So there are plenty of companies out there who tout that their bolt on products can generate a lot of power. But often the reality is that those power gains come at a price with additional modifications required or drivability sacrificed to get to the goal line. In our testing, we were very pleased to discover that the installation of our Kooks complete exhaust system, which included their “Ultra High performance Green Catalytic Converters,” generated as much as 55 horsepower before tuning. For those who are new to the bolt on game, that is quite a lot.
The Kooks system includes their very shapely exhaust header design that is a one-piece unit in contrast to some header packages that feature individual header tubes that are slipped together to form a complete header. In this case, the header (the section of tubing that bolts to the cylinder head and forms a flange to connect to the rest of the exhaust system) is made from high quality 304 stainless steel in its entirety. For that reason, it will not rust with age and is guaranteed for life. We can tell you, from a visit to their facility in Statesville, North Carolina, that these headers fit because great care has been taken to make each piece exactly to specification.
The design of the header is key to releasing the hidden horsepower found in our Coyote engine. Our 2018 Mustang was slightly different from previous S550 Mustangs (2015 -17) but much of what we experienced here is pertinent to those earlier models and the 2019 model year as well. For anyone who has dealt with header design, the key to creating more engine power is more than just increasing the side of the tubing diameter over the stock header package. Our factory Mustang exhaust was not bad in comparison to many other factory muscle car systems, but it was hampered in some areas because the factory narrowed down the tubing to clear engine bay components. In addition, the Kooks’ scavenger collector design is responsible for significant flow enhancement as is the collector spike (visible when looking into the collector) that adds in airflow efficiency.
The complete kit also includes the rest of the 304-stainless steel tubing, mufflers, catalytic converters, clamps and exhaust tips to dress out the system in the most efficient way. The proper installation of the mid-tubes and other component was laid out clearly in the nicely detailed Kooks instructions, but just know that once the headers are in, the rest of the installation is very easy.
And so on to the headers . . .
So lets cut to the chase, our Kooks complete exhaust system generated as much as 55 additional horsepower at 3400 rpm before tuning using the Kook exhaust system and “Ultra High Performance Green Catalytic” converters. That is huge power for a bolt on. Note that we did not call it simple – and that’s for good reason.
For those who tout themselves as a decently adept mechanic, your skills could be highly tested when installing the header portion of this exhaust. Among the challenges we encountered during our installation were jacking up the engine and removing both engine motor mounts. Other vehicle components that are dislodged in this process include the battery, air intake system, steering link and starter, and that’s just to be able to remove the factory exhaust headers.
In the end, as our dyno proved, the peak Rear Wheel Horsepower (RWHP) improved from 415.22 RWHP to 440.46 RWHP and Rear Wheel Torque improved from 392.97 lb. ft. of torque to 416.57 lb. ft. What was most incredible were the performance gains in the mid range, an incredible 55.05 RWHP at 3400rpm – right in the sweet spot where you are going to feel it the most when accelerating. While not everyone can take advantage of this upgrade (several states including California do NOT allow the installation of long tube headers on late model Mustangs – check with your local regulations before making this swap) those that can will find the benefits to be very impressive.
Best of all, as performance fans have known for years, installing a set of headers is the first step on the list performance upgrades that allows you to garner the most from additional upgrades like superchargers and intake systems. To install a power adder without opening up the exhaust with a header system for improved engine efficiency is not getting all the power they deserve.
And don’t you deserve all that power?
These are the parts we installed out our 2018 Mustang. While the headers were a battle to install requiring us to remove the motor mounts and lift the engine side to side to install the headers, the rest of the system was a snap by comparison.
Our first step was to unhook the battery, remove it and then remove the battery box in its entirety.
From here we did a lot of unhooking of the systems that were in our way in our quest for the factory exhaust system. Here we unhooked the MAF sensor from the air intake. Tagging these plugs is a good idea and taking a few photos with your cell phone as you do this will help when reinstalling the factory harness system.
The engine cover is released by removing the circular fastener covers and removing the two nuts that hold it in place. The back of the cover snaps in place – or unsnaps in this case.
We removed the air intake box in two sections. First take off the top and then unbolt the lower. It’s much easier to do it this way rather than pulling it out as one piece.
Here is a first look at the factory Ford exhaust headers that will be removed shortly. From this angle, working on the passenger side of the engine first, we released this nut on the motor mount. The entire motor mount has to be removed but that happens from below the car.
From under the car, we unbolted the factory header at the collector from the factory catalytic converter.
Under the car, this bracket holds the clips that connect to the rear oxygen sensors. We unclipped them both and let the wires hang down.
The oxygen sensors were unscrewed from their mounts in the factory exhaust and labeled as to which side of the car they came from. When we install the new Kooks system, we will make sure they stay on the same side of the car.
To prep for the future Kooks component installation, we began by removing some of the factory parts starting with the mid-pipes and resonators.
It is common for some of the original parts to stick in place requiring some additional persuasion to release from their mount. This dead blow hammer is a great tool for this and avoids damaging factory clamps and tubing in case they need to be reinstalled at a later date.
The rear exhaust section is held in by this series of hangers. By unbolting the two bolts that hold the teardrop-shaped black brackets from the crossmember and the rear hangers by the mufflers and tips, most of the exhaust is released.
