I have a set from Turner installed in conjuction with a Conforti Shark and CAI, along with a Supersprint exhaust. I can't separate out the effect of the pulley set, but I can say that I'm happy with the performance of my 2.5 Z3 and there seem to be no problems associated with the pulley reductions.
I run Eurosport UDPs and combined the mod with the fan delete mod. They work great and combined with the fan delete mod, I was able to cut my 1/4-mile drag time by nearly 0.3 seconds. Can't make any claims based strictly on the UDPs, but I'm quite pleased nonetheless.
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