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Kooks Header and Off-Road X-Pipe Combo - 1-3/4 in. (11-14 GT500)

Item 65525
AmericanMuscle no longer carries the Kooks Header and Off-Road X-Pipe Combo - 1-3/4 in. (11-14 GT500). Please check out 2015-2023 Mustang Headers for an updated selection.
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    Video Review & Installation

    Justin: The Kooks 1-3/4-inch-long tube header and off-road X-pipe combination will be an excellent way for Shelby owners to really uncork that exhaust system and get more power and a lot more sound out of your '11 to '14 5.4 or 5.8 GT500. Now, the Kooks setup will combine their killer craftsmanship with the quality 304 grade stainless steel for just north of the $1500 price point, and can be used either with a factory cat-back, a corresponding Kooks cat-back, or other aftermarket systems that do utilize that factory style connection. Now, installing the Kooks long tubes will not be for everyone and therefore will get a knuckle-busting three out of three wrenches on the difficulty meter with a detailed walkthrough to come later in the video. Let's break down these components a little bit further. And right up front, guys, I'm going to tell you, you're looking at top-notch quality 304 grade stainless steel throughout here with these headers including the 1-3/4 inch primaries which we will talk more about in a minute, the 3/8 inch laser cut flange at the head, and finally all exiting out the 3-inch collector here loaded with Kooks' merge spike technology. And the idea behind that, guys, is to increase the exhaust velocity but also the scavenging as well. That's two big things you're looking to achieve when improving the exhaust system on any car, including your Shelby. But going back to that 1-3/4 inch primary size we just mentioned here, and that will actually be the minority on the site in regards to the 5.4 and 5.8 cars, whereas, the most common size will no doubt be the slightly larger 1- 7/8 inch header. Now, both options, in my opinion, are going to make great power over those factory manifolds that you will be replacing. But conventional hot rodding wisdom might tell you that the smaller diameter here will make a little bit better torque in the lower RPM range, but might become more of a restriction up in the upper RPM level and vice versa. And what I can tell you is the difference is going to be very minimal at best, guys. Don't overthink this too much. But nevertheless, it's not a bad idea to do some homework on the topic before pulling the trigger on a particular header. But aside from the headers themselves, Kooks does also include their off-road X-pipe with this particular package here and the same killer quality we saw with the long tubes does carry over to the X-pipe itself. And what does that mean to you guys? Well, full 304 grade stainless throughout here as well, including the 3-inch mandrel bent tubing and the catless design, which again, will deliver the biggest power and sound gains compared to a catted option but won't be emissions-friendly in every state. So, never a bad idea to check your local laws first before installing.Kooks does also toss in brand new gaskets along with all of the necessary hardware and O2 extenders to get everything in place. Now, before we get into the installation, I do want to point out that we strongly recommend pairing up your new Kooks setup here with the use of a custom tune. Now not only will that get you a little bit more power out of your setup and eliminate the check engine light caused by removing your cats, but it's also because the headers are going to move your primary O2 sensors a little further downstream, and that might cause your car to run a little bit rich without touching the calibration. So again, this is totally your call but something I would recommend thinking about before pulling the trigger on this particular product. All right. Now, let's talk about the installation, and again, a fair amount of work here, guys, a fair amount of knuckle busting and your favorite four letter word. So, let's go three out of three wrenches on the difficulty meter and at least a day or two in the shop or garage depending on your setup and how fast you like to work. And to give you a better idea of what's involved with this rather extensive install, here is a detailed walkthrough along with the tool breakdown. Man: First thing we're gonna do is remove both battery cables followed by the battery and the battery tray. You're gonna need an 8-millimeter socket to do this. All right. We can lift our battery out now. Don't forget to release the push pin that holds the positive battery cable to the battery tray. Once you've got that out, then you can pull your tray out, along with the strap. Next, we're going to remove our air box assembly. First we're going to loosen the clamp up at the throttle body. Next, will remove one of our PCV lines right here and our mass air flow sensor plug and one vacuum line on the right side. And we should be able to lift this entire thing out in one piece. Next, I have a 15-millimeter socket, I'm going to remove this K-member support brace right here. Next, with a 15-millimeter socket, we are going to remove our H-pipe. I'm gonna start with the two nuts up at the flange where the H-pipe meets the manifolds. Next, we can unplug the two O2 sensors. Now, I've already unplugged the front O2 sensors. They are buried and you cannot see them. Next, we're going to loosen the clamps up at the over axle pipes. This is also a 15-millimeter. We can now remove our stock H-pipe.Next, we can remove the two wires on the back of the starter, and from there, we can then remove the starter. I have a 10-millimeter socket for the small wire and a 13-millimeter socket for the larger wire. Next, using a 10-millimeter socket, we can remove the three bolts holding the starter in place. Next thing we're going to do is remove our steering shaft. A good tip here is to mark your steering shaft with a Sharpie, so you can put it back together the exact same way it came apart. We're now going to remove the 13-millimeter bolt holding the steering shaft into the knuckle. Now, this should telescope out and we should be able to remove it. And that's out of the way. Now we can tuck that up out of the way. I'm gonna stick my bolt back in here so I don't lose it. All right. Next, we're going to take a 13-millimeter socket and remove the two motor mounts. I have supported the engine and transmission with a pole jack right here. All right. We're now ready to remove our right side motor mount. All right. We're gonna start removing the manifold bolts now. They are 13-millimeter studs. Some of the nuts will come off and some of the studs will come all the way out of the heads. All right. We're still going through here removing manifold bolts. I have a 13-millimeter socket on my ratchet still. A lot of these you cannot even see. We might be able to get to some of them from up top, some of them from down below. We are now ready to install our new long tube. All right. Now, we can start to tighten up some of our manifold bolts here. So, in order to get our motor mounts back in, I'm going to pull the oil filter here. It's going to give us a little bit more room to work. All right. We're now ready to put our left side motor mount back into place. Let's see if we can get this thing fished in here. We're still tightening up our motor mount bolts here. Next thing we're going to do is reconnect the knuckle and the steering shaft. Put our oil filter back into place now. Be sure to check your oil when you're all said and done if you lost any when you pulled your oil filter out. All right. We can put our right side motor mount into place now. It should be a little bit easier than the left side was. All right. I'm gonna put the starter back into place now.All right. We're now ready to swap over our O2 sensors. I have a 7/8 wrench here for this. All right. Now, we can plug this in, and we will zip tie this up out of place. All right. And we can now plug in our O2 sensor, click, and zip tie it up. Next, what I'm gonna do is install our X-pipe. So, first I'm going to try and get it on our over axle pipes, slid in here. All right. From there, we can get these pipes started. All right. We can use the supplied hardware to get these two bolts started. We are now going to put our rear O2 sensors into place. We're now ready to put our K-member support brace back up into place and we'll tighten these up with a 15-millimeter socket. We're going to put our battery tray back into place now. And next comes our battery. Battery cables are next. Get these tightened down. Last but not least, we're gonna throw our air box back into place here. All right. And we can plug our mass air meter back in right here, one PCV line right here, and we've got one little vacuum line on the side over here. All right. We'll just tighten up our clamp here at the throttle body. Justin: So, wrapping this one up, if you have an '11 to '14 Shelby GT500 and you want a very high-quality long tube header and an off-road setup, the Kooks certainly is worth a look. And you can find out more about this product right here at

