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SR Performance Underdrive Pulleys; Black (Late 01-04 GT)

Item 525575
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      Review & Installation Video

      Hey, guys. Stephanie with, here with a review of SR Performance underdrive pulleys for late 2001 to 2004 GT Mustangs. You're going to want to check out the SR Performance underdrive pulleys if you're looking to free up a touch of horsepower in a fast, easy, and very affordable way. The SR Performance costs the least out of any pulley option, and the theory behind underdrive pulleys is that the factory pulleys require a lot of energy. Instead of lightweight aluminum pulleys like these here, reduce the amount of parasitic drivetrain loss, by cutting down on the amount of power that it takes to run the accessories, like the water pump, alternator, and AC compressor. Some people mention noticing a difference after installing these underdrive pulleys. Underdrive pulleys are only a good idea if you plan on keeping your car NA. So just keep that in mind when you're figuring on your future plans. The install for these is going to be an easy one out of three wrenches on the difficulty meter, and you can plan on spending two hours to get the job done. So the engine uses its own power to rotate the serpentine belt, starting at the crankshaft. This pulley then uses the engine's power to rotate the rest of the pulley. So when you reduce the size of the crankshaft pulley, it'll require less energy to rotate the accessories. The pulleys on this side are lightweight aluminum, which means that they'll require even less energy to rotate. This set is powder-coated black, but SR Performance also sells a polished set too, if you prefer the look of those instead. The polished pulleys will cost about $20 more, though. So just keep that in mind. This kit is going to include the crank pulley, the water pump pulley, and the alternator pulley, as well as the hardware to get these installed. The nice thing about these, they're going to free up the power that the engine is currently using to rotate these pulleys, but you won't sacrifice the effectiveness of the accessories. So your water pump and your alternator will still function perfectly. They'll just require less power from the engine to operate. The only time you can see issues is if you have an aftermarket sound system and upgraded alternator. These items are more taxing on the car system, and require more work from the alternator. So if that's the case, I'd recommend steering away from underdrive pulleys. But for those of you that don't have that setup, these will reuse the stock belt. So you won't have to get a different-sized belt, which will make it easier when you need to replace your belt down the road. When it comes to fitment, adjust to make sure you're shopping for the correct year range here. This kit is for the late '01 to '04 GTs with the short water pump. Halfway through '01, Ford changed some things in production. So if you have an early '01 model, you need to pick up the other pulley set. The older water pump style, up until mid-'01, had a longer shaft, and will need a different water pump pulley because of this. As far as price, you're looking at a touch over $100 for this kit. It's the most affordable pulley kit currently at this time. Don't forget, you do have the choice of the SR Performance polished pulley kit if you didn't want the black set, or you have the choice of another brand, like BBK or Steeda. The install here is easy, and I'm going to call it a one out of three wrenches on the difficulty meter. You can expect to spend about two hours getting the install done, and you just need some basic hand tools to get the job done. You need to release the tension on your serpentine belt and set it aside. From there, it's a matter of unbolting the factory pulleys and replacing them with the underdrive pulleys from SR Performance. Once they're bolted on, release the tension pulley again and put the serpentine belt back on. You need to make sure it's on properly, following the diagram usually located on the rad cover. Wrapping things up here with the SR Performance underdrive pulleys, these pulleys are for the late '01 to 2004 Mustang GT, and you can check them out more online right here at

      Product Information

      Features, Description, Reviews, Q&A, Specs & Installation


      • Free Up 10-15 Horsepower
      • Complete 3 Piece Kit
      • Durable, Lightweight Aluminum
      • Black Powder Coated Finish
      • Premium Quality Construction
      • Fits Late 2001-2004 GT Mustangs


      Free Up Horsepower. A set of SR Performance Underdrive Pulleys reduce parasitic drivetrain loss by cutting down the amount of power your accessories take up, these underdrive pulleys will free up 10-15 horsepower, without sacrificing cooling and charging functionality of your Pony.

      Premium Quality Construction. CNC-machined from lightweight aircraft grade quality aluminum alloy for strength and durability, these SR Performance pulleys feature a gloss black powder coated finish for aggressive good looks and long lasting corrosion resistance.

      Easy Installation. These SR Performance Mustang Underdrive Pulleys installs quickly and easily in under 2 hours with no modifications required.

      Application. This SR Performance 3-Piece Aluminum Underdrive Pulley Kit is designed for use on Late 2001 to 2004 GT Mustangs equipped with the SOHC 4.6L V8 engine and the a short water pump (bowed in face). Reuses factory 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.

      SR Performance

      Fitment: 2001 2002 2003 2004 Details

      MPN# 525575

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (34)

      Write a Review

      Ratings Summary

      4.3 out of 5 overall rating from 34 customers

      Installation Time: Afternoon

      Installation Cost: $100-$250

      • December 06, 2019

        1 2004 GT - viprk24 Installation Time: Afternoon

        Terrible product.

        Installed it on my car all was well, engine started shaking at idle, took it to a shop who reinstalled it and couldn't get it to stop. Threw em in the trash.

        Helpful (1)
      • December 02, 2019

        5 2003 GT - PWGRACING Installation Time: Full Day

        The Pulleys

        I love it. I like color black makes the motor look sharp.

