I've heard people either really like them or hate them is it a good bolt-on mod??

 

Had it on my old 6 speed Z28.....not worth it IMHO. I had to replace the battery every year like clock work. No SOTP increase and minimal on the dyno.
Mike

 

IMO, not worth it. Save the $$ and spend it on something else.

 

LT1 dyno results:

http://www.ws6.com/mod-2.htm

There are several different types and ratios of U/D pullies. The best setup is an integrated damper and U/D pulley, completely replacing the stock damper. Minimizes weight on the end of the crank. The "sandwich" type add-on pullies add extra weight.

Then there's the ratio of the U/D crank pulley, ranging anywhere from 23-40%. The larger the number, the more it slows things down, and the more problems you'll have with the alternator output at idle.

Then there's sets, with an alternator pulley included. Get a set with an O/D alternator pulley (e.g. - March "Power & Amp" series), to speed the alternator back up.... charging problems solved, but you just gave back some of that 0.70 (peak) rwHP. Get a set with an U/D alternator pulley, and things just get worse as far as charging.

The charging issue will be a bigger problem with the A4 tranny, since the factory idle speed is lower (550rpm in "drive" vs. 800rpm for the M6).

I had an ASP integrated 23% UD crank pulley, and the 15% U/D alternator pulley, and had charging problems at idle in heavy traffic with the A/C or brake lights on. Personally..... not worth it.

 

I did some serious research on it and have come to the following conclusion:

Piggyback pulleys just add weight to the rotating assembly. Any underdrive benefit you get is pretty much negated by the weight.

Regular pulleys are going to gain you some, but not much. On most cars, the biggest gain from a pulley set is from the waterpump and power steering. Our waterpumps are mechanical, not belt driven so the gains you see are minimal ( Less than 5 HP across the board ... and peak )

The only real need for a pulley is if you are spinning some serious RPM's or making some real horsepower ( N20, Boost, HC, etc) and in the case, you should be directed towards getting a ATI harmominc balancer ...

There are better bang for the buck mods out there.

 

I don't think it was really worth the $ either. If you do decide to go with it though, I would reccomend getting it from March. They are the only ones that garuntee that you won't loose any voltage to your system.

I also happen to be selling mine from my 95 LT1 for $45 if interested.

 

We're taking mine back off, tired of replacing batteries too.

 

I never had any problems with mine. I just had to take it off when the ATI superdamper/balancer was put on after my D1SC was installed. Then again, mine was from March. I have heard of problems with other brands pulling voltage away like you said.