I am planning to get Denso IK-24 for my car. I will be around 310 whp and i was told that I need to get one step colder. If I get Denso IK-27. Someone told me that the exhaust will backfire with the IK-27's??

 

IK-24 is one step colder than stock, which would be IK-22.

PS. Denso IK-24s have been known to produce a high rpm miss after only a few months.. Quite a few F.I. owners have abandoned these in favour of copper racing plugs or just staying with OEM plugs.

 

Avoid the denso's. Also if you aren't very careful when gapping them you can damage the electrode and have it break off in your cylinder... = DOH

 

^ Freakin Denso. Get the NGK's and don't make a $4,000 mistake like how I did.

 

I got the NGK 7173's (one step colder). hope it is the right one. I also got a set of NGK 7405 (two step colder), who knows, maybe I will put some more boost in...

 

lol....so now all of a sudden you guys aren't telling everyone to go with Denso's instead of NGK's.

 

I don't think it was "all of a sudden". This happened over a period of several months to over a year as more and more F.I. owners discovered their engines would begin to miss and develop odd problems. I still don't have any reservations in using Denso Iridium plugs for NA applications on an S2000 or any other engine for that matter. I've had them in the wife's PT Cruiser for a couple of years now and it runs great.
I have never had any illusions about Denso Iridium plugs giving "amazing" gains in our cars. They just don't. But they should still give very long service life. Just not for F.I. use (in our cars).

 

I use NGK-R5671A-8. Burak, if you want to try them i have a bunch.

 

I'm running the Denso IK24s way beyond 310hp with no problem. I was running the IK27s but the 24s burn cleaner. The 22s also ran fine at high horsepower.
The pictures of the failed Densos I saw appeared to be caused by pre-ignition.

 

I run the IK27 also without any problem and maybe I should give the IK24 a try