        Helpful (0)
      • September 29, 2019

        5 2002 GT - Dingo Installation Time: Less than 1 Hour

        Nice improvement for the money

        A friend did the install. He has tools, crank puller, and could use the extra cash for his car parts. Just drove from 1 side of neighborhood to the other. Small burn out near his home and quick throttle kick on way home. Could tell a performance increase within 1/2 mile. Worth ever penny spent

        Helpful (0)
      • August 11, 2018

        4 2004 GT - PaulS Installation Time: Less than 1 Hour

        Easy install definitely worth it.

        I had a noticeable difference in my low end power and especially with my a/c on. (Still a loss of power but not as bad) the install took about 1 hour start to finish. You WILL need a impact gun to removed alternator pully.

        Helpful (1)
      • July 03, 2018

        5 2003 GT - RonnieS

        Not yet installed...

        But that’s due to my own lapse in time management. The pulleys are insanely lightweight and are machined perfectly!!! As soon as I get my bigger throttle body, plenum, intake manifold and exhaust I’m going to do it all in one shot and go from blah to beast! Turnaround time was not at all like some of the comments but maybe it’s product availability. Three days and an awesome AM decal!

        Helpful (3)
      • June 28, 2018

        1 1998 GT - GordonB Installation Time: Full Day

        They suck

        I don't recommend that anyone who owns a mustang gt 4.6l to buy SR Under Drive PULLEYS THE CRANK PULLEY DON'T FIT AT ALL THAT'S A FACT NOT MY PERSONAL OPINION BUY THE STEEDA PULLEYS BUT YOU ARE NOT GOING TO GET ENOUGH power from PULLEYS

        Helpful (3)
      • April 09, 2018

        5 2002 GT - Sickgt01 Installation Time: Afternoon

        Good for the price

        Got them for my 01 GT automatic they were good so I decided to get them for my 02 Manuel only problem is I had to buy a shorter water pump other than that they're good

        Helpful (4)
      • February 14, 2018

        3 2001 GT - TonyG Installation Time: Afternoon

        Failed me on the hardware

        The pulleys are good quality and do the job regarding performance. That said, the hardware supplied should have matched the OEM standard for hardness. The crank pulley bolt OEM was a 10.9 which is equivalent to a grade 8 standard bolt, case hardened. The supplied bolt was an 8.8 or grade 5 standard. I ended up breaking the bolt in the crankshaft. Probably one of the top three worst nightmares when doing engine work. Thank God I was able to extract the bolt w/o damaging the crank but wasn't until I took the whole nose of the car off to gain straight access to it. Much too soft a bolt for a crank bolt. They need to at least supply the OEM bolt with the kit. Be careful!

        Helpful (10)
      • December 28, 2017

        5 2004 GT - RUDY Installation Time: Shop Install Installation Cost: 0-$100


        Took 1 1/2 hours of install at the mechanics ,car pulled and I felt the power of it real quick ,paid 50$

        Helpful (2)
      • October 03, 2017

        1 2003 GT - DavidN Installation Time: Afternoon

        spend the money and buy the one piece!!

        SPEND THE $ AND BUY THE ONE PIECE LIKE THE STEEDA. I bought this as a quick add on. I could not get the lower pulley mated together at all. I had it apart three different times to get it right. It broke the bolt when tightened at 12 pounds (Im sure it was weakened by removing it three times)..also the top pulley would not fit dispite what the instructions said about the two spacers. American muscle was great and sent me another one. got it on the car and it wobbled like crazy...and yes it was put together properly....I sent it back and bought the steeda...MUCH better product with the single pulley and not the piggy back style. spend the extra $ if you want to do this upgrade.

        Helpful (6)

      Questions & Answers (5 answers)

      5 Top Rated Questions

      So the harmonic balancer just bolts to the pulley correct? Because i heard it was bad for the crank is this true?

      • The SR Performance Underdrive Pulleys will use a piggyback style crank pulley, retaining the OEM balancer. This allows the factory balancer to work as intended when using underdrive pulleys and will have no ill effect on the crank.

      Helpful (0)

      Are these California legal?

      • These SR Performance under-drive pulleys are California legal.

      Helpful (0)

      would this fit 3.8l mustang 99

      • These SR Performance Underdrive Pulleys would not fit your 3.8L, 1999 Mustang, I apoligize. We unfortunately do not currently carry a pulley kit for your year-model Mustang.

      Helpful (0) Show 1 more answer

      What size belt is needed?

      • These underdrive pulleys are able to reuse the stock belt. You do not need to buy a different size.

      Helpful (0)

      Does Item# 525575 fit an 04 4.6L Crown Vic Police Inter. motor?

      • While there are many similarities, we unfortunately are not able to confirm fitment on your vehicle, I apologize.

      Helpful (0)
      Post Your Question

      Installation & What's in the Box

      Installation Info

      What's in the Box

      • (1) Crank Pully
      • (1) Water Pump Pully
      • (1) Alternator Pully
      • (4) Bolts
      • (3) Washers
      • (2) Spacers
      • (1) Instruction Sheet

      Tech Specs

      Underdrive Pulley Specifications
      Year/Model:Late 2001 to 2004 GTManufacturer:SR Performance
      Material:AluminumFinish:Black Powder Coat
      Crank Pulley: PiggybackSFI Certified:No

      Will It Fit My Mustang

      • GT - 01, 02, 03, 04

      Fits GT Mustangs with the short water pump with a bowed in pulley.

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