Since I'm messing around with ignition stuff, I decided to see if there was anything better than the stock Evo 9 NGK spark plug. When searching based on vehicle, the NGK website only shows the typical plugs for the Evo 9, so I searched based on thread dimensions and heat range. Here are the two candidates that I found. I purchased one of each so that I could assess the plugs.

NGK DILFR7B10G - This is very similar in appearance to the Evo 9 plug except that it has circular nub attached to the ground strap like the R35 GTR spark plug. The center electrode and ceramic insulator around the center electrode are identical in appearance to the stock Evo 9 ILFR7H plug. This plug comes gapped at 1.0 mm, so it would have to be gapped down slightly. The main concern for this plug is that after dropping the plug gap down to 0.8 mm, the ground strap still protrude 1.0 mm deeper into the combustion chamber than the stock Evo 9 ILFR7H plug. This seems like a pretty interesting plug to try except concern about the 1.0 mm extended ground.



NGK LFER7BHX - The electrode region of this plug looks quite a bit different than stock. The center electrode uses ruthenium rather than iridium, and it is 0.4 mm diameter rather than the usual 0.6 mm diameter. The insulator around the center electrode is noticeably thinner than the stock Evo 9 ILFR7H plug. Next, the ground strap has a thin platinum bar that sits over the center electrode. The ground strap does not extend over the center electrode - only the platinum bar. This plug comes with a 1.0 mm gap, and after dropping it down to 0.8 mm, the ground strap will also protrude 1.0 mm further into the combustion chamber. Overall, this plug seems too delicate for a high horsepower engine, but interestingly, its designated as a turbo/SC plug. I don't think I would try this plug.



So the question I have for people with knowledge of piston to spark plug ground strap clearance is whether a 1.0 mm further extended ground strap is going to be a problem.

 

Well, I ended up finding the answer pretty easily. I guess I should have searched first. I think that I'll try the DILFR7B10G.

https://www.evolutionm.net/forums/ev...ting-plug.html

 

If it's any help I just use the Denso plugs. Much cheaper and do the job.

 

Yeah, no issues with my ILFR7H plugs either, but I like evaluate different stuff once in a while.

 

I was never happy with those... car would often refuse to start if it was slightly rich..

 

While we’re on the topic of plugs and evo IXs, how long do you normally run your plugs for?

ive has my stock plugs in for 100k and haven’t had any issues (knock on wood). I know on my old evo 8 I was doing plugs wayyy more often.

 

10-15k miles.

 

Interesting. No obvious issues here with that, but maybe I don't know what I'm missing.