more input all please 
Underdrive Pulley
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From: Fort Collins, Colorado Springs
Underdrive Pulley so i cracked the lip of my harmonic balancer tryin to put it on so i suppose i should replace it what does everyone think about underdrive pulleys i have heard both ways good or bad?
They are worth about a tenth at the track or about 7 RWHP on a dyno. As long as you don't run some killer stereo at idle speeds for long periods of time, there generally are no ill effects. Your accessories can also last longer since they are turning slower.
We sell the ones by ASP.
We sell the ones by ASP.
Thread Starter
TECH Regular
iTrader: (5)
Joined: Dec 2007
Posts: 409
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From: Fort Collins, Colorado Springs
so whats the difference between the two asp pulleys you have besides the $50 also how should i set it up so i dont have a charging issue also will it affect the water pump at all as it will slow its rotations
While you are looking for an underdrive pulley, may I suggest you get the proper tool to draw the pulley down on to the crank so that this doesn't happen again? That isn't exactly a cheap mistake to make...there is a guy that makes them in the Tools and Fabrication section of this forum.
Here's my $.02. A 25% underdrive pulley should be good for around a tenth in the quarter mile and roughly 6-10 rwhp. I would recommend that you purchase a pulley with the higher retainer around the edge (as this help keeps your belts from walking off of the pulley). The only way you should encounter a charging problem is if you have a sound system that requires a good bit of power (external amps, sub, etc.). In my experience, I put UD pulleys on my Corvette (A4) and it worked like a charm. I'm getting the pulley installed on my SS on Monday, so I'll let you know how that works out.
ASP sells two variations for the LS1 Fbodies. The first is just a underdriven crank pulley. The 2nd is a kit with an underdriven crank pulley AND an underdriven alternator pulley. We recommend going with just the crank pulley as that provides the majority of the improvement and doesn't affect charging as much.
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I put a 25% UD ASP pulley on my T/A and it gave a little quicker revving but no seat of the pants improvement. Then again I was already at 400RWHP so I didn't expect to feel anything. I did notice that when coming down to idle that the headlights would dim just a little bit.
To install the new pulley you just need a longer crank bolt to pull the pulley on. When I did my cam swap and still had my stock pulley I actually heated up the center of the stock pulley with a propane torch and then it slid on like butter.
