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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The electronic fuel-injection systems that have been installed on Corvettes since the early '80s have improved dramatically over the years. So has the tuning software that provides the capability to enhance factory calibrations. The result of all this electronic wizardry is a series of engines that produces more power, delivers better fuel economy, and generates lower exhaust emissions than would otherwise be achievable. But beneath all the wiring harnesses, sensors, relays, and controllers are engines that still require air, fuel, and internal combustion to create torque, horsepower, and carbon footprints.

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With a displacement of 6.2 liters (376 ci, if you don't speak metric) LS3 engines produce 430 SAE net horsepower (436 with optional dual-mode exhaust system) in stock form--a few well-chosen modifications that really come alive.

That being the case, the recipe for a hearty "horsepower cake" still requires the proper mechanical ingredients; electronic alterations are simply the icing on that cake. The performance packages developed by Chris Harwood and Wes Burch of Xtreme Motorsports in Blountstown, Florida, address that fact by using selected mechanical components along with ECM/PCM calibrations developed for each combination of mechanical components.

One of the latest Xtreme packages includes a selection of bolt-on components designed for '08 and '09 LS3-powered Corvettes. It consists of Melrose long-tube headers, Random Technology high-flow converters and cross-pipe exhaust system, Callaway Honker cold-air system, 10mm plug wires, and custom tuning. Noticeably missing from the package is an aftermarket exhaust system. According to Harwood, "We have a lot of customers who really hate the drone you get with a lot of aftermarket exhaust systems, so we put together a basic package that keeps the stock mufflers. If noise isn't an issue, or if a customer likes the tone of a certain system, we can always add it to our package. We've found most low-restriction systems are good for 8-10 hp at the wheels compared to the dual-mode stock mufflers."

Considering the 60 hp and 46 lb-ft of torque increases delivered by the Xtreme package, the stock mufflers obviously aren't all that bad. And with headers and high-flow converters in place of the stock components, the exhaust is relatively quiet, yet has a surprisingly authoritative tone even when the bypass valves are closed.

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The stock LS3 exhaust system is manufactured of 2 1/2-inch-diameter tubing and includes a cross-pipe exhaust between the catalytic converters and the mufflers.

All LS-series engines respond well to exhaust-system components that provide improved airflow capacity, but the LS3 is particularly responsive, owing largely to its 6.2L displacement and large-diameter valves. Although the exhaust valves are only marginally larger than those used in LS1 and LS2 engines, the LS3's 2.16-inch intake valves and 4.060-inch bore diameter translate to increased exhaust volume at the end of the combustion cycle. Consequently, modifications that improve exhaust flow provide an extremely attractive repositioning of horsepower and torque curves.

Long-tube headers are particularly beneficial when installed on engines with above-average breathing capability. The ceramic-coated Melrose headers included in the Xtreme package feature 1 3/4-inch primary tubes and 3-inch-diameter collectors. They connect to a pair of Random Technology SuperStainless catalytic converters, which feed into a 3-inch Random Tech stainless steel cross-pipe exhaust system. As a means of optimizing exhaust flow, the cross-pipe retains a 3-inch diameter all the way back to the exit end, where the pipes are reduced to 2 1/2-inch diameter so they fit the stock pipes that lead to the mufflers.

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