Underdrive Pulley Mod???
Thread Starter
Le Mans Master
Joined: Apr 2000
Posts: 9,725
Likes: 229
From: Motor City Vettes Ringleader
SE Michigan Coordinator
CI 3, 4, 5, 6, 10 Veteran
St. Jude Donor '09-'11,-'13-'14-'15
NCM Sinkhole Donor
Underdrive Pulley Mod???
ASP Underdrive Pulley Kit? Is This mod worth the cost?
For those of you that have had this mod on your car for a while, what would you say are your pros and cons, compared to stock.
If you had to do it again, would you, or would you pass?
Thanks for your input
For those of you that have had this mod on your car for a while, what would you say are your pros and cons, compared to stock.
If you had to do it again, would you, or would you pass?
Thanks for your input
Racer
Joined: Feb 2005
Posts: 484
Likes: 0
Safety Car
Joined: Oct 2000
Posts: 4,949
Likes: 10
From: Monticello MN
Originally Posted by The Kid
Ed
Racer
Joined: Mar 2003
Posts: 279
Likes: 0
I don’t have one for the Vette but I have done one for my Nissan 300ZX several years ago. If there was any gain, it was not noticeable. I will not do it again. To me, any mods other than H/C, supercharger/turbo, Nitrous, or bigger displacement will not have very noticeable gains. I would save the money and do one or more of those instead. It’s just my 2 cents. 
Le Mans Master
Joined: Nov 2003
Posts: 8,004
Likes: 250
From: Tampa Fl
St. Jude Donor '12-'13-'14
Originally Posted by GOOSE JR.
I have run the underdrive pulley for about a year with no problems. The gain is not worth the effort by itself but if your installing a cam and have it off then yes it would be worth changing.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
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
Drifting
Joined: Jan 2000
Posts: 1,660
Likes: 9
From: Charlotte, NC
I had the ASP pullies put on my ’98 SS Camaro when I had the cam installed. I’ve seen dynos of F-bodies with just the ASP pulley changed and it would add between 4-8 rwhp aross the entire rpm range. It is a good mod, but the labor involved is difficult and you would only want to swap pulleys if you had to take the stocker off for some other reason.
I’ve heard A4s can have charging problems if they use both the crank pulley and the alternator pulley, but the M6s could use both with no problem (because the M6s have a higher rpm idle which provides more charging to the battery). The engine seemed to rev up and down faster once the pulley was installed and given the loss of power in the low rpm range (under 1,200 rpm) with the cam install, the pulleys probably made the car a bit easier to start off from a light.
Make sure the install is done right and be sure they use a new crank bolt when installing (you can't use the old crank bolt!!).
I’ve heard A4s can have charging problems if they use both the crank pulley and the alternator pulley, but the M6s could use both with no problem (because the M6s have a higher rpm idle which provides more charging to the battery). The engine seemed to rev up and down faster once the pulley was installed and given the loss of power in the low rpm range (under 1,200 rpm) with the cam install, the pulleys probably made the car a bit easier to start off from a light.
Make sure the install is done right and be sure they use a new crank bolt when installing (you can't use the old crank bolt!!).
Pro
Joined: Oct 2002
Posts: 586
Likes: 0
From: Idabel OK
Originally Posted by FASST LN
I had the ASP pullies put on my ’98 SS Camaro when I had the cam installed. I’ve seen dynos of F-bodies with just the ASP pulley changed and it would add between 4-8 rwhp aross the entire rpm range. It is a good mod, but the labor involved is difficult and you would only want to swap pulleys if you had to take the stocker off for some other reason.
i totally agree
Former Vendor
Joined: Mar 2004
Posts: 1,518
Likes: 7
From: Valencia CA
If your stock dampner finds its way off the end of your crankshaft (such as a H/C swap etc.), just DO IT. It does in fact free up some HP to the tire by reducing the parasitic losses of turning your accessories at full speed. It's $250 for 5 RWHP....which in the Corvette world, is decent HP per dollar and in my opinion represents a good bang for the buck if your searching for more power and performance.
Tony M.
Tony M.
Drifting
Joined: Nov 2003
Posts: 1,539
Likes: 3
From: South al
i am putting a UD pulley on my car & i looked @ asp they are on back order they are always on back order cuz they dont make but 50 @ 1 time theres another company out there called pioneer there a australlian based co. i was also in the market for an ud cuz i am installing a cam went to my local speed shop he told me about this co he can get the ud for 200.00 there out of pensacola,fl speedunlimited is the name the number is1-800-874-8655 heres another # its 850-455-1341 ask for rob mine is on the way no waiting for asp to make another batch & waiting on a back order boy thats aggravaating hope i have helped someone with this info btw i think asp pulleys sell for 230 u will save by going thru this outfit gl
