under drive pulley
Thread Starter
Race Director
Joined: Mar 2006
Posts: 10,477
Likes: 4
From: lockport n.y
under drive pulley
what is involved to install an under drive pulley and what kind of HP gains can I expect on 02 a4 fast92/92 cam heads lth high flow cats stingers and tune thanks for any info
Safety Car
Joined: Apr 2007
Posts: 3,582
Likes: 137
From: SoCal CA
Here is ATI's instructions but they dont tell you all the bs you have to get by or remove like the whole steering rack.
http://www.andersonperformance.net/C...er_Install.pdf
http://www.andersonperformance.net/C...er_Install.pdf
Melting Slicks
Joined: Nov 2003
Posts: 3,011
Likes: 9
From: Dublin GA
I would personally NEVER install an underdrive pulley unless I was already in there doing a cam change. There just isn't enough real dyno evidence of rwhp gains to warrant the major PITA 
of removing the steering rack and pulling the balance (and of course installing new seals etc.)
I have one laying around in my shop that I could put on my wife's car, but wouldn't dream of doing it unless we install a cam
There are a lot more low $$ mods you can do and get proven gains (not gains the vendor claims)
of removing the steering rack and pulling the balance (and of course installing new seals etc.)I have one laying around in my shop that I could put on my wife's car, but wouldn't dream of doing it unless we install a cam
There are a lot more low $$ mods you can do and get proven gains (not gains the vendor claims)
Tech Contributor
Joined: May 2008
Posts: 2,843
Likes: 16
From: Howell Michigan
St. Jude Donor '09-'10-'11
I would personally NEVER install an underdrive pulley unless I was already in there doing a cam change. There just isn't enough real dyno evidence of rwhp gains to warrant the major PITA of removing the steering rack and pulling the balance (and of course installing new seals etc.)
I have one laying around in my shop that I could put on my wife's car, but wouldn't dream of doing it unless we install a cam
There are a lot more low $$ mods you can do and get proven gains (not gains the vendor claims)
of removing the steering rack and pulling the balance (and of course installing new seals etc.)I have one laying around in my shop that I could put on my wife's car, but wouldn't dream of doing it unless we install a cam
There are a lot more low $$ mods you can do and get proven gains (not gains the vendor claims)
Engine driven accessories like the alternator, water pump, and power steering pump have a fairly linear curve when it comes to sucking power from the engine. Changing drive ratio is much like shifting to a lower gear allowing faster acceleration. One of the biggest advantages that most people over look is the inertia factor. By using an underdrive pulley, the alternator isn’t spun up as high as with the stock pulley ratio. The alternator is the largest inertia load of all accessories. It plays a major factor on how rapid the engine can rev, much like the inertia of a light versus heavy flywheel. In simple terms it plays a big factor on throttle response. If performance is your game or desire, and you don’t expect to drive your car when it is -40 deg’s outside, then going to an underdrive balancer might be a reasonable choice to gain performance.
Last edited by Eric D; Nov 28, 2009 at 07:36 PM. Reason: miss spelled word fix..
Melting Slicks
Joined: Nov 2003
Posts: 3,011
Likes: 9
From: Dublin GA
I stick to my statement "Show me the money"
I have seen three attempts at dyno "test" on underdrive pulleys and the MOST I have ever seen was 6hp (one showed 1 hp) That is not enough for me to bother with
I have seen three attempts at dyno "test" on underdrive pulleys and the MOST I have ever seen was 6hp (one showed 1 hp) That is not enough for me to bother with
Burning Brakes
Joined: Oct 2004
Posts: 931
Likes: 35
From: Rowlett, Texas
Well, I can't give any dyno comparo, since I also wouldn't think of messing with a pulley swap unless a nice cam went in also. But, I do have experience on the effects of a 25% pulley on the accessories.
- Water temp went up from 183 to 185 when freeway cruising steady-state in 6th gear in 100-degree weather in Texas. No noticeable change in stop-go.
- AC showed no detectable change in the hot Dallas summer.
- Charging circuit unaffected, but I rarely play the radio.
- Steering effort displays a very slight tug when starting off from a rest and turning the wheel sharp - like backing out the drive and heading out down the street. Perfectly acceptable.
- My ASP pulley has absolutely zero wobble, much better than the stock unit.
I feel certain all my accessories, belts, and the infamous idler pulleys will last longer - just seems logical.
One last thing - I did a lot of small mods to my C4 Vette, like exhaust, intake, chip, etc. The only mod I could definitely feel was the underdrive pulley.
DG
- Water temp went up from 183 to 185 when freeway cruising steady-state in 6th gear in 100-degree weather in Texas. No noticeable change in stop-go.
- AC showed no detectable change in the hot Dallas summer.
- Charging circuit unaffected, but I rarely play the radio.
- Steering effort displays a very slight tug when starting off from a rest and turning the wheel sharp - like backing out the drive and heading out down the street. Perfectly acceptable.
- My ASP pulley has absolutely zero wobble, much better than the stock unit.
I feel certain all my accessories, belts, and the infamous idler pulleys will last longer - just seems logical.
One last thing - I did a lot of small mods to my C4 Vette, like exhaust, intake, chip, etc. The only mod I could definitely feel was the underdrive pulley.
DG
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Banned Scam/Spammer
Joined: May 2007
Posts: 15,685
Likes: 1,330
From: Machineguns, because I don’t compromise
5-9 rwhp on a dyno.
On an F-body it's a good mod even if you're not changing the cam.... on the Corvette it's much more work pulling the steering rack.
Save that mod for when the cam is being changed.
On an F-body it's a good mod even if you're not changing the cam.... on the Corvette it's much more work pulling the steering rack.
Save that mod for when the cam is being changed.
Safety Car
Joined: Jul 2005
Posts: 3,572
Likes: 9
From: Jackson Tn
St. Jude Donor '06-'07-'08-'09
