Does a underdrive pulley really work?
Thread Starter
Pro
Joined: Nov 2005
Posts: 655
Likes: 0
From: Virginia
Does a underdrive pulley really work?
Alright I am going to be ordering a cam here coming up shortly and was thinking that it would be a good time to install a underdrive pulley while I had the radiator out. I have heard some people say that as long as you dont have your ac while racing it doesnt help. Is that true? What type of gains do you get from this. Many companies advertise 10-15 rwhp is that right? 
Burning Brakes
Joined: Aug 2004
Posts: 837
Likes: 2
From: Derry NH
Do a search. This has been discussed recently. Opinions range from zero gain to 7-10 rwhp. Recently a before/after was posted where a pulley and ported TB were the only changes and 15hp/15lbft gains were the result.
If you are going to do it now is the time. (Casem1 kicks himself for not doing it when the steering rack was on the garage floor...)
If you are going to do it now is the time. (Casem1 kicks himself for not doing it when the steering rack was on the garage floor...)
Pro
Joined: Feb 2006
Posts: 616
Likes: 0
From: Vancleave Ms.
Underdrive Pulley
I can't speak about the vettes, but on the mustangs, the underdrive pulleys would ruin the alternator if you sat in stop in go traffic for a majority of the time. Apparently the alternator was not spinning fast enough at an idle, causing it to burn up. They were worth about a tenth at the track, but it wasn't worth it to me after going through several alternators in one year. I will not be going underdriven on my vette. I will build power by other means. 
James
James
Team Owner
Joined: May 2005
Posts: 23,682
Likes: 9
From: Flagstaff Az.
underdrive pulley
I had one for years on my Trans-Am and put one on my C5 when I installed H/C package. I never had any trouble with the alternator and have never heard of one burning up because it ran too slow. It runs the power streering pump and the water pump slower besides the A/C pump. Since the old pulley has to come off there is no additional labor other rhan pinning the crank. Be sure to use a new bolt in the crank.
Drifting
Joined: Sep 2004
Posts: 1,281
Likes: 31
From: Palm Beach Gardens FL
If you're interested I still have some new UD pulleys left which retain the stock a/c belt since the a/c pulley is same as stock size but the accessory pulley is 25% smaller. No noticeable difference with p/s, water temps, or voltage. Cam change is the time to do it, and at this price you can't beat it.
$140 delivered. See my post in FS section for purchase information.
Size of a/c pulley is unimportant while racing or accelerating hard since I would hope your a/c is off and compressor is disengaged. When cruising around town, you probably don't want your a/c underdriven which may noticeably affect the cooling ability.
$140 delivered. See my post in FS section for purchase information.
Size of a/c pulley is unimportant while racing or accelerating hard since I would hope your a/c is off and compressor is disengaged. When cruising around town, you probably don't want your a/c underdriven which may noticeably affect the cooling ability.
Last edited by Dr Chill; May 22, 2006 at 09:45 PM.
Le Mans Master
Joined: Jun 2004
Posts: 6,269
Likes: 50
From: Dallas Texas
St. Jude Donor '06-'07-'09-'10
Originally Posted by Dark-Knight
Yep, they do work and the best time to install is with cam replacement. I've had mine for 2 years and not a lick of problems.
With a cam your idle will be higher anyway, also the smaller pulley would compensate for the higher revs. 
Racer
Joined: Aug 2005
Posts: 277
Likes: 6
From: Raleigh NC
Originally Posted by mean lx
I can't speak about the vettes, but on the mustangs, the underdrive pulleys would ruin the alternator if you sat in stop in go traffic for a majority of the time.
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