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SR Performance Underdrive Pulleys (05-10 GT)

Market Price $186.99 You Save 12% ($22.04)
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  • Item 41131
  • MPN# 41131

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    Features, Video & Details

    • Free Up Horsepower
    • Complete Kit
    • Durable, Lightweight Aluminum
    • Brilliant Polished Finish
    • Premium Quality
    • Fits 2005-2010 GT and Bullitt Mustangs

    Review & Installation Video

    Review & Install Video

    Hey I’m Justin with, and I’m breaking down these underdrive pulleys from SR Performance, fitting the 4.6L V8 motor found in all 2005-2010 Mustang GTs. Engine accessories like the AC compressor, water pump and alternator can really rob your car of horsepower, a great example of how much power an accessory can eat up is whenever you turn your cars AC on and instantly it feels a little more sluggish. This is referred to as parasitic drag. The idea of an underdrive pulley is to turn the different accessory pulleys at a different speed, using these different sized pulleys thus requiring less power from the motor to drive each accessory. This reduction in drag on the crank shaft should allow the motor to operate more efficiently, and essentially equate to more power at the rear wheels. The SR Performance kit includes a new water pump pulley along with a brand new crank pulley, and the hardware needed for the install. Both pulleys are SF5 certified and are constructed using lightweight aluminum. As an added bonus, that bright polished finish is sure to look good under the hood as well. As far as the install is concerned, you just want to leave yourself a couple of hours to get both pulleys installed. Ideally, you should have a torque wrench on hand as well as some high temp RTV sealant and a breaker bar for that crank pulley bolt. This isn’t the hardest job in the world, but if you’ve never attempted it before, I really suggest watching the detailed instruction video located on this product page before getting started on the install. So be sure to check out the SR Performance underdrive pulleys right here at

    Untap Hidden Horsepower. Don't let your accessories and A/C drain power from your GT or Bullitt Mustang. By replacing your factory pulleys with this SR Performance Underdrive Pulley Kit, you'll free up to 15 horsepower that's currently being drained by your accessories and put it back where it belongs - under your right foot. Best of all, you won't affect your vehicle's charging or cooling capacity in the process.

    SFI Certified Design. If you're ready to take it to a track, you'll rest easy knowing these SR Performance Pulleys are SFI Certified.

    Premium Quality. Don't settle for inferior parts. These premium quality SR Performance 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 SR Performance Mustang Underdrive Pulley Kit installs quickly and easily in under 2 hours with no modifications required.

    Application. These SR Performance Underdrive Pulleys are specifically designed for use on the 2005 to 2010 GT and 2008 to 2009 Bullitt Mustangs.

    Fitment: 2005 2006 2007 2008 2009 2010 Details

    What's in the Box
    • (1) Crank Pulley
    • (1) Water Pump Pulley
    • (1) Crank Bolt
    • (1) Instruction Sheet
    Installation Info
    Tech Specs
    Underdrive Pulley Specifications
    Year/Model: 2005-2010 GT Manufacturer: SR Performance
    Material: Aluminum Finish: Polished
    Crank Pulley: One Piece Crank SFI Certified: Yes
    Will it fit my Mustang?
    • Bullitt - 08, 09
    • GT - 05, 06, 07, 08, 09, 10

    People Who Bought This Item Also Bought

    Most Helpful Reviews

    Great Bang for Your Buck

    The pulleys look good,installation was a piece of cake,the only recomendation for the install is to get a M8-1.25x2 bolt to replace the alt stud,instead of cutting the stud for the waterpump pulley to ...

    Read More
    Helpful (11)

    Fuel Millage

    The day after the install of the new pulleys, I took the car for a trip. I got 26- 28 mpg! I have never seen that before, so it clearly made a difference. I have since done a few more bolt-ons and together ...

    Read More
    Helpful (11)

    Overall Rating 4.7 out of 5 stars
    Read All 87 Reviews

    Customer Photos (33) Submit Your Photo

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    14 Questions / 8 Answers

    Ask a Question

    Low accessories power? How much power will this take away from the accessories? Is it a noticable difference or not?


    • I had the same worries, but after the install I checked the output voltage on the alternator and all around the vehicle before and after the installation and there was no power shortage at all, and for the performance the pony revs way more faster......and it looks cool.....


    Show 2 more answers Helpful (6)

    can i use this for the Mustang 2006 V6??


    • These pulleys will not work for the 2006 V6 Mustangs.


    Helpful (1)

    Work with on a V6? I've seen on a few forums people were saying to increase HP on a V6 to get an underdrive pulley, but the only ones on here are for GT's. Was just wondering if these would work on a V6.


    • I would only get pulleys that are meant for your specific engine. Could cause problems otherwise and I doubt they'd fit.


    Helpful (1)

    What's the diameter of the crank pulley?


    • The diameter of the crank pulley will be about 5 1/4".


