2008 Jeep Grand Cherokee SRT 8 Upgrade - Kooks Custom Headers

When people bolt-on headers to their vehicle's engine, their main satisfaction is the throaty sound they produce. Sure the sound is impressive, but more importantly from a performance aspect, the headers will improve the engine's throttle response, torque, hp, and fuel mileage.

What makes the OEM exhaust manifold and header swap such a noticeable improvement is the header's inner diameter and the equal length tubes. These two factors affect the burnt gasses flow rate, or velocity, as the gasses exit the exhaust ports of the cylinder heads and are propelled by the compression release of each of the exhaust ports, known as pulses. The headers increase the velocity of the burnt gases as they travel through the exhaust system, thus increasing both torque and horsepower.

The '08 Jeep Grand Cherokee SRT-8 is a real beast from the factory with its 6.1L Hemi V-8 producing 420 lb-ft of torque and 420 hp. With AWD and that much power on tap, the SRT-8 launches like a dragster, but like all gearheads, more power is always better. To increase the mighty SRT-8's grunt, we decided to bolt on a set of Kooks Custom Headers and high-flow pipes that connect the headers to the factory catalytic converters. These Kooks power tubes, when combined with Kooks' high-flow cat pipes, have been dyno-proven to increase the engine performance by 28 hp. That's a huge increase in bolt-on power and the better-breathing 6.1L also sounds like a street-ready assassin.

We delivered the Grand Cherokee SRT-8 to Traders Sport Truck, in Santa Fe Springs, California, where Mike Bogart, Traders' technician specialist, installed the Kooks Custom Headers and high-flow cat pipes.

Kooks Custom Headers PN6920 (headers) and cat pipes PN1002741 are constructed from 304 stainless steel. The headers have a 3/8-inch thick flange, 18-gauge 17⁄8-inch-diameter tubes, and flow into a 3-inch-diameter collector. Three-inch stainless steel cat pipes link the Kooks headers to the factory catalytic converters. To eliminate header flange leaks, Kooks uses Percy's High Performance 3/8-inch thick carbon gaskets. A pair of Kooks O2 sensors replace the factory sensors.
Kooks Custom Headers PN6920 (headers) and cat pipes PN1002741 are constructed from 304 sta
Before attempting to remove the OEM exhaust manifold, Mike had to remove the frame crossmember.
Before attempting to remove the OEM exhaust manifold, Mike had to remove the frame crossme
After removing the passenger side exhaust manifold bolts, Mike was able to remove the OEM exhaust manifold.
After removing the passenger side exhaust manifold bolts, Mike was able to remove the OEM
Peering up into the engine compartment from underneath, we could see how tight the 6.1L V-8 fitment was.
Peering up into the engine compartment from underneath, we could see how tight the 6.1L V-
This comparo shot gives us a good idea of the design difference between the OEM manifold (left) and the Kooks header. The factory exhaust manifold was dwarfed by the much larger Kooks long-tube header. The burnt gasses flow rate and velocity will be highly increased, producing more torque and hp.
This comparo shot gives us a good idea of the design difference between the OEM manifold (
Mike carefully maneuvered the Kooks header up into position.