I have a 2001 SSEI. I have a Thrasher CAI, 3.4 Pulley, 180 Thermostat, 3 inch downpipe & coverter. Also have MSD coil packs. I have factory spark plugs now. Would like to change them. Should I stay with the stock ones or go one heat range colder. Also what brand should I use. Thank you

Go a range cooler, I been using autolite 104 with success, cheap too.
do a search there are many threads, on what people use, most stay away from bosch.
Heres a thread
http://www.bonnevilleclub.com/forum/...ic.php?t=57380

I'd run 2 heat ranges colder (I like the Autolight 104'*) and don't go below a 55 gap (you could prob. get away with stock gap).

I disagree. One heatrange colder is typical for a S2 with a 3.4 pulley.

I do agree, however, that with the hotter MSD'*, you can get away with a slightly larger gap.

INTENSE Racing, ZZP, W-Body Store all recommend Autolight 104'* for your app.

Directly from INTENSE'* website:
"Use Autolite® 104 spark plugs (two heat ranges colder than stock) if you have a 3800 Series II or III engine with 6 to 12 pounds of boost. At this level, we recommend reducing the spark plug gap to .050", or .035" with nitrous oxide."

While I agree with going colder, the factory heat range is run at 7.5-9lbs of boost stock. Not sure why ZZP is saying 2 ranges colder the 6-8lbs range that would normally occur in a stock application.

That quote is from INTENSE'* website.... In defence of Intense they don't say what that boost is from.... (turbo, MP112, CSC, Whipple, KB, etc.)

ZZP and W-Body Store don't go into as much detail and just say basically with the first bolt on mods 2 heat range colder plugs are recommended.

they put 104'* in mine.