I am interested in the Iridium plugs, and first hand experience with them, particularly in race cars. I am currently running the NGKs at 20 psi on the road race course, but I'd like to see a longer performance window, one the Iridium should in theory offer. Also, there are three different"reaches" on the plugs in an 11 heat range, 19, 21, and 21.5 mm. I know from Mazda Comp, that they recomend a slimmer washer with the 6725, so I am thinking 21.5, but I'd like to hear from some users first. The car is making about 480rwhp on 110 octane on track, and I have not had a plug related starting problem/fouling with the 11.5s. Thanks, Carl

link to plugs, 34=11, 35=11.5 http://www.globaldenso.com/PLUG/cros...art/pn_01.html

 

Also, IIRC the HKS are denso, and if so they are "only" 28.95 a plug.

 

Let me know how they do. I have been using the NGK -115 plugs for about 8 years in my PP motors.