune settings. The consistent knock was pretty much completely gone! I am now able to safely run more aggressive fuel and timing, checking the plugs after 2K there is no sign of fouling and the engine seems to run smoother! I am now considering a set of heat range 9 plugs Denso IW27's.

BTW the Denso and HKS plugs are the same, I had them both in my hands, other than the lettering they are identical. The Denso's can be had for around $11 each, I think the HKS's run slightly higher. Here is some part number cross reference info:

(Stock) heat range 7 = Denso IW22, HKS S35G, NGK-iridium NA
Heat range 8 = Denso IW24, HKS S40G, NGK BR8 EIX
Heat range 9 = Denso IW27, HKS S45G, NGK BR9 EIX

The Denso/HKS plugs use a .4 MM center electrode with a U groove ground electrode. As opposed to the NGK, which have a .7 center electrode and no U groove, personally I like the Denso/HKS design better.

The Iridium vs cheap copper plug argument has been hashed through this forum several times. IMO there is just no contest, the Iridium plugs are far superior in every way. Ask any plug manufacturer and they will confirm this. Not to mention that you will end up replacing the copper plugs more frequently so the cost savings are really not there either.

This post is not to argue about copper vs iridium plugs, but to show that even mildly modified EVO's can significantly benefit with cooler plugs. I know this is not exactly new/ground-breaking information, but some have indicated that only a road race car might have significant benefits from cooler plugs. My little test indicated that this would be a great little mod for anyone.


__________________
A first grade teacher was reading the story of Chicken Little to her class. She came to the part where Chicken Little tried to warn the farmer. She read, ".... and so Chicken Little went to the farmer and said, "The sky is falling, the sky is falling!" She paused and asked the class, "And what do you think that farmer said?" One little boy raised his hand and said, "I think he said: Holy ****! A talking chicken!"


Last edited by SILVER SURFER on Nov 30, 2003 at 05:43 PM

 

Perhaps you got the wrong heat range with your new plugs. Lots of people have switched to densos and had no issues with the proper heat range for their application.

 

We are actually running the same NGK BPRES plugs in the EVO we have run in the DSM's for years. 5,6&7 heat ranges have all been tried for different things in the DSM's and now our EVO. The plugs perform flawlessly. We have them all instock and are $12 a set.
I will warn you all of one thing. Whatever you do, DO NOT RUN A PLATINUM PLUG in your engine. They run like crap, misfire and foul.

David Buschur
www.buschurracing.com

 

What is the correct gap for the EVO plugs?

 

bump

 

when should you change you plugs. At what mileage

 

is your car orange?

 

did you gap the plug before putting it in, or just installed it (sounds like a gapping issue to me).

We have used the copper NGK as well as the Iridiums for ages now on these motors, both perform flawlessly when gapped properly.

Ditto on the platinum thing.....great for mommies with BMW's who do 10k mile oil changes (since they last forever), but horrible conductors of electricity and awful in turbo applications.

As for when to change plugs, it depends. It's certainly easy to do on an Evo, takes maybe 20 minutes. If you just have the basic bolt ons at this point, I'd take a first look at around 10k miles just to make sure everything is working the way it should.

 

The installer gapped it to the same as the factory plug.

 

Maybe he damaged them also.

 

If he damaged them, why would they work fine only when I was spraying nitrous?

 

yea, I have denso 7 hrange, no issues at all.....

-Shahul

 

You never said what part number you had? Sounds like you probably had the wrong part or a defective plug? I have seen some people trying to sell the Denso IK20 for the EVO, those are correct for the earlier DSM cars but do not fit properly for the EVO. Somthing was obviously off in your situation, because the correct Denso plugs can and do work great in this car.
The Denso part number you should be using is IW22, IW24, or IW27. I am personally using the IW24, up to 23PSI with no problems.