Going GREEN: Adding Kooks H.O. Cats To A ZL1 And Making 800WHP

As automotive and high-performance enthusiasts, it is difficult for us to leave vehicles alone. Our minds are always thinking of ways to modify and improve our cars. Truth be told, we are often thinking of how to modify vehicles that we don’t own. So when we got our hands on a 2022 ZL1 Camaro, we were like children with a new toy. The sixth-gen ZL1 is an impressive combination of technology and power, and represents the pinnacle of Camaro performance. Being the gearheads we are, we couldn’t just leave our ZL1 alone. So we put a plan together to improve upon our Rapid Blue beast with products from ZPE, DSX Tuning, Xtreme-DI (XDI), and AEM. Because our ZL1 came to us with the factory catalytic converters deleted, we first wanted to install a pair of Kooks catalytic converters to make the car a little more environmentally friendly. Additionally, we wanted to prove that gone are the days of needing to cut the cats off your car to make lots of power. 

Kooks H.O. cats

Our 2022 Rapid Blue ZL1 Camaro is a perfect candidate for a few modifications that will take it from a factory muscle car to a street terror.

A Factory Muscle Car On Steroids

As much fun as it is to start from scratch and create a recipe to take a car from stock to modified, this project is much spicier. As it turns out, the previous owner of our ZL1 is a high-performance enthusiast like us, and also like us, couldn’t leave the ZL1 stock. This car rolled into the shop with a laundry list of upgrades and modifications. Most notable is the Kong Stage X ported factory supercharger. Kong is well-known for its CNC-porting services and the Stage X upgrade includes additional CNC machining that Kong has extensively flow simulated, dyno tested, and proven on the track. According to Kong, with the Stage X upgrade to the LT4’s factory 1.7-liter supercharger, 1,000 wheel-horsepower is achievable with supporting modifications and fueling.

Kooks H.O. cats

This ZL1 already had several modifications when it came to us. The biggest of which is the Kong Stage X ported factory supercharger.

To support the Kong blower, an RPM camshaft was installed along with PAC dual valve springs, LS7 lifters, a 0-degree camshaft phaser limiter from Texas Speed & Performance, and a billet timing chain set from Late Model Engines. An 18-percent overdriven lower pulley from Lingenfelter Performance Engineering (LPE) spins the blower faster to take advantage of Kong’s porting work while a Nick Williams 103mm throttle body allows the blower to swallow more air. Kooks long-tube headers and a Borla Atak exhaust system move spent gases out the rear. Other parts already installed on our ZL1 included an ATI Performance Super Damper, an upgraded heat exchanger, and an LS9 idler pulley from LPE.

Turning The Wick Up

For some enthusiasts, a car with this combination of modifications would be plenty. During the “before” dyno testing, our ZL1 produced 768 wheel-horsepower, enough to make daily commutes exciting. However, we wanted to push the ZL1’s LT4 engine a bit more and change a few things on the car while we were at it.

The Borla Atak exhaust and cat-delete sections were on the ZL1 when we got our hands on it. We'll be keeping the Borla exhaust system but we are replacing the straight-pipe sections with Kooks GREEN High Output (H.O.) catalytic converters.

When we acquired the car, its exhaust system was sans factory catalytic converters. Removing the catalytic converters is a somewhat common practice to create a more free-flowing exhaust to improve performance. Unfortunately, this modification is also not legal for street-driven vehicles and will typically cause the car to fail smog testing if you live in an area that requires it. Additionally, the tone from an exhaust system that is “straight-piped” tends to have a droning sound that can be unpleasant for daily driving. Straight-piped exhaust systems also tend to emit the smell of raw fuel. To combat these issues, we wanted to install new catalytic converters on our ZL1, but we didn’t want to give up any performance. Because the car already has Kooks long-tube headers installed, we reached out to Kooks’ Becky Sliney to get her recommendation for a catalytic converter that would suit our needs.

Going GREEN With Kooks H.O. Cats

Catalytic converters work by creating a controlled environment where chemical reactions can occur to reduce pollutants. However, the restriction they introduce can be problematic for high-performance engines, which generally require unrestricted flow for optimal performance. This restriction can cause a loss of power and efficiency, making them highly undesirable for high-horsepower applications. Fortunately for us, these problems are a thing of the past thanks to the engineers at Kooks. By increasing the catalyst’s efficiency, they can increase cell spacing, dramatically improving flow.

