Chevy Corvette C6 Gets Added Power- Bolt-On Thrash

Exhaust And Power Tuning Nets 40 Horsepower!

Randall D. Allen May 1, 2006 0 Comment(s)
0605gmhtp_01_z Chevy_corvette_c6_gets_added_power Underside 1/1

In stock form the C6 LS2 belts out 400 horsepower, with 400 lb-ft of torque from its 6-liter displacement. In part, the increases in power over the LS1 were due to redesigns of the exhaust manifolds and catalytic converters. GM's LS2 manifolds received changes to accommodate revised emissions equipment, but more importantly to increase performance and reduce weight. A 4 percent flow increase and a 33 percent weight reduction were achieved by decreasing the manifold's wall thickness from 4 mm to 3 mm. The C5's previous quad catalytic converter setup was replaced by a more advanced, next generation set of converters, mounted closer to the exhaust manifolds. Not only do they flow better, they also yield cleaner emissions, without the use of auxiliary "pup" converters. Chevrolet didn't stop at the converters as both the mid-pipe and cat-back were redesigned. Backpressure was reduced while flow increased by replacing the C5's laterally mounted muffler with higher-flowing twin-inline mufflers. For a factory system, the C6 exhaust is good, but can it be improved upon?

Whether it's the sound of a tri-power coming in on the outer barrels or a high-revving small-block shrieking as you hit the redline, there's something the enthusiast can't get enough of--power--and the sound of power. Those sweet sounds of the byproducts of combustion are intoxicating, and often, the first modification an enthusiast will make will be to free up the exhaust system for some added power.

Follow along as we install and test a set of Kooks headers, Kooks mid-pipe with high-flow cats and a Corsa Sport cat-back exhaust on a 2005 C6, owned by Garett Oliphant of Houston, Texas. After wrenching and replacing the parts, we'll show you how much power was added to a bone stock C6 and then let Motorsport Technologies (MTI) owner, Jayson Cohen, tune the car to extract every last drop of power.

Technician Chris Ehrlich of MTI will handle installation of the exhaust at the 12,000-sqare-foot facility in Houston, Texas. With 12 years of experience building and tuning the fastest late model offerings from the General, almost anything is possible when you have a fully-equipped machine shop, state of the art flow bench, chassis dynamometer, multiple service bays, and an extensive product showroom

Recommended Tools:Metric Socket setMetric wrenches3/8-inch socket wrench7/8-inch wrench7/8-inch O2 socket5/8-inch plug socketPry bar or large screwdriver

Recommended Parts and SuppliesO2 sensor extensions--12-inch (2) or two sections of 12-gauge wireAnti-seize compoundWire wheel or wire brush

Conclusion:When the C6 bolt-on thrash concluded and the DynoJet rollers stopped spinning, it was obvious that the LS2 engine responded in a big way to exhaust and tuning changes. A total of 40 horsepower and 38 lb-ft of torque was coaxed out of the engine with increases all the way across the power band. The combination of the Kooks headers and mid-pipe with high-flow cats led the pack with an outstanding gain of 20 horsepower and 20 lb-ft of torque. The large 1 7/8-inch stainless steel headers with 3-inch collectors effectively pull out the power, without sacrificing the low-end. Although the Corsa Sport Exhaust showed only modest gains with 8 and 6 hp/lb-ft increases, the excellent tone and looks of the system are in themselves worth the price. What aren't documented are the gains that the Corsa system will achieve as you bump up the power levels and the stock cat-back becomes a restriction. According to Jayson Cohen, "Had we back-fitted the stock exhaust onto the car and tested it with the Kooks headers and mid-pipe with high-flow cats, you would have seen a decrease in the power gained from the headers, as the stock cat back would have become a restriction. This is one case where the parts are chosen based on the total impact rather than just on a part-by-part basis. As the power production is stepped up, the Corsa exhaust plays a more important role, assuming of course that you don't restrict the engine by improper header and/or mid-pipe selection. Equally as important in the equation is the effect of tuning. LS2 Edit now has the functionality required to tackle the most demanding LS2 tuning issues, including supercharging and turbocharging." MTI custom tunes each customer's car and adjusts timing maps, fuel enrichment tables and a long list of other items to maximize the power. In this case, Jayson found 12 horsepower and 12 lb-ft of torque. Gains on stock C5 and C6 Corvettes are usually around 12-15 rear-wheel horsepower, while as stock F-body is closer to 10 and a GTO almost 20 rear-wheel horsepower. Cohen says, "Each GM model has slight differences in the way the computer is tuned for the 'perceived end-user'. In the case of the C6, the untouched PCM has a mid-level timing table and slightly rich air/fuel table. Our specialty is solely GM Gen III and Gen IV engines and that gives us an edge over competitors who are overly diverse."

According to C6 owner, Garett Oliphant, "In stock form the C6 had great power, but having had previous experience with a 2004 Z06 that MTI modified with a head/cam package, I longed for a bit more power and a sweeter exhaust note. The Z06 was ultra reliable and powerful and sold me on having MTI modify my C6 for additional power. The combination of parts and the tuning that was performed on the C6 makes a tremendous difference. Forty rear-wheel horsepower from exhaust and tuning is phenomenal and the changes have really brought the C6 to life. Power is enhanced all across the RPM band, but I really enjoy revving the C6 near the redline to hear the Corsa cat-back belt out some sweet music. Cruising around town or driving on the highway produces no audible interior resonance, so to say that I am happy with the total package is an understatement. Since I had plans to have MTI perform one of its heads/cam packages to the car down the road, it was comforting to know that the exhaust can support the additional power without being a restriction. I love the sound of the Kooks and Corsa exhaust system and with some better flowing heads and some more camshaft lift and duration, it's only going to get better."

You can pick up a set of Kooks 1 7/8-inch headers with mid-pipe and high-flow cats for $1,494. Without cats, the system runs $1,299. The Corsa Sport cat-back with twin 3.5-inch tips goes for $1,224.99. Installation of the complete system, including dyno testing, can be performed at MTI in one day. A highly skilled enthusiast can complete the installation in 6 to 8 hours, but will still need to either send the PCM into MTI for a mail-order tune or visit the local professional late model specialist. C6 owners, your ship has come in, now go get you some power!

Key Engine Parameters: Maximum values noted, *unless otherwise noted

Dyno
Configuration AIT HP RPM Torque RPM +/- HP/TQ
Stock 70.4 344 6,000 352 4,500 N/A
w/Corsa Exhaust 67.5 352 6,000 358 4,500 8/6
w/Corsa and Kooks 66.2 372 6,000 378 4,500 20/20
w/Corsa, Kooks, tuning 66.2 384 6,000 390 4,500 12/12
Total   384   390   40/38

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