Does anybody use underdrive pulleys with their SC car. I haven't noticed any sigs mentioning this. I ask because I need a new serpentine belt and am thinking it may be something I would add on when I do my 11psi boost kit.

I have them on my car. I run 10.3 lb boost. I think they contribute along with a couple of other trinkets to the fact that I dyno 384 RWHP. I run the Evosport pullies, Will Turner told me they dynoed before and after on an E36 with their Dynopack and got a 12-13 RWHP difference.
Sounded good enough for me, so I put them on. Alternator pulley a PITA with the blower there. I had to take out the blower to get out the alternator to zing off the alternator pulley. The p/ s pulley and the water pump pulley are cake.
All these little mods really can add up in the RWHP of your car. I would not dismiss little changes because it all matters when you are looking for the EDGE over everyone elses car with similar mods.

I had them on before the SC install though...so...I can't really say if I would bother unless you are gonna be in there anyway. I suppose for the cost it is worth it though. Many say if you have a LTW fly already you don't notice the increase. If you don't have the LTW fly...it's an easy way to get the "revs quickly" feeling (as reported by others...I have both items)...

I have the lightweight flywheel going in and am jus thinking it may be worth doing all this work at the same time when I do the boost kit. I looked last night and can't figure out how that crank pulley is coming out of this car with the radiator in. It is very tight in there. PS I am waiting to hear from Nick G on software to put this kit together.

Bulldog also did you say your crank pulley is a six rib belt? Just want to make sure before I order the pulley from Vortech.

Why is the crank pulley coming out? Are you running the smaller 5.25 inch crank pulley and are increasing to the 6 inch one?And then what size Vortech blower pulley are you buying?

Correct I am going up to the 6" size and 3.33 Vortech pulley. I am still figuring out the cooling. I like the aquamist as this is mainly a street car that I take to track events 4 or 5 times a year. But am thinking long term I may want an intercooler.

Crank Pulley is a 6-rib. You CAN get the stock pulley out with the rad in place...BUT...you will not get the 6" blower pulley back in! ;)

BTW...I have been looking at the 8-rib possibilities...

Easily done...BUT...you would have to lose the Spal 16" electric fan...OR...use 2 small spals positioned to clear the pulley area. (at least on the MZ3) If there is room to pull the rad forward a bit (as Marco has done)...say a 1/4" even you might squeeze the whole shebang in as is!

Mine all barely fits with the 16 inch SPAL puller attached to a 58MM wide core PWR aluminum radiator. I can even slide a serpentine belt sideways between the crank pulley and the back of the fan.

You are still on a 6-rib..yes???

Yes, If I went 8 rib, the fan setup would definitely have to go.I have never slipped my blower belt, even on the dyno, run after run to 7000 RPM.