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SR Performance Underdrive Pulleys (Late 01-04 GT)

AmericanMuscle no longer carries the SR Performance Underdrive Pulleys (Late 01-04 GT). Please check out 1999-2004 Mustang Underdrive Pulleys for an updated selection.
10 Reviews
Our Price

$139.99

  • Item #41130
  • Market Price $159.99
  • You Save 13% ($20.00)
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AmericanMuscle no longer carries the SR Performance Underdrive Pulleys (Late 01-04 GT). Please check out 1999-2004 Mustang Underdrive Pulleys for an updated selection.

Product Videos Customer Photos
Features
  • Gain horsepower
  • Complete kit
  • Durable, lightweight aluminum
  • Brilliant polished finish
  • Premium quality
  • Fits Late 2001 to 2004 GT
Description
Untap Hidden Horsepower. Add some more bite to your GT's bark by reducing the amount of power you're losing to accessories and A/C. When you install this underdrive pulley kit, you'll free up up to 15 horsepower - and it's pretty much all gain and no pain, since you won't sacrifice your charging characteristics or A/C to do it.

Premium Quality.
Don't settle for inferior parts. These premium quality pulleys are made from lightweight aluminum for durability and performance. Made using precise, state-of-the-art CNC manufacturing, you can count on these pulleys to perform at the highest level.

Easy Installation.
This Underdrive Pulley kit installs quickly and easily in under 2 hours with no modifications required.

Application. These underdrive pullies are designed for the Late 2001 to 2004 GT with the short water pump pulley with a bowed in face. Re-uses stock factory serpentine belt.

Technical Note. Midway through the production run for the 2001 model year Ford changed the design of the water pump on the 4.6L engine. The older style pump produced from 1996 to mid 2001 had a longer shaft. In January of 2001 the design of the pump was changed to a shorter shaft. This necessitated a change in the design of the pump pulley.

Click here to see pictures of the different pulley styles.

Mustang Fitment: 2001 2002 2003 2004 Details

What's in the Box
  • (1) Crank Pully
  • (1) Water Pump Pully
  • (1) Alternator Pully
  • (2) Spacers
    Hardware included:
  • (4) Bolts
  • (3) Washers
  • (1) Crank Key
Installation Info
Tech Specs
Underdrive Pulley Specifications
Year/Model: Late 01-04 GT Manufacturer:
Material: Aluminum Finish: Polished
Crank Pulley: Piggyback SFI Certified: No
Fitment
  • GT - 01, 02, 03, 04

Most Helpful Reviews View All

Overall Rating 4.3/5 Write a Review
5/5
Stack Underdrive Pulleys

Got the product and forgot it was a piggy back system, so i was little worried. i installed the water pump pulley with no problem. the alternator pulley was a little more difficult. the instructions had

Read More
Helpful (9) (1)

3/5
good definatley not great

I bought these under drives to put on my mildly modified 03 GT automatic, when i got he part i noticed first off that the pulleys, particularly the crankshaft and alternator pulleys were scratched ad scored

Read More
Helpful (3) (0)

Videos

Customer Photos (2) View All

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Q & A (1 Questions, 1 Answers) Ask a Question

how much does this kit change change the ratio at the crank? What is the diameter of the stock crank pulley and what is the diameter of the BBK? Thanks.

Johns2004GT Year: 2004 Model: GT

Good Question (0) (0)
  • It does not change the ratio at the crank the ratios are changed at the power steering, air conditioning, alternator and smog pump if you have one. They supply a pulley to maintain the rpm at the water pump so you don't over heat. And the HP gain is a bout 5 to 8 HP. Get a tuner or a CAI or both if you really want to feel a increase in power when you hammer it down!!!

    Helpful (0) (0)

    fasteddie64 Year: 2006 Model: GT

    Top 1 Contributor

Answer This Question

Reviews (10) Write a Review

  • 5 Stars .50 50%
  • 4 Stars .30 30%
  • 3 Stars .20 20%
  • 2 Stars 0 0%
  • 1 Stars 0 0%
4.3

out of 5 stars

8 Customers Recommend this Product

Installation Time:Afternoon

  • Performance Gain: 3.833333 3.8/5
  • Fit: 3 3/5
  • Bang For Your Buck: 4 4/5
Filter By Sort By
  • 5/5

    Stack Underdrive Pulleys

    May 09, 2011

    Got the product and forgot it was a piggy back system, so i was little worried. i installed the water pump pulley with no problem. the alternator pulley was a little more difficult. the instructions had nothing in it about using the brass spacers. plus the bigger spacer that i had to use was a little small, so i just filled it out a little and it worked prefect. i wanted to put those 2 pulleys on myself to keep the mechanic's labor down. i then tried to put the belt back on to drive it down to my mechanic and the belt does not fit on the stock crank pulley with the new water pump and alt. pulley. bottom line if u cant install the crank pulley let the mechanic put them all on. and please use the piggy back system and not just the new crank, u will throw off the balance of the engine off if u do not bolt the stock crank and balancer to the new stack racing crank pulley. after all that i did notice a big difference, i did run on the dyno before and after the install. i gained 18 HP and 21 FT-TQ. I think thats awesome gains. i dont have much done to the car. if you want proof email me and ill show you the dyno print outs. i Think its a great product and am recommending it to all my friends. PROOF DOESN'T LIE. canyousayhemi@gmail.com

    jason L.