    Product Information

    Features, Description, Q&A, Specs & Installation


    • Increase Rear Wheel Horsepower and Torque
    • Includes Long Tube Headers w/ Matching Off-Road X-Pipe
    • 304 Stainless Steel Construction
    • For Off-Road, Track Use
    • Free Flowing Mandrel-Bent Tubing
    • Fits 2011-2014 Shelby GT500 Mustangs


    Improve Horsepower And Torque. The Kooks Long Tube Header and Off-road Shorty X-pipe combo kit for the Shelby GT500 Mustang will balance out the exhaust pressure to increase flow over the restrictive factory exhaust system resulting in more horsepower, torque, and better throttle response.

    Quality Construction.
    Manufactured from 1-3/4" mandrel bent 304 stainless steel tubing Kooks Long Tube Headers are TIG welded for strength, and feature a leak-free ball flange design to fit perfectly into the included 3" diameter 304 stainless steel Shorty X-pipe for excellent exhaust flow and performance.

    Natural Finish. These Kooks Headers feature a natural stainless steel finish, which provides an aggressive appearance to your engine bay. This is not a heat-resistant coating, AmericanMuscle recommends the use of Exhaust Heat Wrap for high performance applications.

    Recommended Upgrade. To realize the full power potential that this Kooks Long Tube Header and X-pipe Kit has to offer, AmericanMuscle recommends a Bama custom tune with a Mustang Handheld Tuner to reprogram the vehicles computer (ECU) for proper operation.

    Application. This Kooks Long Tube Header and matching off-road shorty X-pipe combo kit is designed specifically for the 2011 to 2014 Shelby GT500 Mustangs.

    Technical notes. Not legal for use on pollution controlled motor vehicles; intended for off road use only.

    CA Residents: WARNING: Cancer and Reproductive Harm -

    Installation & What's in the Box

    Installation Info

    What's in the Box

    • (1) Driver side header
    • (1) Passenger side header
    • (2) Gaskets
    • (16) Small bolts
    • (8) Flat washers
    • (4) Long bolts
    • (4) Nuts
    • (1) X-pipe
    • (2) Down pipes
    • (2) Clamps

    Tech Specs

    Header Specifications
    Header Type:Long Tube Finish :304 Stainless steel
    Type Mid Pipe Required:Kooks Shorty XFitment:2011-2014 Shelby GT500

    Mid Pipe Specifications
    Style Mid Pipe: Shorty "X"Type Headers Required:Kooks Long Tube
    Piping Material:304 Stainless SteelPiping Size:3"
    Catalytic Converter:"NO" - For off-road use onlyFitment:2011-2014 Shelby GT500

    Questions & Answers

    10 More Questions

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