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SR Performance Underdrive Pulleys (05-10 GT)

Item 41131
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      Review & Installation Video

      Hey, guys. It's Joe from AmericanMuscle. And today, we're gonna be taking a closer look at the SR Performance Underdrive Pulleys, fitting all '05 to '10 GTs. This is gonna be a great option for the bolt-on three-valve owner out there that's at the end of their build list and they're looking to get every last bit of horsepower out of their 4.6.So what do we have going on here with the SR Performance underdrive pulleys? We'll over here we have a brand new crank pulley that is going to be smaller in diameter than the factory one and over here we have our new water pump pulley that's gonna be a little bit bigger in diameter than the factory one. In the middle here we have a brand new bolt for the crank pulley.Now in order for us to understand what these bad boys are gonna do for your Mustang, we have to understand basically how these work first and how these are going to improve off of factory. Now pulleys in general, they're there to power the accessories on your motor, that's gonna be stuff such as your water pump, your alternator, your AC condenser, and they're going to cost a small amount of horsepower in order to do so, otherwise known as parasitic drag. This is why you at least typically don't see AC on Formula 1 cars because it would cost a little bit of extra horsepower to run it.Now nobody wants to lose their AC just to gain 15 horsepower, that wouldn't make sense unless you're really, really in the track days. But with something like this, by downsizing our crank pulley a little bit and upping the size of our water pump pulley, we can lessen that parasitic drag by basically underdriving the accessories on our motor. This isn't going to be a huge horsepower gain, but like I said earlier if you have all the bolt-ons done in your three-valve, you're looking for something to do to net just to add that little bit extra, this is gonna be a great pickup. Definitely a great supporting mod end of the build type of stuff here but a great mod none the less.Now another huge benefit of these is they're also made out of a lightweight aluminum, so that's going to lessen a little bit of rotating mass and if you're doing any track days, that's exactly what you want. It's not gonna be a huge amount like an aluminum flywheel or lightweight driveshaft would give you but less rotating mass is always a good thing. This is gonna help your motor spin up to redline as fast as possible. Again, not a huge game but something that consider. These are also SFI-certified and there's no tune required n order to get the gains that something like this would give you.Pricing is gonna drop in right around 160 bucks and that's really not a bad price to pay when it comes to netting some free horsepower that was there to begin with, it's just reclaiming it back from those accessories. So this is definitely a good pick up again if you're at the end of your build. The install here, albeit, this is not your regular old cold air intake, something that easy, this is gonna be a little bit tougher than that, but not too bad, you could definitely accomplish this in a couple of hours in the driveway if you come with the right tools. I'm gonna give it a two out of three wrenches on our difficulty meter. I think you can get this done in about two to three hours if you take a look at this video and come with all the right knowledge. So without any further ado, let me show you what tools you'll need and then how it's done.Tools required for this install are going to include a breaker bar, cut-off wheel, die grinder, flathead, safety glasses, pulley removal tool, RTV, torque wrench, 18, 10 and 8-millimeter sockets, an impact and ratchets. So we're gonna start with some disassembly in our engine bay coolant reservoir, that's gonna have to get disconnected. Power steering reservoir, that's gonna have to go, also our intake tube here, that is going to be the easiest part that's going to have to go as well. To loosen that up the clamps are an 8-millimeter socket and we're gonna start right there.We're gonna start by disconnecting our breather hose and that is just gonna be this green tab on the bottom. If you push down and pull over on that, that will loosen up like so. Then we can come in with the old ratchet here and loosen up the clamp on our throttle body. Again, 8-millimeter socket. Over here by the airbox we have one more clamp, again, 8 millimeters. And then we can pull this whole thing off just like so.Next up our coolant reservoir, two 8-millimeter bolts to loosen that up. Hold onto those because you are gonna need them later obviously. Then we can just pull this up, remove that hose and put it over to your by the airbox. Power steering reservoir, that is another 8-millimeter bolt. And again hold onto that, then we can pull that up off of our fan and that can just kind of float there for now. I'm just gonna tuck it up by the airbox a little bit, try to hold that in place right there.Next up we have to get rid of this fan shroud and fan assembly but we have to disconnect it first, this plug right here, there's a release tab over on this side. However, if it's never been apart on your three-valve before can require the use of a screwdriver. There are two bolts that hold the fan on at the top, one on each side, again both 8 millimeters then you can pull the fan assembly out.Here we have a clear shot at our water pump pulley and while the belt is still installed, we're gonna use that to hold it still while we crank the four bolts loose. And these are 10 millimeters by the way. We're gonna loosen up our crank pulley while we're down here as well. This is an 18-millimeter socket. Now we can get rid of the belt and in order to do that, half-inch drive breaker bar and then off the top. With that out of the way, I'm just going to get rid of the rest of the 10s on our water pump pulley and that is uninstalled.Removing the crank pulley however is not as simple. You're gonna need to find