I purchased my third evo a few months ago, and had the car tuned and have been racing it ever since. Put around 2500 hard miles and 3 autocross events with 12+ runs.

Recently, the car had been starting to make a "pop" every now and again but didn't get any knock counts. Ordered stock replacement plugs and went to install them, I found the below... keep in mind this is a IX, not a VIII.





I'm amazed that the car ran so well, and made over 350whp. Obviously it needs a retune now with the longer plugs, probably messed the timing up pretty good now that the car has normal plugs back in it.

 

LOL, previous owner fail! good find. now it will run even better.

 

Not sure you need a retune---the spark flame travel would be effected but not the timing.

 

I wouldn't think I would need to retune it either for plugs, but the TephraMod is on and is flashing fast (8+ counts) consistently over 5000rpm with the proper plugs in, so that's not good. Tried two sets of the plugs the ones in the pic IKH24 and the stock IL7RH gapped down to .020 and it's still there. The only knock before was once in a while on spool less than 3 count.

It does seem a bit leaner, though. Possibly getting a more complete burn and needs more fuel on top end, but I don't know a whole lot about tuning.

 

I would expect that returning the spark kernel from such a recessed location to the proper combustion area would give the effect of advancing the timing considerably. Basically, anything that impacts the development of the flame front will alter the piston position at which peak cylinder pressure occurs, which effectively changes the timing. Even so much as significantly changing spark plug gap can do this, and the difference between the wrong and correct plugs is far greater.

 

Thank you my friend, that makes a lot of sense.

I'm just glad I found this issue before running the car at Sebring for 2-3 hours in a couple of weeks.

 

I do maintenance on a friends 300C and found the same thing. I believe shady shops just use whatever they have in stock that will thread in and call it good.

 

Years ago a heard if install 9 plugs the Pistons will hit the plugs.
I guess not!

 

9 plugs in EVO 8 would hit the pistons, but this is EVO 9.

 

Lol I thought it was an 8

 

How much of a difference did it end up making?

 

seat of the pants feels like around 30hp and a lot smoother. But some timing does need to be pulled now, I pulled 3 deg across the board myself and knock stopped. The tuner is going to retune for half price and redyno it for me next Friday.