Just wondering if anyone has ever used asp underdrives and if you have did you feel a difference in power??
Is it a good or bad underdrive.

I also see that they make the ATI also,any input on that one would be greatly appreciated also but of course it is double the price of the asp.

 

I have this.
http://www.summitracing.com/parts/SUM-C2516/

Just like gears the under drive does not technically add HP it makes it easier to spin the belt system and spool up my rpm faster.
ATI is a very reputable brand.. .Summit is used by a lot of 3G's with positive results and is SFI approved. harmonic damper first and pulley second.
ASP maybe good now but they were pretty bad on 3G's a few years ago.

 

I think ASP had a problem with them awhile back, but it's been resolved and any of the newer pulley from them should be good. I've had one on my truck for like 15k miles and I think airram had one on his truck for nearly 100k with no issues.