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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