one of these pulley remover tools whether you buy one from Harbor Freight, rent one from Pep Boys or AutoZone, pick one of these up because you are gonna need it to get this guy off, the tension is just too much. You could see the one we have here, it just has that lip that goes around this lip on the pulley and then we can use a socket to basically press against a bolt we have installed into our crankshaft and this pulley is going to come with us when we turn this socket. And obviously these arms here can be a little bit of a pain to set up, so I went ahead and did that off-camera. And I'm just gonna remove the bolt I used as a standoff and we can pull out our pulley.So now that we have everything off of our Mustang, now is the perfect time to stop down, put these two sets of pulleys on the table next to each other and highlight some key differences between these two. The biggest difference is going to be the sizing. Over here, you see our two crank pulleys, the stock one is gonna be bigger, the aftermarket one is gonna be a little bit smaller. Now these are going to be considered driving pulleys so our engine is spinning at the same speed. One rotation of this is going to spin more of the belt because it's bigger in diameter than one rotation of this which is going to be spinning the belt a smaller amount because it's smaller in diameter, less distance for the belt to go one rotation all the way around this thing. So the difference here, bigger is going to be faster, smaller is gonna be a little bit slower. And again that's there to reduce parasitic drag.Now weight is also a difference between these two, like I mentioned earlier, this is aluminum, this is cast iron. The weight difference is small. Like I said, it is rotating math, so every little bit of weight you can shave off is good. Next, we can and talk about our water pump pulleys and these are going to be a little bit different. The pulleys over here, our crank pulleys, these are driving the belt while our water pump pulleys, these are being driven by the belts. So these are gonna be similar to a supercharger. The smaller you go on these, the faster it is going to spin the water pump and same thing goes for all the other driven accessories. So this is our stock one over here, the bigger you go the slower this is going to spin. And if I go like this you can just see how much bigger that that aftermarket water pump pulley is gonna be. Same thing over here we have aluminum and this is going to be a drastic difference in terms of weight. The aluminum is a lot lighter than the factory stuff when it comes to the water pump pulley. So that pretty much sums up the differences between these two. There's one thing we have to take care of before we move on and install our new crank pulley and that is RTV. We're gonna have to apply a little bead of this into the keyway to make sure everything seals up correctly and no oil escape from that keyway.So now we can do our install. We're gonna start with the crank pulley, we're just gonna line up the keyway. That actually pushed right into place, a lot of times that will put up a little bit of a fight. That longer bolt in the kit is included so that if this does fight, you could throw a washer on there and use that to sort of pull this into this position and then you can install the factory bolt. Ours slid right on so we're just gonna install the factory bolt.We're gonna wait to torque down our crank pulley until the belt is on, hopefully that gives us a little bit of friction to fight against to tighten that down all the way. We want to make sure we hit our torque spec with that one. But with that said, we're gonna move on to our water pump pulley and while it looked easy coming off, going on is a little bit tougher. You can see the cut-off wheel in my hand here, reason being there's a stud in the way that's gonna have to go to make room for the larger water pump pulley. So we're gonna cut that off, clean up the stud a little bit, and then our water pump pulley should go right back on. Safety glasses for this one guys. This guy has got to go, just barely not enough clearance for our water pump pulley. That looks good, so we're gonna clean that up and install our pulley. So now we can put on our water pump pulley and we're just gonna secure that with the factory 10-millimeter bolts. Now that we have all of our pulleys applied, we're just gonna loop in our belt.So before we put our Mustang back together, we still have to torque down that crank bolt, there's a little bit of a process to that. First thing's first, you're gonna need a torque wrench because the first thing you're gonna need to do is torque that bolt to 66 foot-pounds. Now once you hit that 66, we're gonna lose in a full 360 degrees and then you can torque it to 37 foot-pounds and then you add another 90 degrees quarter turn just to make sure it's seated properly, you're gonna need an 18-millimeter socket to do so. So our first torque spec, that's gonna be 66 foot-pounds. Hopefully, these don't spin. Right on the edge of it spinning. Then we can come off the full turn. Then we can lower the torque wrench to 37 and then we're gonna give that one more quarter turn just to make sure that's tight and this is exactly how Ford recommends you tighten this down.Then we can start to rebuild by dropping back in our fan and we can secure that with the two 8-millimeter bolts, one in each corner. Don't forget to plug this back in as well. Now after that, we can secure our power steering tank to the fan shroud. Again, this is an 8-millimeter bolt. And we could do the same exact thing for our coolant reservoir as well.Last but certainly not least, we have to do our intake tube that's gonna go around the airbox and the throttle body. We can tighten down the clamps with an 8-millimeter socket but also we're gonna click in this breather hose as well. Guys, that is gonna do it for the SR Performance Underdrive Pulleys, fitting all '05 to '10 three-valve GTs. As always, thank you guys so much for watching. Subscribe for more like this one. Keep it right here at AmericanMuscle for all things Mustang.

