Underdrive Pulleys C5
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
I have always heard the 25% underdrive is more like 6-8 hp. Not a bad hp/$ if you are already changing out your balancer, but it is not worth the effort as a stand alone upgrade. You will also need a shorter serpentine belt ($30) plus a new balancer bolt ($4). Might as well replace the front seal too ($12).
Drifting
Joined: Jun 2002
Posts: 1,945
Likes: 41
From: Corinth TX
Actually I have heard it is anywhere from 8-12rwhp. If you are considering getting it done you may want to get a new cam and put the underdrive pulley on as free labor. They have to pull the underdrive pulley to install the cam. I have one on my car and have nothing but positive things to say about it.
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Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
ASP makes some nice products as does Powerbond. Getting the crank snout pinned while there is a good and cheap thing to do too (added insurance).
Thread Starter
Instructor
Joined: Nov 2007
Posts: 198
Likes: 0
From: Lodi New Jersey/New York
Actually I have heard it is anywhere from 8-12rwhp. If you are considering getting it done you may want to get a new cam and put the underdrive pulley on as free labor. They have to pull the underdrive pulley to install the cam. I have one on my car and have nothing but positive things to say about it.
Melting Slicks
Joined: Sep 2003
Posts: 2,458
Likes: 105
From: Northville Michigan
It will cause your marginal water pump to become even more inefficient. 
It will not allow your alternator to put out the amperage that GM designed it to put out at the low RPMs we see in 5th and 6th gear.
It will reduce the ability of the power steering pump to keep up with your turning demands.
IMHO - Underdrive pulley are not a well thought out idea.
It will not allow your alternator to put out the amperage that GM designed it to put out at the low RPMs we see in 5th and 6th gear.
It will reduce the ability of the power steering pump to keep up with your turning demands.
IMHO - Underdrive pulley are not a well thought out idea.
Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
It will cause your marginal water pump to become even more inefficient.
It will not allow your alternator to put out the amperage that GM designed it to put out at the low RPMs we see in 5th and 6th gear.
It will reduce the ability of the power steering pump to keep up with your turning demands.
IMHO - Underdrive pulley are not a well thought out idea.
It will not allow your alternator to put out the amperage that GM designed it to put out at the low RPMs we see in 5th and 6th gear.
It will reduce the ability of the power steering pump to keep up with your turning demands.
IMHO - Underdrive pulley are not a well thought out idea.
BTW, alternators put out maximum amount at a very low rpm. That's the main reason automotive electrical systems went over to them over the previous conventional generators designs many years ago. Most, if not all, are "all in" by 1000 to 1200 rpms. Also wasn't aware we had "marginal water pumps" either.
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Been running a 25% underdrive Powerbond for over a year now, no cooling/charging/steering issues whatsoever.
Engineer scare tactics are always wonderful...but more useful are the hundreds of reviews from people actually using and enjoying the product.
One look at the quality differences between stock and aftermarket pulleys, and there is no doubt which one you'd want on your car.
I wouldn't bother with the effort needed to install one though, unless you are already in there for a cam swap, or your stock pulley is junk and wobbling (not uncommon).
Engineer scare tactics are always wonderful...but more useful are the hundreds of reviews from people actually using and enjoying the product.
One look at the quality differences between stock and aftermarket pulleys, and there is no doubt which one you'd want on your car.
I wouldn't bother with the effort needed to install one though, unless you are already in there for a cam swap, or your stock pulley is junk and wobbling (not uncommon).
Want to buy one since I'm doing a cam and heads and headers and intake manifold and LS6 ported oil pump swap
Le Mans Master
Joined: Aug 2001
Posts: 8,145
Likes: 1
From: Bradenton FLORIDA
Not experiencing any negative symptoms with my 25% underdrive Powerbond pulley.
BTW, alternators put out maximum amount at a very low rpm. That's the main reason automotive electrical systems went over to them over the previous conventional generators designs many years ago. Most, if not all, are "all in" by 1000 to 1200 rpms. Also wasn't aware we had "marginal water pumps" either.
BTW, alternators put out maximum amount at a very low rpm. That's the main reason automotive electrical systems went over to them over the previous conventional generators designs many years ago. Most, if not all, are "all in" by 1000 to 1200 rpms. Also wasn't aware we had "marginal water pumps" either.
Been doing these for years & running them on my personal cars....never an issue.
like 15 hp!
