I have the Vishnu Power Pulley. I had it installed as part of a kit so I can't say that you would feel the difference as measured on the ol' butt dyno. I would say that it's probably worth what Vishnu claims for HP gains, since they tend not to include or sell many popular items like cold-air intakes, blow-off valves, and front-mount intercoolers because they don't believe these devices offer a good value of HP to the dollar.

I've lived with the pulley through a hot summer of 90+ degree weather and haven't noticed any difference in air-conditioning output, nor do the lights go any dimmer at idle than before the pulley change.

--
0==WW==0
"…axles of evil…" - george w. bush

 

I've had a Unorthodox Power Pulley (Underdriven and lightened) in my car for about 2 years now (about 8 months with VS2). Makes my car feel lighter when stepping on the gas when it's not in gear. Just blip the gas with a stock pulley-car and notice how long it takes for the RPM needle to climb, then do the same thing on a car with a pulley installed, then you'll notice the difference.

tk

 

I also have the Vishnu UD pulley. I put mine in with my UPpipe, so I couldn't tell you the difference. However there is one thing for you to be aware of:

When I got my Cobb Stage 2 reflash, I asked if they had any specific maps for the crank pulley. They guy there (don't remember who it was) told me that they didn't recommend using the crank pulley because it could throw off your crank position sensor. I did a little digging, and this HAS been known to happen. Most of the time it is in conjunction with a lightenend flywheel.

I have had NO problems with mine. IT works great, and I have minimal dimming of headlights at idle. I would recommend it due to losing 3-5 pounds at the crank (that is ALWAYS a good thing), but be aware that there are documented cases of U/D or lightened pulley's going awry.
-Etch

 

I have the Perrin. On a postal scale it weighed 1.25 pounds, and it is stock size so it uses stock belts.
No electrical problems, no dimming.
Better rev-matching and it seems to free up some low and midrange power. I like the effect.

 

for exactly the reason Cobb stated, it can cause problems in SOME cars. I stress SOME. I have a 13lb flywheel, so I've more than made up for it.

San

 

yeah, if you have a pulley dont get a lightened flywheel and vice versa. but it is worth it-it'll improve throttle response and make driving a little more fun.