DrMerl

Question - did I ultimately help or hinder performance with the cooler Denso IW24 Iridium plug on a stock Evo?

I've been doing my reading over the months and I'm aware of reports saying that copper plugs sacrifice too much spark and you lose performance compaired to Iridium. Stay away from Platinum. Try out Denso (because HKS are the same with a different tip and more $, Denso's were $60). Some report that detonation events drop dramatically with one range cooler spark plug - IW24 (range 8) (equiv: HKS S40G, NGK BR8 EIX) as reported by an OBD-II logger.

I'm in San Diego and stuck with 91oct gas. I will not be running any other octane, and I will not use additives. I consistantly use Chevron. I have a K&N panel filter. I use the water sprayer (auto/man) at some point every time I drive and manually under accel when needed. I removed the stock plugs at approx 13,500 (looking pale whiteish, slightly tan, no carbon streaks on electrode, tip still with sharp edges) and put in the IW24s (did not change gap out of box) and now have about 700 miles on the new plugs. I did not reset the ECU and have let it relearn over the past few days.

I noticed that at 800-1200 rpm it became easier to get the car moving from a stop. I used to hear det sometimes in this range, right off idle with some load, and I'm thinking the ECU put back some timing in this area. Off boost response seems a little better at initial tip in.

Part throttle response (playing with open and closed loop accel and partial boost) has been improved enough to be noticable and improve fun factor. I'm down with how the butt dyno can be fooled with more or less hp and or torque, this feels like I got more advance type torque at part throttle.

Going to WOT and past 5500 felt "thicker" with slower RPM climb. I'm thinking that with the cooler plug the fuel is just drowning things out even more, and I lost HP. At 6000+ rpm with two passenger and going up hill at WOT my friend Clark (JWT) said he heard a touch of det still.

The powerband seems to be smoother overall. Thinking that I lose some up top, gain maybe in the midrange (more det prone here?), fewer det events occuring so the ECU can maintain more consistant timing?.

Car idles like normal and starts like normal

Has anyone else tried cooler plugs on a stock Evo running 91oct?
Have I only hurt performance or have I taken better advantage of 91oct and stock timing? Has anyone logged a before and after with this?

My overall impression right now is subtle and perhaps noticing the "loss" more up top, but sort of liking the improved rush in 4th or 5th at part throttle from 80-100. TIA.

DrMerl

More observations after driving are part throttle still seems great, but the sluggishness going to open loop or wot is even more accentuated. Going back to stock plugs soon.

boostedwrx

iTrader: (27)

It shouldnt ward off that much det. its just a small safeguard to draw a little more heat out of the cylnder head. I run the HKS S40G which is a grade 8, so one grade colder than stock. I cant tell the difference whatsoever with this plug or the stock plugs. I could, however, feel the difference with copper plugs with gappings from .024-.028. Car was more sluggish.

Check the gaps on your Iridiums. They should be .023-.024. The are gapped way closer than coppers. The should also come pregapped from the factory almost nuts on. The HKS ones (Denso) were anyway..