    Helpful (0)

    How much will power steering be reduced? I understand it will lose a bit but like. How bad. If my steering is gonna be hard at low speeds then i wonder if its worth the extra horses. Let me know any downsides anyone notices. Thanks!


    • Hello! You should not notice much of any difference from the SR Performance Underdrive Pulleys in terms of power steering. The pulleys focus more on accessories and a/c


    Helpful (0)

    What accessory does this replace? Does it replace the a/c?


    • These SR Performance Underdrive Pulleys replace the crank pulley, and the water pump pulley.


    Helpful (0)

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    Customer Reviews (87) Write a Review

    Overall Rating 4.7

    out of 5 stars

    Installation Time:Afternoon

    Installation Cost:0-$100

    • Performance Gain 4.35 4.4
    • Fit 4.851852 4.9

    • 5/5

      Installation Time: Afternoon

      April 03, 2012

      Great Bang for Your Buck

      The pulleys look good,installation was a piece of cake,the only recomendation for the install is to get a M8-1.25x2 bolt to replace the alt stud,instead of cutting the stud for the waterpump pulley to clear. Noticed a slight power gain. Great product for the price.


      Year: 2006 Submodel: GT N. Myrtle Beach SC

      Helpful (11)

    • 5/5

      Installation Time: Afternoon

      January 27, 2012

      Fuel Millage

      The day after the install of the new pulleys, I took the car for a trip. I got 26- 28 mpg! I have never seen that before, so it clearly made a difference. I have since done a few more bolt-ons and together they have turned the car into a real handful! When I speed shift into second, hold on becouse she is going to pull sideways and then bark a hard 3rd! The pulleys were easy to install. I have already recommended that my friends to do the same. Cannot wait until the track opens to see the new times. Fastest pass has been 13.7 totally stock.


      Year: 2010 Submodel: GT Anderson Texas

      Helpful (11)

    • 3/5

      Installation Time: Less than 1 Hour

      March 05, 2012

      Price wise, better then other pulleys, power is ok

      I work at Mustang Specialties, I purchase this set for my personal 09 GT did a before and after dyno. made 316rwhp before the install. Install went smooth and everything fit no problem and looks great. went ahead and dyno'd the car after the install same day just an hour later. car made 320rwhp with the pulley install. So with no other changes at all on the car what so ever this car will give a dyno proven 4rwhp. For me its not worth it, the car on nitrous still ran the same time and mph 11.5X@118-119


      Year: 2009 Submodel: GT

      Helpful (10)

    • 3/5

      Installation Time: Less than 1 Hour

      December 01, 2011

      Great just a few things to watch out for..

      Pros- great power gain and is identical to the BBK pulleys..pretty easy install Cons- the bolt that is provided needs to be shorter or a has to have a spacer... (the bolt as is will run out of threads leave the crank pulley only half pressed on).. by adding a washer it allows the bolt to pull in the pulley more.... Other thing is I have to switch to a smaller serpentine belt because my tensioner was maxed out and was causing the belt to slip...


      Year: 2007 Submodel: GT OC

      Helpful (10)

    • 5/5

      Installation Time: Afternoon

      February 27, 2012

      Horsepower Increase

      Awesome Product just as good BBK, without all the price. Just buy a new bolt instaed of cutting the one on your vehicle. Take your time, snap a picture of how your belt diagram, just in case.


      Year: 2008 Submodel: GT Agoura Hills, CA

      Helpful (6)

    • 5/5

      Installation Time: Afternoon

      February 23, 2012

      Pulley = Epic Win

      Hardest part about getting these installed was finding a friend with all the parts. It was a helluva lot of fun putting these on, the instructions were right on point. Note: this WILL require removing some hoses so you will want to be aware of some possible dripping. I'd have to say the car is a bit more peppy, I'm able to do wonderful things in 1st gear with no gas... Great fun!


      Year: 2008 Submodel: GT Austin, Tx

      Helpful (5)

    • 5/5

      Installation Time: Afternoon

      October 30, 2016

      SR Underdrive Pulleys added low end power

      I installed the pulleys in about 2 hours. The additional pull from 1500 to 3500 rpm was noticeable, higher rpm not as noticeable. Worth the cost and effort.


      Year: 2008 Submodel: Bullitt

      Helpful (3)

    • 4/5

      Installation Time: Shop Install

      Installation Cost: 0-$100

      September 26, 2013

      Smooths out performance a bit, but don't expect miracles

      I recently had these UD pulleys installed alongside a set of FRPP 3.73 gears. They seem to have offset the slight (1-2 mpg) drop expected by jumping from 3.31 to 3.73 rear end, and overall the car feels like it runs a little smoother. The engine feels as though it revs a little freer as well. Install cost for the pulleys was $75. A solid mod and I would buy them again.