Case in point is how we dropped the system in one piece once it was disconnected at the mid-pipe. Note that the rear brackets are unbolted from the frame rather than attempting to slide the hanger rods out of the rubber isolators.
If this is your first time doing a project like this, you will learn that access to each of the exhaust header studs comes at different times in the procedure. When a stud becomes accessible, such as this one, you remove the nut. Note the hex on the end of the stud. For this installation, new Kooks header bolts and retainers will be used so the studs will have to be removed as well.
As mentioned earlier, the starter is also removed to gain enough room to slide the header up once the factory exhaust is out. Remove the electrical connections and keep note of how they went on for easy reinstallation.
This series of lines attaches to a bracket that is located by the bolts that hold the motor mount in place. We were able to unbolt the bracket and move it out of way enough to avoid having to break the lines free and make the entire process that much more challenging. Do not, however, kink any of these lines when you make this maneuver.
Carefully support then lift the engine to take the pressure off the motor mount on the passenger side. We placed the jack on a pad in the corner of the block. Do not lift the engine by the transmission bellhousing.
The motor mount is held in place with three bolts. After lifting the engine, we released the bolts and pulled the motor mount out.
This is what you want to see once the factory header and studs are out. To achieve this level of readiness, you have to remove the nuts and studs from both above and below the vehicle. We are oversimplifying this step but with some skills, you will get to this point.
Kooks supplies a double layer, stainless steel shim gasket that fits between the header and cylinder head.
Kooks also supplies the stainless steel fasteners and locking clips that keep the header bolts from backing off due to vibration and heat. You can install the steel shim gasket and certain bolts before the header goes on since several of the header flange bolt holes are designed with slots that allow you to slip in the header in place so you can thread in other subsequent bolts.
Here are the notches that we mentioned in the header flange. This little design trick makes the installation of the header much easier than headers that don’t include these slots.
Its show time! Slide the header up in position on the passenger side and it will hang on the bolts you previously installed. From here you can thread the rest of the mounting bolts in place.
When reinstalling the starter, note that there are two bolts that hold it in place. The two bolts are different in length so don’t get them confused. Replace all of the parts you removed during the previous operation and carefully lower down the engine after they are in place.
This is a good time to note one of the main design elements that make the Kooks headers perform so well. This scavenger collector design features the collector spike that aids airflow and, as a result, horsepower and torque improvements.
Moving to the driver’s side installation, disconnect the electrical plugs that attach to the steering system and tag them for later.
Before disconnecting the steering link, we zip-tied the steering wheel in place to keep the wheel from spinning - as it would be the case we did not lock it down.
Disconnect the steering link to provide additional room to access the factory exhaust and make room for the new header system.
As we did on the passenger side, we lifted the engine to provide room to allow removal of the motor mount and for obvious other reasons. Do NOT however lift from the bellhousing as you run the risk of cracking it (as shown here!). Remove the motor mount and header (and studs) as you did on the passenger side to make ready for the new header.
Kooks provides these oxygen sensor-wiring extensions (the shorter length of wire in the middle) that clips into the factory sensor looms. With the new headers, the factory wiring is not long enough.
With the factory header out of the car, you can see part of why the Kooks headers generate more power. Note the section of this factory header where the tubing has been dented in to provide clearance. In addition, the collector design is very restrictive.
Each header bolt is torqued in tighten in place and then dressed with a retaining clip that will keep the bolt in its original location. Veterans of old fashioned header installation projects know well the fact that headers often backed off the header bolts after assembly. Well this fixes all that.
We reinstalled the oxygen sensors after first putting a small amount of anti-seize on the threads. Don’t let the picture confuse you, we only used a small amount – really!
Here is a time saving tip: build up the system including the catalytic converters and mid-piping before you install it when you have easy access to the clamps and tubing. Don’t tighten down the clamps however as you will need to adjust them once they are in the car.
Another two-man job: slip the assembled section in place as shown. Note that a dead blow hammer can be helpful in positioning since you want a snug, leak-free connection throughout. Remember DO NOT tighten any of the clamps as that stage – simply snug them up as you will be adjusting all of the tubing once it is hung in place.
The collector to the catalytic converter tubing connection is critical. When finished, your system should look like this. All of the components shown here are included in the kit.
Position the rear tubing sections in this manner. Note that they are different side-to-side and tagged right and left.
These curved sections are also left and right-specific and use the factory hangers and mounts.
After slipping on the mufflers and clamps, we used the factory hanger system again to position them in the chassis.
The crowning touch is the installation of the exhaust tips, which are stepped with shorter exit tube near the outer side of the car. Don’t forget to slip the clamp over before sliding on the tip or they will have to come back off again.
With the oxygen sensors installed along with the wiring extensions, they were kept out of harm by zip-tying them up so they would not catch on road debris.
Once the system is installed, adjust the tubing but turning various sections to make it fit up high in the chassis but away from any other underbody components that would be damaged through exhaust heat.
With the full Kooks exhaust in place it appears like this – a marked improvement over the factory system in every way.
Here is an overview of the dyno results after several pulls on the Dyno Jet. The red line illustrates the factory results and the blue line, the Kooks exhaust, which is dramatically better. In addition to more power, the Kooks exhaust extends the rpm curve up past the 6500rpm mark, which is where the factory header system ceased to generate power. Also Note: this was our result before optimum tuning – a step that should deliver another jump in power and torque.
Photography by Cam Benty