2008 Ford Shelby GT500 Exhaust Test - Now We're Kookin'
Long-Tube Headers And 3-Inch Exhaust Are The Recipe For More GT500 Power
From the July, 2010 issue of 5.0 Mustang & Super Fords
By KJ Jones
Photography by KJ Jones
There's no arguing that Shelby GT500s are special. The name alone carries a higher level of status among Mustang enthusiasts.
The real reason Shelby GT500s are so special is because Ford installed more factory-developed horsepower in them than in any other Pony before. In the field, we've seen average bone-stock horsepower ranging from the mid-420s to the mid-450s at the feet. Of course, that kind of steam excites hard-core 'Stangbangers, and for those who are addicted to high performance, there's no such thing as too much horsepower.
At this point, we've documented several ways of making bigger steam with Shelbys in the pages of 5.0 Mustang & Super Fords. We've installed more than a few bolt-ons, plus larger superchargers and even turbos, and evaluated them on the chassis dyno.
Replacing the factory upper...
Replacing the factory upper exhaust pieces (cast-iron manifolds) on any mod-powered Mustang is no simple task. On the GT500, the process starts with the battery-and not simply removing the negative cable. Saul completely removes the entire battery package (cell, tray, and so on) and CAI to gain better access to the manifold nuts (stock manifolds are secured on 13mm studs that must be removed and discarded) on the passenger side.
While improved induction usually is the star of the performance show, we can't forget the important role that exhaust plays in the overall situation-especially when an engine's air volume is increased by boost or nitrous oxide.
After-axle exhaust systems are great for street Shelby's that are enhanced with basic bolt-ons. However, when the wick is turned up-for example, with a blower like Vortech's all-new Lysholm twin-screw supercharger-the need for exhaust efficiency requires more than just mufflers.
In this exercise, we're looking at the changes that adding a complete long-tube header system and 3-inch exhaust will make on Sean Roberts' '08 Shelby GT500. Unlike many Shelby GT500 owners, Sean passed on going the systematic route of adding bolt-ons in step-by-step fashion (save for a post-catalytic exhaust that was installed shortly after buying the car), and instead went straight for the gusto, by bolting Vortech's massive, new 3.3-liter huffer on top of his 'Stang's otherwise stock 5.4, as the car's first performance mod. That's some first bolt-on.
As you would expect, the addition of a larger blower on an already-stout engine is going to create a good amount of increased power right off the bat. The aftermarket supercharger offerings for Shelbys raise the horsepower stakes considerably, as they all easily contribute to enabling GT500s to generate almost 800 rear-wheel ponies. However, we're finding that most owners-like our own Editor Turner, for example-are settling on numbers in the high 600s and low 700s as pump-gas plateaus for their Shelbys' performance.
On the underside, removing...
On the underside, removing the stock manifolds requires disconnecting the engine mounts, O2 sensors, and steering linkage. Next Saul removes the OEM catalytic converters and after-cat exhaust. After that, the starter, dipstick, and G-load cross brace are taken out, and the Shelby's 5.4 is raised using a pole jack (thus the reason for needing a twin-post hoist to get this part of the job done). Once sufficient clearance is achieved, the manifolds drop down and out easily.
We had heard quite a bit about Kooks Custom Headers' complete long-tube-header exhaust system for Shelby GT500s ($2,313.97). We got a good look at the system while strolling the aisles of the 2009 PRI show, and wondered how much the headers and mufflers would help a GT500 influenced by big boost.
Sean's ride falls right in step with GT500s with a similar blower upgrade. Prior to our project-installing the complete Kooks exhaust setup on Sean's 'Stang-the car blazed the chassis dyno to the tune of 604.82 rear-wheel horses and 538.16 lb-ft of torque. That figure was achieved with a fairly aggressive 91-octane-fuel tune and exhaust that flows through factory-stock manifolds, catalytic converters, and stock 2 1/2-inch tubing.
Read on through the accompanying photos and captions as Saul "The Surgeon" Gutierrez of Extreme Automotive in Canoga Park, California, takes you through the installation process.
Unlike many bolt-on efforts we report on, this one is not something you want to attempt in your driveway or garage. The process involves raising the engine, and really should be performed by a trained Mustang technician at a facility that is equipped to handle the job.
