There's a couple threads out there that did dyno's, semtex for one, as I recall.
5-6 whp is what you can expect, which is a very impressive cost to hp ratio.

I noticed the responsiveness more than any hp gains. Mind you, I was throwing on exhaust, intake, and h.f.c.'s all around the same time period, so it's kinda hard to recall each individual change.

hmm..i used these in the past..even expensive apexi ones..i really didnt notice anything at all..no power increase or response..

Thanks for the response on the UD Pulley Ztoon.

Just when I thought I was done adding parts looks like I'm going to have to get a Stillen UD Pulley soon.

The Stillen pulley weighs a fraction of the amount of the stock pulley. You wouldn't think it's much, but trust me, holding them both in your hand, you can tell there is a big difference.

Because of the lower weight, the engine revs a lot quicker. In other words, say that at 5000 RPM, you make X HP pre-pulley and (X+5) HP with the new pulley. That may not sound like much of a difference, but the thing is that you get to 5000 RPM in less time, so that (X+5) HP is available sooner.

How much was the pulley?