      Year: 2007 Submodel: GT The Woodlands, TX

      Helpful (3)

    • 5/5

      Installation Time: Afternoon

      July 10, 2013

      AC on No Problem

      The pulleys are an excellent product! I decided to purchase the pulleys when I noticed a drop in power with the AC turned. It made the car feel a bit sluggish. The under drive pulleys restored the lost power lost with the AC turned on. Now I can enjoy the hot summer days in my mustang with the AC on and not feel the sluggishness when I want to put my foot into it. The pulleys look good and the construction of them is solid. The pulleys were easy to install with the instructions on American Muscle's website.


      Year: 2006 Submodel: GT Guymon, OK 73942, USA

      Helpful (3)

    • 5/5

      Installation Time: Afternoon

      March 08, 2012

      The best!

      I installed these on my 08 Shelby GT CS. It took about 2 hours and the results are amazing! They look great and install perfectly. I was so amazed at the horsepower, torque, and throttle response these achieved. If it wasn't for my racing lower control arms, it would be hard to keep traction on the road! I highly recommend!


      Year: 2008 Submodel: GT Longview, Texas

      Helpful (3)

    • 5/5

      Installation Time: Afternoon

      November 15, 2012


      pulling accessories causes a lag and robs horse power and man does this give it back, its not a bang for your buck its a hit, hit the gas and you will feel all the go for your doe. I love it. Troy


      Year: 2006 Submodel: GT roanoke rapids nc

      Helpful (2)

    • 5/5

      Installation Time: Less than 1 Hour

      June 29, 2012

      SR Performance Underdrive Pulleys (05-10 GT)

      This was a simple install about 1+ hours to do, It looks great and there is a very noticable HP gain.


      Year: 2008 Submodel: GT Selinsgrove, PA.

      Helpful (2)

    • 4/5

      Installation Time: Shop Install

      Installation Cost: $100-$250

      May 18, 2012

      Power when you want with fuel savings

      The stang definitely feels quicker on it's feet and the lighter pulleys help deliver better gas mileage when you're not gunning it. Best of both worlds. I got this installed at a shop, total labor cost $190 for a 2 hour job but it was worth it because they had to shave off a certain stud because one of the pulleys sits too deep. I think this is a great bang for your buck. With increased gas mileage, the pulley will pay for itself in about 2 years. Not bad.


      Year: 2005 Submodel: GT Fremont, CA

      Helpful (2)

    • 3/5

      October 10, 2016

      Worth the change?

      While the parts look good and the install was exactly as expected, the performance gain is very small. .03 of a second in the quarter isn't much of a gain. Just need to get more aggressive with my parts upgrades.


      Year: 2007 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      September 15, 2015

      Can't beat it for the price!

      I decide to go with the SR. because it was getting great reviews. I am happy I did, the fit was perfect and the gains were noticeable. I would recommend buying a new bolt ( m8 1.25 x 2" ) instead of cutting the factory one. I needed an impact gun because you can't get enough fast rotational torque with a breaker bar. It was a straight forward install just follow the guide. I would recommend these pulleys


      Year: 2007 Submodel: GT Palm Coast, Florida

      Helpful (1)

    • 5/5

      Installation Time: Full Day

      December 19, 2014


      The review title says it all these under drive pulleys are great I am very happy with this purchase they look great I prob could have had it done in an afternoon but I wasent in a rush and took my time making sure I had the pulley puller and followed all steps I did have an issue with the crank turning while in first gear and trying to remove the old crank pulley but it was an easy fix I just used a rubber adjustable filter wrench to hold the pulley in place so I could remove the bolt it took me about five mins to get the bolt out this way as my impact gun would not break it free


      Year: 2005 Submodel: GT Gainesville, GA, USA

      Helpful (1)

    • 5/5

      Installation Time: Shop Install

      October 11, 2013

      underdrive pulleys

      For the money you can't beat this product. Only problem was the motor would not stop turning. Had to wedge a piece of wood between pulleys to stop turning than it was a piece of cake. Looks great but not sure what I gained as I have not yet re-dynoed my car. 353 rwhp before install.


      Year: 2008 Submodel: GT Chatham, NJ, USA

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      June 19, 2013

      SR Underdrive Pulleys

      These are a great bang for your buck. They do make a noticeable difference in performance with no side effects, a/c is still ice cold, no overheating, etc. They also install easy in a few hours provided you use air tools. Just cut the stud on the alternator for clearance and get a new crank bolt from ford, its so cheap might as well. Overall I'm very satisfied with this mod. Also if you have an automatic like me, remove the flex plate cover and hold a bolt on it instead of on the torque converter.


      Year: 2006 Submodel: GT Fair Haven, NJ

      Helpful (1)

    • 5/5

      Installation Time: Less than 1 Hour

      May 08, 2012

      Perfect Pulleys

      I was a bit apprehensive going with the cheaper Stack Racing brand pulleys but couldn't be happier with this bolt on. Very easy installation that can be completed easily under an hour.


      Year: 2006 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Less than 1 Hour

      February 29, 2012

      eye candy

      made the engine look better, a slight notice in power and only took about 1/2 hour to install.


      Year: 2006 Submodel: GT zanesville, ohio

      Helpful (1)

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