KJ Jones
Brand Manager, 5.0 Mustang & Super Fords
June 1, 2010
Photos 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.

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.

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.

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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.

BaselineKooksDifference
RPMHPTQA/FHPTQA/FHPTQA/F
3,000280.22491.4311.40304.27532.6411.6724.0541.210.27
3,100284.77482.8311.20315.97535.3611.6531.2052.530.45
3,200302.28496.3311.20327.98538.2711.7125.7041.940.51
3,300313.64499.2511.20342.14544.5411.6528.5045.290.45
3,400325.65503.0211.10354.15547.0511.6328.5044.030.53
3,500331.79497.8411.10367.90552.0711.6936.1154.230.59
3,600349.35509.6111.20381.14556.0411.6331.7946.430.43
3,700355.74504.9711.40391.75556.0711.7936.0151.100.39
3,800374.45517.5411.50408.96565.2211.8434.5147.680.34
3,900386.88521.0311.50424.32571.4411.9037.4450.410.40
4,000397.75522.2711.50434.09569.9711.8136.3447.700.31
4,100406.16520.2611.40447.64573.4011.7141.4853.140.31
4,200422.81528.7011.50465.38581.9611.7342.5753.260.23
4,300436.33532.9411.60477.05582.6811.7340.7249.740.13
4,400446.21532.6311.70492.04587.3211.8545.8354.690.15
4,500461.09538.1611.70506.57591.2211.7545.4853.060.05
4,600468.89535.3611.50516.17589.3611.7347.2854.000.23
4,700479.63535.9511.50528.43590.5011.7348.8054.550.23
4,800488.33534.3511.50539.09589.8611.6550.7655.510.15
4,900501.15537.1611.60553.58593.3511.6552.4356.190.05
5,000508.07533.6911.60561.16589.4711.5953.0955.78-0.01
5,100520.76536.2911.40568.44585.4111.7347.6849.120.33
5,200525.91531.1911.30575.57581.3311.7549.6650.140.45
5,300537.06532.2011.40587.01581.7111.6349.9549.510.23
5,400546.45531.4911.50597.69581.3211.7151.2449.830.21
5,500555.31530.2911.70601.52574.4411.5946.2144.15-0.11
5,600563.56528.5711.80610.73572.7811.5747.1744.21-0.23
5,700566.99522.4411.80616.00567.6111.5749.0145.17-0.23
5,800574.77520.4711.70625.61566.5211.6150.8446.05-0.09
5,900582.49518.5311.80627.21558.3311.6344.7239.80-0.17
6,000587.66514.4211.90632.47553.6411.7944.8139.22-0.11
6,100594.80512.1211.90638.32549.60 0.0043.5237.48-11.90
6,200597.45506.1212.00640.77542.82 0.0043.3236.70-12.00
6,300597.97498.5212.00649.06541.10 0.0051.0942.58-12.00
6,400600.05492.4411.90651.38534.55 0.0051.3342.11-11.90
6,500600.74485.4212.00657.40531.21 0.0056.6645.79-12.00
6,600604.82481.3111.90653.86520.50 0.0049.0439.19-11.90