Project Silver Bullet is one of the newest test beds in the StangTV stable, and so far we’ve been able to hook up the machine with a stout supercharger system from the team at ROUSH Performance, solidifying the engine’s performance and getting the project underway. But no project car is complete without a stout exhaust system, so to that end we enlisted the help of the team at Kooks Headers And Exhaust, getting the Silver Bullet’s factory pipes out of the way and installing the company’s long tube headers, Green Ultra High Performance Catted X-pipe and over-axle tubes to complement our ROUSH Performance axle-back system.
Ever since 1962, Kooks has been crafting headers for many different vehicles. From drag racing terrors to offshore boats, their products have been under the hood of all sorts of champions all over the globe. They have dozens of applications in their catalog, and sometimes even more than one fitment per application, as in our instance.
The 2013 Mustang GT arrives at the dealership with a set of 1 3/4-inch short-tube “headers” that look more like an engineer was trying to figure out what to do with the scrap metal laying around the factory. Of course, the OEM application needs to take a multitude of things into account, such as noise, vibration and harshness, emissions compliance, assembly-line fitment, and more.
That’s where the team at Kooks comes in – their headers don’t need to have the same sorts of compromises in terms of fitment, as the end customer is looking for more performance for their machine, rather than worrying about whether the exhaust will be easy to install in under ten minutes on the assembly line.
For the 2011-14 GT/BOSS 302 Mustangs, Kooks offers two different header assemblies – a 1 3/4-inch long tube design [PN 60-41-175], and a 1 7/8-inch design [PN 60-41-188]. Both sizes can be had for around $1,000 depending on your vendor of choice and offer a number of features that make them standouts in the marketplace. They’ve also recently released a set of headers with massive 2-inch primary pipes [PN 60-41-200] for the ultimate in power production for those running huge superchargers and looking for every last ounce of exhaust scavenging. They even offer a 1 7/8-inch Super Street Series short-tube header [PN 164100] for connecting to the factory mid-pipe.
For our application, the Kooks team sent us a set of the 1 7/8-inch long-tubes, which come complete with 3-inch merge collectors, oxygen sensor bungs, and all emissions components pre-installed at the Kooks factory in North Carolina. In addition they sent us a set of rear pipes that flow all the way to the ROUSH Performance axle-back that we previously installed. These tubes have no resonators like the factory pipes – they are a straight-through design. The 1 7/8-inch primary size will maximize exhaust flow in our ROUSH-blown machine and add plenty of power and torque as you’ll see later on in the article.
All of the products in the Kooks catalog are crafted from T304 stainless steel, which assures a long life under the hood. All of the hardware needed for installation including a set of high-temp gaskets, nuts, and bolts is also included.
The headers feature a set of computer-designed tubes, made with a BASIS 3D Arm imaging machine that helps the Kooks team to maximize the space available under the hood. Instead of a traditional header where all of the tubes sweep downward from the cylinder head, for space reasons these puppies have two tubes on the passenger side that are routed topside before going down to the collector, and one on the driver’s side. This design provides a unique look when the hood is up without sacrificing performance or spark-plug accessibility.
“The BASIS Arm allows the guys to plot out the engine bay and design the tubes from there. The flange is placed on the head, along with the installation of a spark plug, and then the machine tells us where we can place the tubes,” says Kooks’ Drew Amitrano.
We feel that the car will make 40-45 horsepower at the crank once you get the boost back to where it was. -Drew Amitrano, Kooks Headers
One of the caveats to using the Kooks header system on a 5.0L Coyote engine the need to use one of Kooks’ X [PN 60-42-ORX or 60-42-CATX for the standard converter-equipped version] or H-pipes [PN 60-42-ORH or 60-42-CATH] to go with the system. They even offer two different versions that are built to accept the BOSS 302’s factory side-pipes [PN 60-42-CATH-302BOSS and PN 60-42-ORH-302BOSS]. Add -G to any of the catted part numbers to get your pipes with the ultra-high-performance Green catalytic converters.
