Jim Smart
January 17, 2017

It can be viewed as remarkable how far Ford has come since the rebirth of a real factory performance pony in 1982. In 1982, Ford called it the “BOSS” with its 5.0L High Output two-barrel V-8 and four-speed SROD transmission. That was 35 years ago after a very dark period of “lo-po” Mustangs throughout the 1970s. When Ford announced the exotic flat-plane crank Shelby GT350 in 2015 few of us could believe it would actually come to pass let alone think it could be as good as it is.

The 2015-2017 Shelby GT350 is the hottest, most exotic Mustang ever done in the company’s history. That said, how does the automotive aftermarket make this thing better? We make it better with well-thought-out performance modifications conceived by the best minds in the industry. Kook’s Headers & Exhaust can be counted among these great minds thanks its great reputation in the racing industry since 1962.

Founded in the cradle of stock car racing in the heart of North Carolina, George “Papa” Kook built his first set of headers for the family race car over a half-century ago. His great talents did not go unnoticed by the locals. Papa Kook competed at regional dragstrips. For the past 55 years Kook’s has focused its efforts in racing. It’s what they do. Kook’s Headers has helped set records and win races for longer than most of us have been alive. Some of the biggest and most dominant names in NHRA, IHRA, NMCA, NMRA, NASCAR, SCCA, and NASA continue to run Kook’s headers and win championships.

So, what about a Kook’s stainless exhaust system for your 2015-2017 Shelby GT350? Kook’s’ long-tube stainless steel headers for Mustang GT and Shelby GT350 come with either 1 ¾-inch or 1 7/8-inch primaries and three-inch collectors.

Other exciting features include
• Thick 3/8-inch laser cut flanges
• Welded oxygen sensor bungs
• Scavenging spikes in the collectors
• Ball-and-socket collectors

Kook’s 2015-2017 Mustang GT and GT350 headers connect at the factory exhaust system point with OEM-style flanges and pipes. What’s more, they’re available with the Kook’s Ultra High-Performance GREEN catalytic converters, standard race cats, or void of cats completely. These striking stainless headers and complete exhaust system provide astonishing performance gains on the order of 30 horsepower and 20 lb-ft of torque with some performance tuning.

Polygraph Room
HP TQ
Stock 456.51 @ 7,190 rpm 363.29 @ 4,780 rpm
Kook's 481.52 @ 7,390 rpm 379.51 @ 5,930 rpm
Gain 25.01 16.22

1. The factory GT350 exhaust system is a cool twin-cat X-pipe package feeding into resonators. These are designed to deaden extremes of exhaust harmonics before these pipes make their way to a pair of sophisticated mufflers at the rear valance.

2. Each side has a vibration dampener, a cylindrical chunk of steel bolted to the cat designed to dampen the raw vibration generated from the flat-plane crank 5.2L Voodoo engine. These dampeners get transferred to the Kook’s exhaust system. It is the dead weight of these dampeners that “dampens” the engine’s vibration.

3. The GT350’s stock mufflers are very specific to the GT350 with a motorized volume control, which affects tuning and noise levels. The Kook’s system performs the same function using these actuators.

4. First order of business is to remove the air intake system for access to the left hand side headers. Battery must be disconnected and removed along with the battery box to gain header access on the right hand side.

5. Vibration dampeners are removed for transfer to the new Kook’s stainless exhaust system.

6. The GT350 sports abundant plastic aero shielding underneath to reduce drag at high speeds. It all has to be removed front and rear to gain exhaust system access. This is the rear aero shield, which is secured with plastic rivets.

7. Catalytic converters are disconnected from the factory shorty headers on each side using a 13mm box-end wrench. O2 sensors are carefully disconnected and transferred to the Kook’s system when installed. Don’t get the O2 sensors reversed. They must go back in the same locations.

8. The factory system is dropped as a large subassembly ahead of the tailpipes and mufflers; mufflers and tailpipes are easy to remove.

9. GT350 mufflers have exhaust tuning actuators operated from the driver’s seat. Semi-quiet for the morning commute (yeah right) and loud when it’s time to get it on. These actuators are transferred to the Kook’s exhaust system.

10. The steering shaft is disconnected to gain access to the left hand header. O2 sensors have been disconnected.

11. Starter removal is next to gain right hand header access.

12. Engine mounts are disconnected at the subframe as shown in order to tip the engine right or left for header removal and installation. Ultimately, engine mount brackets have to be removed for header access. Engine and transmission are jacked at the bellhousing to gain clearance.

13. Header flange nuts are removed with a 13mm deep well socket and a long extension. Some header nuts are accessed from above. Headers are swapped right hand side first, then, left hand because it is impossible to do both at the same time.

14. Kook’s stainless steel long-tube headers are among the nicest we’ve ever installed, exhibiting outstanding quality and craftsmanship. They sport nice 3/8-inch thick flanges and ball/socket collectors that tie directly to the Kook’s cats. Kook’s provides new exhaust gaskets and O2 sensor extension plugs.

15. Here’s the mid-ship exhaust plumbing package that includes the Kook’s GREEN cats. Brackets are welded in place for the vibration dampeners.

16. Tailpipes and mufflers include provisions for the exhaust tuning actuators. You can use the factory rubber exhaust hangers, which are not included.

17. Right hand side Kook’s stainless long-tube header is fitted and fastened using locking header bolts included in the kit. Do not tighten the bolts until the engine mount is installed and tightened. Factory header studs are removed from the cylinder heads. Do not throw the factory header studs away; instead, put them away in a safe location.

18. Right hand engine mount installation can be very frustrating, so be prepared. Raise the engine as high as possible and keep the header loose for flexibility in order to get the mount secured.

19. You can use an engine hoist to raise the engine and transmission for header access or jack the bellhousing as shown at its strongest point. Be mindful of what’s on top to prevent any damage.

20. Left hand engine mount is a cakewalk compared to the right hand. Removal is easy; steering shaft has been disconnected, do not turn the steering wheel or move the front wheels, and be sure to have it centered going in.

21. Exhaust header studs must be removed and locking header bolts used on the Kook’s stainless steel headers.

22. Left hand long-tube header is easy to install and secure. Engine mount is easy to reinstall. Reconnect the steering shaft using a thread locker and a lot of twist.

23. Kook’s stainless steel exhaust system is completely installed and good to go. We like the streamlined nature of these GREEN cats. O2 sensors have been installed and connected. And we appreciate the good craftsmanship exhibited by both Kook’s and Addiction Motorsports.

24. Cool stainless plumbing flows aft to separate tailpipes and sport-tuned mufflers. The Kook’s stainless exhaust system is easy to install; the toughest part is the long-tube headers not due to header design, but the tight nature of the Voodoo engine compartment and Mustang chassis.

25. Kook’s stainless mufflers deliver a snarly bark at the tips. Open up the electronic exhaust butterflies and this beast sounds unlike any Mustang you’ve ever heard.