Rocker 40h Anniv.

i have an 04 GT. I'm sure people have underdrive pulleys and was wondering if they make any noticable difference in their engine performance.

mac10chap

yeah, they make a decent difference on the 05s+. I would go ask someone in the New Edge section if they do good for on 04 though. I'm sure they do.

Nuke

They make about 4-8 RWHP on the S197 V8's from what I've read.

EDIT: They "FREE UP"..., not "make"

mrtstang

They do make a slight difference. It's not anything i could feel, but it made a difference when i raced my brothers 2006 Mustang gt. Before the udp's he would pull me ever so slightly in 3rd and 4th gear. Afterwards we were dead even everytime. We could start in 3rd, and were even until the top of 4th. So, they do seem to pull a little better on the high end.

mac10chap

all relative to the engine though. they could do better for 3V as opposed to 2V which is what the OP has.