I have a 93 LT1, and just recently I decided to purchase an underdrive pulley for the quicker revs and lighter rotating mass rate....at least this is what I have gathered as the benefits from online research.

While doing this research, I came upon a few common issues that seem to plague some F-body owners with their own applications. One, was that many recommended an overdrive pulley as well - you apparently need this pulley because the amount of voltage that your alternator will receive (once the underdrive pulley is on and your car is running at idle)....will be significantly reduced. The overdrive pulley application solves this problem be providing a claimed "32% more power to the alternator". So I made an extra investment, and bought the overdrive pulley. The other issue was that when going to put the serpentine belt back on once the underdrive was one...many also found that the belt was too long. They say that you will need a belt that its apx. 1.5" inches shorter in length.

Can anyone help me out, please? I would very much appreciate it.

 

Most of the "under drive pullies" are add-on units that sandwich between the stock damper and the crank hub. That will add rotating mass. You used to be able to get an integrated damper/UD pulley from ASP, but they may have stopped making it.

You might want to look at the dyno test on the ws6.com website... I think he saw a peak HP gain of 0.70HP, and more "average" HP. There's not much spinning on the LT1 serpentine belt, since it doesn't drive the water pump or the AIR pump. Adding the overdrive alternator pulley may help keep the system voltage up, but you're giving back some small part of the small amount of power saved by the U/D setup.

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

Based on my experience with the ASP 23% U/D crank + 15% U/D alternator, there just isn't enough power gain to justify the use of the U/D pullies.

 

Can't say for certain: I have the March 2-pully sandwhich system. It did require a specific belt so I don't doubt that your system will require a different one also, but by putting on an OD and a UD I don't know whether someone is going to be able to tell you the exact belt to use.

I personally have not experienced any problems and even (probably just in my mind) believe it provides a tad better throttle response, which is nice even if no HP gains .i.e the quicker response to my power band the better in my opinion. If I were you I'd get rid of the OD and do the UDs only, or just not do anything.JMHO

 

I got the asp underdrive balancer and put it on first. I didn't like the way the alt was reading at idle and no programming to raise idle so put the overdrive alt on and got the voltage back up.
There are two ways these pulleys can help. One is by turning things slower. As injuneer has said not much on the lt1 to turn slower compared to other cars like the ls1s.
A second benefit is if they are lighter than the stock balancer which never weighed the asp balancer but think it is lighter. This lighter reciprocating weight at the end of the crank might make some power just from being lighter and might help the car rev faster.

I also think my car does rev a bit quicker but it could easily be in my mind. I will keep the pulley on there as it looks to be a very high qualilty piece. I also have an asp underdrive balancer on my ls1.