      Product Information

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


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


      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.

      SR Performance

      Fitment: 2005 2006 2007 2008 2009 2010

      MPN# 41131

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (100+)

      Write a Review

      Ratings Summary

      4.6 out of 5 overall rating from 100+ customers

      Installation Time: Afternoon

      Installation Cost: $100-$250

      • March 25, 2020

        5 2005 GT - TeresaK

        underdrive pulleys

        underdrive pulleys went on easy, perfect fit!! Love them

        Helpful (0)
      • February 26, 2020

        5 2010 GT - mezakun Installation Time: Afternoon


        The under drive pulleys where really easy to install nothing to hard especially when they have a video step by step I did feel the engine work a lot more smoother then before , feels somewhat more quicker off the line

        Helpful (0)
      • February 23, 2020

        1 2009 GT - MikeL Installation Time: Afternoon

        Falling apart after 5 months of use

        I bought this. Seemed great at first but after about 5 months I noticed the pulley bolts seem weird and sure enough they are loose and nearly falling apart. Driving it anymore would have severely damaged my engine.

        Helpful (1)
      • January 23, 2020

        1 2006 GT - Pulleys Installation Time: Less than 1 Hour

        Underdrive pulleys

        They made my vehicle over heated on the first day check the pulleys everything was put correct right wasted money down the drain I don’t recommend these only a idiot like me will buy them

        Helpful (0)
      • January 07, 2020

        5 2007 GT - Oldscotian Installation Time: Afternoon

        Helpful (0)
      • December 27, 2019

        5 2007 GT - JeremyB Installation Time: Afternoon

        Very noticeable increase in throttle response!

        A great and inexpensive mod! Installation can be a headache if you don't have the proper tools, but it is still possible with regular hand tools! It took me some doing to remove the stock harmonic balancer but once that bolt was broken the rest of the installation is simple!

        Helpful (0)
      • December 14, 2019

        5 2010 GT - Uriel Installation Time: Less than 1 Hour

        Love it

        Dude not gonna lie after I installed them and test drove it. I could instantly feel the difference before the pulleys it would feel sluggish now it feels like I get instant power as soon as I accelerate I love them

        Helpful (0)
      • November 30, 2019

        5 2007 GT - GT Installation Time: Less than 1 Hour


        The SR PERFORMANCE underdrive pulley kit was an awesome performance upgrade for my 07 GT what a difference in power gains and throttle response easy install and well worth the money

        Helpful (0)
      • November 07, 2019

        4 2006 GT - Aguitas Installation Time: Weekend


        I save more gas in my car the engine feels smooter fasther

        Helpful (2)
      • October 20, 2019

        5 2010 GT - Maadpny Installation Time: Afternoon

        I can feel the difference

        At first i was a little skeptical but after installing these pulleys at the shop i felt a big difference specially the throttle response.

        Helpful (0)

      Questions & Answers (39 answers)

      5 Top Rated Questions

      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.....

      Helpful (13) Show 2 more answers

      Does this require a tune?

      • The SR Performance Underdrive Pulleys do not require a computer tune.

      Helpful (8)

      Will the belt remain the same or does the belt have to be shorter or longer?

      • These pulleys allow you to reuse your factory belt.

      Helpful (4)

      Will this work on my 07 roush 427R supercharged Mustang?

      • These pulleys are compatible with the 2007 Roush 427R and will work with your Mustang.

      Helpful (4)

      Will these give more power over the BBK or Steeda udp's?

      • They will all be right around the same.

      Helpful (2)
      10 More Questions
      I'm trying to install this product but the bolt for the crank shaft is not fully going in why is that? 1 answer
      There's is a slight bend on my underdrive pulley. Like very very small on the lip. Is that going to effect anything to still use it? 1 answer
      Would this replace the stock pulley on a 2008 Crown Vic 4.6? 1 answer
      What kind of horsepower gain can you expect with these pulleys 1 answer
      Can this install require a new tune update and will that add any additional gains? Compared to just an install without a retune? 1 answer
      is this considered a non piggyback ? 1 answer
      I've had mine in a box for about 2 yrs now. My concerns relative to mostly what I've read online. I'm 52 yrs young, so aftermarket isn't anything new to me. My situation is, our 09GT 5spd is a daily driver for my wife, thankfully she works 2 miles away from home. However, with the changes, both Pro and Con, these pulleys make I see/read the effects with the alternator, but whats the deal with the A/C? We live in FL. so anyone married knows what life is like without A/C in the wife's car. 1 answer
      If my car is tuned, will I have to get it tuned again when I install the pulleys? 1 answer
      can i use this for the Mustang 2006 V6?? 1 answer
      What accessory does this replace? Does it replace the a/c? 1 answer

      Installation & What's in the Box

      Installation Info

      What's in the Box

      • (1) Crank Pulley
      • (1) Water Pump Pulley
      • (1) Crank Bolt
      • (1) Instruction Sheet

      Tech Specs

      Underdrive Pulley Specifications
      Year/Model:2005-2010 GTManufacturer:SR Performance
      Crank Pulley: One Piece Crank SFI Certified:Yes

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