    Year: 2002 Model: GT Driving Style: Daily Driver

    Helpful (9) (1)

  • 3/5

    good definatley not great

    August 29, 2011

    I bought these under drives to put on my mildly modified 03 GT automatic, when i got he part i noticed first off that the pulleys, particularly the crankshaft and alternator pulleys were scratched ad scored like they were factory seconds, this displeased me due to the fact that the polished aluminum is supposed to be a bit of a cosmetic under the hood. installation was pretty good, the instructions were not helpful, it had no mention of brass spacers, (larger one goes on alternator) and another thing was even with the automatic there is no need for impact tools, a breaker bar will do just fine. the bolts on the harmonic balancer are a bit fragile so be careful torquing them down. i broke one and it was a pain to drill out. extremely dissatisfied with installation. however the performance was decent, the car pins you back in your seat above 3k rpms, enjoyable gain but if i did it again i would go with Steeda

    Slater

    Year: 2003 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 Greenville SC

    Helpful (3) (0)

  • 5/5

    Nice

    January 20, 2011

    Instructions although printed with color photos it is lacking information. I was able to figure it out however. Pay close attention to how far your pulley is away from the alternator because there are different sized bushings which is not mentioned. The stock crank pulley has one key way and one supplied has two. Use plenty of RTV. Other than that everything lined up good and runs true. The video on the tech article supplied by American muscle is for a Steeda kit and is only useful for general information. What do I like... winds up quicker and third gear is now useful. Car pulls harder. If in doubt go for it. Real gain for very little money from Stack Racing. Thanks American Muscle.

    Rock

    Driving Style: Daily Driver

    Helpful (4) (1)

  • 4/5

    Stack Underdrive Pulleys

    February 26, 2011

    Fit and finish on product is great and price is reasonable. Improvement is noticeable at higher RPM's. Instructions are simply adequate. Getting the crankshaft nut off can be difficult so be prepared for that. If you don't have a torque wrench, air tools etc. you might want to just have your mechanic put these on. I have the tools and install only took about 30 min. Don't forget to use the RTV.

    J-Hem

    Year: 2003 Model: GT Driving Style: Daily Driver

    Helpful (3) (1)

  • 4/5

    Good gain for the money!

    August 05, 2013

    Installed in no time! You can feel the difference if you pay enough attention to your car, it's subtle but you can feel it.

    Coolgate

    Year: 2004 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 2 Virginia

    Helpful (1) (0)

  • 5/5

    felt gains right away.

    March 22, 2011

    I liked the product for the look and how easy it was to install. I choice these pulleys for the cost and so far they are running great. felt a gain soon as i put them on.

    Chase

    Year: 2003 Model: GT Driving Style: Daily Driver

    Helpful (1) (1)

  • 5/5

    Great Product!

    December 31, 2012

    I bought these pulleys for my 04 gt, to start the instructions in the box were horrible! the kit comes with 2 brass washers and the instructions say nothing about the washers. for the alternator pulley the brass washer didn't even fit, good thing i work in a machine shop i had to Bore the washer out a good amount (.006") to get it to fit nice and snug. other then that putting them on went smooth. i felt a big difference over 3000 rpm's, you can feel the car throw you in your seat a lot more and i could most defiantly felt a difference. i had NO problems with my battery dying because of the alternator not charging. GREAT product i recommend 100%

    Yellow04gt

    Year: 2004 Model: GT Driving Style: Street / Strip 'Stangs I have owned: 5+

    Helpful (0) (1)

  • 3/5

    its ok

    December 22, 2012

    I bought this underdrive pull set installed it was less than impressed with the outcome so I got a more expensive set from steeda it was much easier to instal no bushings to choose from for the alternator and no need to reuse the stock harmonic balancer as it came with a one price balancer/pully and gained a little more power:)

    bthompson

    Year: 2004 Model: GT Driving Style: Street / Strip 'Stangs I have owned: 2 east texas

    Helpful (0) (1)

  • 5/5

    great price

    January 27, 2012

    These underdrive pullies are a great price and look really good. Well worth the money!

    Spink

    Year: 2004 Model: GT Driving Style: Show 'Stangs I have owned: 1 Schuylkill Haven, PA

    Helpful (0) (1)

  • 4/5

    2004 Mustang GT

    December 22, 2012

    The pulleys are good quality. The performance improvement was very noticable in both throttle response and HP. The only problem is that the alternator pulley is a few hundredths too small for the factory alternator shaft. You need to be able to bore out the pulley slightly and evenly for installation.

    William64

    Year: 2004 Model: GT Driving Style: Race 'Stangs I have owned: 1 Tolland, CT

    Helpful (0) (0)

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