2004 Chevrolet Corvette - Engine Of Desire

A Big-Cube LS7 Transforms A Staid C5 Into An Object Of Automotive Lust

Steve Temple Apr 1, 2009 0 Comment(s)
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Time marches on, which means either finding new ways to keep up or getting left behind. Consider, for instance, the LS7. Drawing from lessons learned on the track in the Corvette C5-R racing program, GM Powertrain included many competition-derived components and design features into this engine, which took factory V-8 performance to an unprecedented level. Displacing 7.0 liters (427 cubes) and producing 505 hp, it became the largest, most powerful production small-block ever produced by GM (not counting the supercharged LS9 in the '09 ZR1).

Now consider the LS1-powered Corvette C5. While its throttle response wasn't nearly as anemic as, say, the unloved '80 LG6's (the only Corvette with a smog-controlled 305), an iron-block LT4 from the mid-'90s could give the LS1 a run for its money. And, as noted above, the later LS engines have demonstrated quantum gains in power and technology.

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That's not to say the LS1 is a weak sister, since it's a great engine with many advances in technology. Like the original small-block, it has proved itself to be a fantastic foundation for extracurricular horsepower exploration. You can get another 100 horses (or more) out of an LS1 just by forcing air into it. But is that necessarily the way to go? Let's take a quick look at those power adders in order to set the stage for replacing the entire lump with an LS7.

Supercharging can provide a quicker hole-shot in relatively short order, as we've recounted in numerous other features in previous issues of VETTE. Note, however, that some units require the installation of a hood with a couple more inches of clearance, and other mods may be necessary in order to accommodate the system's plumbing. Fitment issues can crop up with a turbo as well, and both systems can produce extra heat, requiring careful temperature management. Also worth considering are the extra weight of the blower or turbo, along with an intercooler.

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Tuning modules are a simpler and less expensive way to go, but the improvements in power output are more incremental than dramatic, and ideally they should be used in conjunction with a range of other engine enhancements.

Another option for a quicker launch is switching to a lower (numerically higher, such as 3.73 or 4.11:1) rearend ratio. Problem is, that a change in gearing can have an effect on the car's speedo and antilock brake system, necessitating a full reprogram of the factory PCM. Furthermore, the resulting extra revs not only burn more gas and accelerate drivetrain wear, but they also can drive you batty with all the extra noise. And it's almost as much work to pull out the transaxle as it is to perform a complete engine change, since you have to remove the rear control arms, use a special support jack, and employ other safety equipment.

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How about stroking the LS1? Well, that's all fine and good, but considering the labor and time of sending out the engine for a new crank, installing a new LS7 might make more sense. Let's do the math: Comparing factory numbers, the gain in power is startling-from 350 to 505 horses. And the price of a stroked LS1 can be roughly the same as that of a stock LS7.

Not only that, but even more power is readily available for the LS7 without going to forced induction. On the particular '04 C5 shown here, owned by Mike Jonas of Stainless Steel Brakes Corporation, the engine was reworked by LS-performance specialists Scoggin-Dickey. In addition to throwing on a new set of high-flow heads, this engine builder also opened up the block from 427 to 440 cubes.

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Jonas also threw on a slew of performance parts to reach his goal of exceeding 600 flywheel horses. Comp Cams supplied an aggressive camshaft that emits a hot-rodded rumble through the 2.5-inch Kooks headers and Corsa pipes. (Jonas says there's not enough room for 3-inch tubing.).

The oxygen-sensor-equipped headers are particularly important for maximizing the output of the LS7 while keeping it smog legal, but there are other key elements as well. Chief among them are a larger, 900-cfm throttle body (for compatibility with the LS7's drive-by-wire system) and a K&N air intake fitted with a VaraRam ram-air scoop. With the stock intake setup, the engine tended to run hot and rich, killing both performance and combustion efficiency. But the K&N/VR unit picks up air from under the front bumper, dropping intake-air temperatures by as much as 80 degrees. According to Jonas, that reduction in heat was essential for tuning at idle.

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Other swap-specific hard parts include modified engine mounts as well as a new timing-chain cover, wiring, ECM connectors, and sensors supplied by Katech. (Note that the crank sensor on the LS1 is on top, while the LS7's is mounted on the bottom.) In addition, the LS1 has a wet-sump oiling system, while the LS7 has a dry sump.

With the LS7 nestled neatly in place and up-fitted with performance parts, the next stage involved custom mapping with HP Tuners' VCM Editors Flash system. This utility allows the user to read the VCM/PCM's flash memory and save it to a binary file for calibrating and modifying parameters such as spark, fuel, rpm limits, temperature, transmission shift points and pressures, speedometer settings, and so forth. The unit also features automatic recovery capabilities for protection against any reflashing problems that might be encountered.

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This phase required nearly a month of fiddling and tweaking, as the computer calibrated itself to Jonas' driving style. He's not one to baby his Corvette, having dropped the hammer on several previous rides, such as a '66 big-block coupe, a '72 LT-1, a '78 Silver Anniversary coupe, and a '67 small-block convertible.

Also adding to the car's accelerative credentials are a Fidanza carbon-fiber clutch with a lighter aluminum flywheel. Rolling stock consists of Forgeline three-piece wheels (18x9s up front, 19x11s in the rear) wrapped in Goodyear Eagle GSD rubber (sized 245/40 and 285/35, respectively).

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With all this extra go-power, at some point you've got to think about stopping as well. To bring this hot rod to a halt, Jonas dipped into his company's parts bin, using Stainless Steel Brakes' V-8 calipers. Each one has no fewer than eight pistons (!) to clench the two-piece, 14-inch rotors, which also feature slotting and cross-drilling. Jonas claims the stopping distance from 60 mph is now 113 feet, compared with 125-135 feet with the stock C5 brakes.

Space doesn't permit going into all the other suspension and body upgrades that went into the car, but suffice it to say that the project was a long time in the making. Looking back, Jonas admits it took longer than planned but adds that the Vette "turned out way better than I expected." While not all LS1 Vette owners will be inclined go to these lengths, if they do, they'll be glad to learn that there's a light at the end of the tunnel. And it sure as heck won't be anybody else's taillights.

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