I have TR55IX NGK'* in the car right now. I would like to drop down one or two heat ranges, has anyone tried thr TR 6, 7, or 8 IX plugs?
The TR8 might be to cold of a plug. I will probably just buy one plug and run it 500 miles then take it out and see what it looks like. Just wanted to see if anyone else has done this?

Well I am still running with those same plugs. I pulled them out a couple of weeks ago and they are fine with no carbon build up at all and the gap was unchanged.....not many miles on them though. I'll follow this post to see if anyone else has had trouble with going too cold.
Rogue has had no problems with colder standard type plugs these Iridium plugs are much too expensive to waste so soon.

I outgrew the TR55'*. They were only lasting about 3 or 4 months. I've got the TR6'* now, and after 6 months, they're doing fine. Had to replace one due to a bad wire and fouling, but the rest are still in fantastic condition.

The best plug that I have seen for the L67'* is the AC-Delco 41-919 plug. It is platinum so its lasts 100k+ miles, and it is 1.5 ranges colder than stock. It is a very good plug, perfect for the mods that most have, and it lasts forever. The only other plug i have seen that seems to be a better performing plug is the Autolite 103...however they seem to last about 500 miles in the GTP before it has a noticable loss in power...but it pulls like a mother unti the plugs wear out.

I couldn't really truthfully recommend anythign other than the 41-919'* for almost all people modding their L67'*...the GTP went 12.59 with them so its not like you can't go fast with them.

Shawn

I've got the double plantium Autolites, 2 range colder 103'* I believe and have no compliants, cars running great, will be checking them in 2 weeks when my new shinney TOG'* go in.