C6 Corvette Bolt-Ons - LS3 Power Play

Xtreme Motorsports' Bolt-On Package Adds 60 HP And 46 LB-FT Of Torque

Dave Emanuel Apr 13, 2009 0 Comment(s)
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With the headers bolted in place, the catalytic converters are installed. As seen here, the 3-inch collectors bend around the frame and bellhousing with plenty of clearance.

Harwood and Burch have also developed an alternative package that incorporates 1 7/8-inch headers and a Random Tech 3-inch converter/cross-pipe exhaust-system assembly. In addition to fitting C6 Z06s, this package can be installed on LS2- and LS-3-powered C6s and connected to a pair of Z06 mufflers to create a full 3-inch exhaust system. The intent of this configuration is to provide maximum power with no drone. (That system wasn't installed on this particular vehicle because it had the optional dual-mode LS3 mufflers.)

According to Harwood and Burch, with either system, the headers and converter/cross-pipe assembly are relatively easy to install. Once the original exhaust manifolds have been removed, the headers slip into place with a minimum amount of pushing, shoving, cussing, and bleeding. The passenger-side header slips in from the top, while the driver-side is more easily moved into position from beneath the car.

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Since the catalytic converters are designed specifically to fit the Melrose headers, they slip into place with a minimum of fanfare, scraped knuckles, and expletives.

It's actually easier to install headers on a C6 than on a C5. LS2 and LS3 engines aren't equipped with an external air pump, so the headers don't require an external plumbing or connections. Minor changes in the chassis and drivetrain also reduce installation obstacles. According to Harwood, "I really like the Melrose headers. They're easy to install, fit very well, and make great power."

Slip fits between the headers, converters, cross-pipe, and exhaust system continue the easy installation theme. Band clamps, which overlap the collector on one end and the converter on the other, assure leak-free connec-tions, as do the original clamps at the cross-pipe-to-exhaust system joints. Harwood typically welds the remaining connections, where the converter out-lets slip into the cross-pipe, but clamps are also an option.

As a complement to the exhaust enhancements, the Xtreme package includes a Callaway Honker to bring a higher volume of cold air to the throttle body. The Honker achieves its airflow advantage through a replacement filter element and housing in combination with a modification to an existing shroud. That modification allows cold air to flow directly to the filter element.

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To keep an eye on things during test runs, Xtreme Motorsports' Chris Harwood keeps an eye on an EFILive programming/scanning handheld and Innovate wide-ban controller. Both units are mounted on a specially constructed stand.

As is obvious from the dyno charts, the Xtreme LS3 package works "Xtremely" well, delivering 431 hp and 412 lb-ft of torque--increases of 60 hp and 46 lb-ft over the maximum readings recorded prior to modification. As impressive as those numbers are, they don't tell the whole story. Although large numbers at the top end of the horsepower and torque charts are important at bench-racing sessions, "my Corvette is faster than your Corvette" fests and other verbal contests, they don't have much influence on normal street and highway driving. On the other hand, midrange torque brings an ear-to-ear grin to a driver who slowly rolls into the throttle when pulling away from a traffic light or the idiot in the next lane.

In addition to the improvement in peak power levels, the Xtreme package also delivers torque increases of more than 15 lb-ft from 2,200 to 3,000 rpm, 20 lb-ft from 3,100 to 3,300 rpm, and 30 lb-ft from 3,400 to 3,800 rpm. At 3,900 rpm and above, torque increases are 40 lb-ft or more. Keep in mind that throughout all the testing, the '08 C6 was in emissions-compliant, street-legal form.

But that's just the tip of the iceberg. If an LS3 (that has literally never even had its valve covers removed) can put 431 hp to the ground through an automatic transmission, consider its horsepower potential after a set of ported heads and performance camshaft are installed. Do I hear 500 hp, anyone?




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