However, when it's over, we're sure you will have new appreciation for how well a good, freer-flowing exhaust system, like Kooks' long-tube deal, really complements an enhanced-boost Shelby GT500.
Horse Sense: For those of you who haven't heard, the Kooks Custom Headers group has "gone country." That's right. Everyone at Kooks (Papa Kook, George Jr., George R., and their entire workforce), all of them dyed-in-the-wool Noo Yawwkaz, has left the urban confines of Gotham and raised stakes in-for lack of a better comparative term-the country. Kooks tubes are now being produced in the company's spacious new facility in Statesville, North Carolina, just a few miles down the road (as the crow flies) from Charlotte, the big city to area natives.
Here's a comparative look...
Here's a comparative look at the Kooks header (top) and the factory's restrictive cast-iron exhaust manifold. The 304-grade, stainless-steel headers feature primaries measuring 1 3/4x3-inch and Kooks' patented Velocity Spike merge collector. Kooks also offers the headers with 1 7/8x3-inch primaries, for Shelbys that make more than 700 hp.
Note the difference between...
Note the difference between the OEM exhaust gasket (top) and the gasket that's provided with Kooks' header system. While the stock gaskets have a two-piece design, Kooks uses a longer, one-piece seal for mating header flanges to the cylinder heads. It's important to make sure the cylinder heads exhaust-port surfaces are thoroughly scraped clean before installing the new gaskets or reusing the OEM seals.
Saul fits the passenger-side...
Saul fits the passenger-side header in place first, followed by the driver-side tubes. As long as there's sufficient clearance, laying the headers up is the easy part and can be done in either order...
...Securing the fasteners...
...Securing the fasteners is a whole other story. Ford uses studs to install Shelby manifolds. The Kooks headers are fastened with 13mm bolts, which must be treated with a dab of antiseize before tightening them in the heads.
It's actually too bad that...
It's actually too bad that this exhaust system sits below a Mustang and out of sight. Kooks' mandrel-bent, stainless tubes look great and are designed for clean fitment on a Shelby. The system we installed includes the aforementioned headers (PN 6027; $997.36), along with a 3-inch catted X-shaped crossover (PN 6028-CX; $566.61) and a pair of 2 1/2-inch stainless mufflers and mid-tubes (PN 6030; $750), which are also applicable on Three-Valve Mustang GTs.
From up top, the stainless...
From up top, the stainless headers fit without any conflict with steering equipment, engine mounts, or the chassis on either side, and they look much better than the unfinished, plain cast-iron pieces that come with new Mustangs.
This is a look inside the...
This is a look inside the Kooks' metallic substrate cats that are part of the long-tube system we installed. The element inside the smaller (diameter and length) Kooks cats is a lot less restrictive than OEM converters, which is important for supercharged applications.
There's literally nothing...
There's literally nothing inside Kooks' stainless-steel, 2 1/2-inch mufflers to challenge or obstruct exiting exhaust gasses.
Here it is, from front-to-back-Kooks'...
Here it is, from front-to-back-Kooks' Shelby GT500 long-tube header system.
Once all of the pieces are...
Once all of the pieces are in place, Sean's ride is lowered back to Earth and affixed to the chassis dyno...
...where we'll see what type...
...where we'll see what type of difference long-tubes make on a big-boosted Shelby.
On the Dyno
Going into this project, we knew that adding long-tube headers and 3-inch exhaust pipes would promote a nice torque gain for Sean's already torquey '08 Shelby GT500. However, the big surprise was the increased horsepower we saw with the addition of Kooks' long tubes, and a little SCT tuning that was handled by our friend Lance Keck.
It's important to note that while the peak-power number achieved with the headers does look insane, it is derived using a baseline peak of 604.82/538.16. The lower numbers reflects the true, SAE, on-the-ground horsepower and torque (according to a Dynojet chassis dyno) that the GT500 had on tap as Sean drove it around with the bone-stock exhaust.
However, the bottom line is that the Kooks exhaust system and sharp tuning made an impressive performance gain on Sean's mega-blown Shelby, and it opens the door for easily going straight to the engine's threshold, with the addition of higher-octane fuel and tuning.