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.

 

Good stuff!

I appreciate your input. I have a set of the 8 heat range denso sitting in my garage. Picked them up from Z1 Perf for $48 shipped .

I finally got my SAFCII wired CORRECTLY this morning, so I'll switch to the Densos soon. I had the wrong pins, so I wasn't actually changing the fuel curve

I noticed some knock so I had to back off my fuel settings on my SAFC, so hopefully these other plugs offer a little more knock resistance.

Take care,

FB

 

Damn good stuff

 

always providing the good ****

 

Yea, Iridiums even feel better in my car. Been using the S40G's for about 10k miles.

 

Hmmm seems that there is something to the stock irridium plugs? Could they really just be a really heavy coating of irridium and not just irridium. Which method did you use to clean them up after every use?

 

Standard compressed air/pellet (basically a minni sand blaster) plug cleaner. It's not the electrode that caused the problem, it is deposits in the ceramic insulator that provide an alternate path for the spark. I cannot say if cleaning them necessarily caused a problem though.
They were fine until I stopped and got gas at this little hole in the wall station in the middle of no where Oklahoma. Almost immediately after that I started having problems. This is the first time I have had a plug were I just could not completely get rid of a deposit. But I have had other mechanics tell me that they have had similar problems. The general consensus was contaminated gas.
Maybe cleaning the plugs pitted the ceramic making it easier for deposits to become imbedded? I plan to avoid cleaning and reusing plugs in the future anyway.

 

Thanks for the good info. It's little nuggets like that that keep me checking this forum! Like the joke too

 

I always trust the surfers observations! Good write up, man!

 

Silver: If 7=IW20, then what it is IW=22?

because you claimed IW24=8


thanks,
Enrique

 

I had found a conversion chart off of a website, but after seeing your question I went to the Denso site http://www.iridiumpower.com/crossreference.php and started plugging in some standard NGK plugs to BP*ES values. I figured it must be a 7.5 heat range. But it turns out the IW22 is equivalent to a 7 (stock heat range) and the IW20 is a 6. The IW24 and IW27 were correct though. I edited the post already, thanks for the catch .
Denso does make in-between half heat ranges, equivalent to a 7.5, 8.5, etc. But their site says they are special heat ranges, which could mean they are hard to get.

 

Silver surfer.. great post!
do you have any pics of those old foulded plugs?

 

dumb question .. but did these plugs come pre gapped? i read somewhere that iridiums should not be gapped as the electrode can break?

 

You can actually see the carbon tracks on this one, this is with only about 50 miles since the last cleaning. With longer run times and heavier deposits it's usually not this easy to see the actual carbon tracks. Initially I was just getting a lot of missing/rough idle, after the fourth cleaning and the heavy tracking you see here, the engine would just fall on its face under high load, like hitting the rev limiter at 4-5K. I even went to my friends shop and let him take a crack at cleaning them with his plug cleaner.

The Denso plugs were pre-gaped at what appeared to be slightly less than .028 according to my feeler gauge. You can gap iridium plugs, you just need to use caution to not stress the fine center electrode. Since it is most efficient to run the largest gap that will fire under heavy load, and the Denso plugs have an even smaller electrode than the stock NGK plugs, I decided to increase the gap slightly at .030.

The following gaping procedure is from the Denso web site:

In most cases your Iridium Power plugs do not need to be gapped. Even with small variations in the factory set gap the ultra-efficient firing power design will compensate for those small variations. Should you decide to re-gap your Iridium Power plug, use extreme caution as improper gapping may damage or destroy the Iridium center electrode or porcelain center. To increase the gap size: Step 1 Use needle nose pliers or spark plug gapping tool to bend the ground strap up to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. To decrease the gap size: Step 1 Use the same method as above, however bend the ground strap down to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. WARNING: Failure to follow these directions may permanently damage the spark plug. Note: Never use a round gapping tool to check the gap or to increase or decrease the gap setting.

 

where would one get a "calibrated gapping tool" tried to find one when I installed my bpr7es's and just ended up using my good ol' round advanced auto gapper, it's chrome for that tool box "bling bling"