After discussing the current modifications on the ZL1 and our planned upgrades, Sliney recommended a pair of Kooks High Output (H.O.) GREENCATS catalytic converters. “These particular cats are geared towards performance builds,” Sliney says. “They are rated for up to 1,000 wheel-horsepower and are designed for use on [naturally aspirated] or forced induction applications.”

Kooks H.O. cats

The Kooks H.O. GREENCATS are a high-performance replacement that flows more than factory cats and won’t hinder your high-horsepower build.

With little to no power loss, you get the best of both worlds. — Beck Sliney, Kooks Headers & Exhaust

The Kooks H.O. GREENCATS are a larger diameter than the standard cats and have fewer cells inside them to increase air flow.

“The [H.O. GREENCATS] are housed in a larger body and have a lower cell count than our regular GREENCATS to further enhance the flow,” Sliney explains. “The Kooks cats are 4.5 inches in diameter and have a 300 cell count, as opposed to the regular GREENCATS being only 4 inches and 400 cells. They’re perfect for drivers who want performance, but don’t want to deal with the smell of raw fuel or the drone of a competition [exhaust] system.”

Installing the new cats from Kooks is a simple and straightforward process. With the ZL1 up in the air on our BendPak lift it’s easy to access the sections of the exhaust system that need to be removed and replaced with the new cats. Our resident technician, Seth Ward, made quick work of the installation. After removing the O2 sensors from the straight-piped sections and loosening the clamps on each end, the short sections can be removed. To install the Kooks cats, Ward slid them on the headers, connected the exhaust pipes, and tightened the clamps. Once the O2 sensors were threaded into the cats the installation is complete. “The Kooks cats just bolted right up, and the overall fitment is great,” Ward says. “The sound is better now, and the smell of fuel is gone.”

Installing the Kooks H.O. cats is a simple bolt-in process made easier with the car in the air on our Benpak Lift.

More Boost + More Fuel = More Smiles Per Mile

Along with adding the Kooks H.O. GREENCATS, we wanted to get more boost from the Kong Stage X blower. To achieve this we installed a ZPE Griptec 2.30-inch supercharger pulley and a shorter Gates green HD belt. When trying to make more boost with a supercharger, belt-slip is a concern. So we installed an upgraded idler pulley bracket from DSX Tuning that keeps more tension on the belt.

To increase boost from the supercharger we installed a smaller 2.30-inch ZPE Griptec pulley. The flex fuel sensor and boost pump kit from DSX Tuning allows us to run E85 and supply enough fuel to the engine to support more power.

To support the additional boost and horsepower, we upgraded the ZL1’s fuel system with a boost pump kit and ethanol-content sensor from DSX Tuning, and a set of DI injectors from X-treme DI that flow 30-percent more fuel than the factory injectors. To better track the air-to-fuel ratio in real-time, we also installed an AEM wideband O2 sensor.

Ryne Cunningham of BRC Raceworks has over a decade of experience tuning high-horsepower late-model EFI combinations. While we had the car on the dyno at The Viper Shop, Cunningham was able to tune the car remotely.

With the installations complete we needed to have the ZL1 tuned again to take full advantage of our modifications. We brought the car to The Viper Shop to get it on their chassis dyno. Ryne Cunningham of  BRC Raceworks worked his magic on the tune remotely while we made pulls on the dyno at The Viper Shop. Cunningham has over 15 years of experience tuning late-model EFI cars and is accustomed to working with modified engine combinations. Because we installed the ethanol-content sensor in the fuel system, he tuned the car for a blend of 40-percent E85 and 60-percent 91-octane pump gas. It only took us a few rips on the dyno while Cunningham uploaded his changes to the tune to get the ZL1 dialed in.

Kooks H.O. cats

These two pulls on the dyno with the blower pulley change and supporting fuel system upgrades show us the ZL1 is making over 800 wheel-horsepower. The car has a broad smooth power band thanks to the tuning abilities of Ryne Cunningham.

We are happy to report the car now makes 814 wheel-horsepower and 789 lb-ft of torque on 15 to 16 pounds of boost. That’s a gain of 46 wheel-horsepower and the best part is the car is making more power with the Kooks H.O. cats installed. Overall, we are impressed with the new cats and happy with how the ZL1 turned out. Having an 800-plus wheel horsepower car that drives similarly to the way it did from the factory is a testament to making the right modifications and Cunningham’s tuning abilities. What a time to be an automotive enthusiast.

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Jeremy Nichols

Jeremy loves to go fast, whether that's on two wheels, four wheels, or boating. With a willingness to compete at almost anything, Jeremy shoots competition long-range rifles matches and races road bicycles and enjoys building vehicles for people.
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