While the addition of the mid-pipe does provide a bit of added expense at the outset of the project, it’s well worth it in terms of performance, sound, and appearance. The factory mid-pipes are a unique 2.75-inch diameter, and that just won’t match up well with the 3-inch collector on the headers. Each of the Kooks X and H-pipe versions does neck down to 2.75-inch at the axle-back side, as nearly all of the axle-back exhaust systems on the market use this factory dimension. As the neck-down section is far from the header outlet, the drop in performance is negligible. Additionally, there is a distinct difference in tone between the two merge pipe styles, and each consumer likely has their own preference – we’ve got video of what ours sounds like down below.
Since our GT resides in the enthusiast hell hole called the state of California, we opted to use the Kooks Green Ultra High Performance catalytic converter design for Silver Bullet – we used PN 60-42-CATX-G in our application. Amitrano explained, “The Green UHP converters offer a less-restrictive, 4-inch body, 300-cell converter that is 49 state certified by the EPA and help to reduce emissions. They will work on vehicles producing up to 800 horsepower and have been designed to have a super high-flow pass-through level, meaning that they won’t create engine codes in most vehicles, preventing the dreaded check-engine light from illuminating.” The converters can handle exhaust temperatures up to a whopping 1500 degrees Fahrenheit without melting, and are ideal for just about any street-going horsepower-making machine like the Silver Bullet.
While no headers are “easy” to install, these weren’t nearly as difficult as we anticipated. Removal of the factory pipes was relatively straightforward – we pulled out everything except the previously-installed ROUSH Performance axle back. Pulling out the starter is a must, as is disconnecting the steering shaft.
We also found that removal of the engine mount on the driver’s side made the process much simpler, but you need to take into account that we were working in the fully-equipped Power Automedia shop – a place that’s got all of the tools, engine jacks, and everything else we needed to make this an easy process. After the removal of those items, getting the factory “headers” out became a breeze. Installation is the reverse of removal, and since the Kooks headers have slots instead of bolt holes on the mounting flanges, we were able to hang the gaskets and pre-start a few of the bolts into the head, making the installation process a step-by-step exercise in following the Kooks instructions. Follow along with the photos for more details.
On the dyno, we got the results we were expecting. While the headers did not pick up a huge amount of horsepower, the reduction in back pressure from the restrictive factory pipes to the Kooks free-flowing pieces dropped our boost level. We picked up 12.1 hp and 13.4 ft-lbs of torque with decent gains across the entire RPM range. This brings our peak power numbers to 502.2 hp and 451.5 ft-lbs. With the reduction in boost, we’re not working the engine as hard, yet making more power. And the sound difference is nothing short of astounding – check out the video for a taste of Kooks-equipped, quad-cam Coyote goodness.
With a smaller pulley swapped out on our ROUSHcharger, we were able to get back to our 8.5 psi boost level. With that, we picked up an additional 18.5 hp and 27.7 ft-lbs to the rear wheels. Our total gains put us at 30.6 hp and 41.1 ft-lbs with the Kooks long tubes, catted X-pipe and over-axle pipes, putting us right in line with Amitrano’s 40 horsepower to the crank estimate.
“If it lost that much boost and still made power, it’s making a ton of power. We feel that the car will make 40-45 horsepower at the crank once you get the boost back to where it was,” says Amitrano. And it’ll do this while retaining the catalytic converters – a good thing for our California car.
On a naturally aspirated Coyote, solid 25-30 rwhp gains should be completely realistic. For you folks with power adders like ours, expect a boost drop with the lack of back pressure, though it’s very easy to get levels back up where they were and take full advantage of the power gains from the full exhaust upgrade.We found the modifications to be well worth the time and expense, so if you’re in the market for hopping up your Coyote-powered machine’s performance, you owe it to yourself to give Kooks Headers and Exhaust a call.