Autolite 605 Iridium I believe is the one step colder that you should use.

 

I use the 605 Coppers for my supercharged

 

Since Keane is going to probably pay someone to do his plugs, I would recommend the Iridium just for the life of the plug.

 

Agreed, probably going to split things up half myself half someone else. Have to get a quote to see how bad its gonna hurt.

 

Found this information about plug heat ranges on 3800performances web site. I use Autolite 103's on my turbo app.

A general guideline for which spark plug heat range is right for your modified supercharged vehicle, are as followed:

- Use AutoLite 605's (one heat range colder) if your car is similarily modded like this: has a 3.40” supercharger pulley, CAI (cold air induction) setup, and a lower-temp thermostat.

- Use AutoLite 104's (two heat ranges colder) if your car is similarily modded like this: has a 3.25” supercharger pulley, 1.80:1 or 1.90:1 rocker arms or very mild cam, CAI setup, lower-temp thermostat, exhaust headers, cat-back exhaust system, and reprogrammed PCM.

- Use AutoLite 103's (three heat ranges colder) if your car is similarily modded like this: has a 3.0” supercharger pulley, 1.90:1 rocker arms or aggressive cam, CAI setup, lower-temp thermostat, exhaust headers, cat-back exhaust system, port and polished supercharger housing and/or throttle body, and reprogrammed PCM.

 

I'm kind of in the middle, as i'd like to change plugs and prepare for the future, and i'd like to do a plog, downpipe, tune, and maybe drop pulley sizes. So it's a mix between 605's or 104's i'd say.