One of Shakespeare's more controversial quotes involves a simple legal maneuver: "The first thing we do, let's kill all the lawyers" (Henry VI). The thing is, we don't run into a lot of car enthusiasts who are fans of Bill Shakespeare (Kill Bill might be more up their alley). Besides, some of our best friends are barristers, and we just came across one really sharp-eyed legal eagle by the name of Steven Young, the owner of the supercharged '08 Z06 shown here (plus a slew of other Vettes). He happens to be the corporate attorney for Magnuson Products, the maker of the car's high-tech windmill, and also is Chairman of the Board at the Petersen Automotive Museum, and a member of the National Corvette Museum.
Young's gigs actually sound like pretty good work-if you can get it. And anybody who has the moxie to bolt a blower on an LS7 is OK in our book. Having driven Young's righteous piece of machinery, we're frankly thinking of enrolling in law school. (On second thought, maybe we'll just watch a rerun of Legally Blonde instead.)
But we digress. A lot. Let's focus on the nuts and bolts of this setup. Magnuson has long employed the tried-and-true Roots-type supercharger, using rotors supplied by the Eaton Corporation. Originally designed in 1860 by the Roots brothers as an air pump with meshing lobes for use in blast furnaces, it eventually found its way onto an engine designed by Gottlieb Daimler in 1900.
"Alas, poor Yorick..." Hamlet, Act 5, Scene 1
That early configuration, though, is about as antiquated as the skull of Yorick unearthed by those two clowns in Hamlet. (By the way, Hamlet never said, ". . . I knew him well.")
Today's version has been substantially refined by Eaton in a number of significant ways, such as using four-lobe rotors on the TVS (Twin Vortices Series) Supercharger, among other changes. It also has a new twist-literally.
These twin four-lobe rotors now have a 160-degree helix shape (roughly similar to a DNA strand). The higher helix angle, along with improved geometry for the inlet and outlet ports, reduces pressure variations, resulting in a smoother discharge of air for higher efficiency over traditional Roots superchargers. With helical rotors and an axial inlet, the Magnuson supercharger can spin up to 14,000 rpm, thus reducing package size.
Another change is in the actual surface material of the rotors, called APC (Abradable Powder Coating), which both looks and feels like extra-fine, wet-or-dry black sandpaper.
"It's a self-honing coating to keep clearances at minimum," explains Magnuson's Bob Roese. This allows the rotor to "wear in" for improved sealing. In addition to these upgrades to the innards of the blower case, the intake ports have been enlarged and a "blowhole" added in the rotor configuration to reduce noise. Moreover, Magnuson adds its own special recipe of components to optimize Eaton's air pump for a particular automotive application.
"Eye of newt, and toe of frog..." Macbeth, Act 4, Scene 1
No witches' brew of arcane performance parts is needed here, though. It all comes down to a few essential items: a blower case, a custom intake manifold, bigger injectors, an intercooler, and a software modification in the engine computer. And one more thing: the whole shebang needs a slightly taller hood, in this case courtesy of RK Sport. Not counting the painting and swapping out of the hood, installation takes at least a day and a half, depending on your skill level (or your mechanic's).
The injectors are 60-lb/hr units, the same as on the ZR1 LS9. The performance software, provided by SCT, changes the injector pulse widths to compensate for the larger injectors, scales them for the addition of the boost when the bypass closes, and alters the timing maps to compensate for the additional air.
Modifying the fuel pump depends on the customer's individual application. Magnuson's Kerry Tresback points out that if a Z06 Vette is left in a strictly stock configuration (with the exception of the supercharger), increasing the pump output by stepping up the voltage with a MagnaVolt unit is not strictly necessary. However, since many Vette owners modify their engines with a hotter cam, headers, and so forth, Magnuson will be including the MagnaVolt component with the Z06 Corvette supercharger system in order to ensure sufficient fuel volume.
As for the intercooler, virtually all superchargers benefit from reducing heat during compression. A decrease in intake-air temperature provides a denser charge to the engine and allows more air and fuel to be combusted per engine cycle, increasing output. In addition, a cooler intake charge allows for higher boost levels without detonation, producing more power.
Note however, that all engines running on pump gas are compression limited. When you add boost to an engine, you are essentially adding compression. Regardless of supercharger style, there is a limit that, if exceeded, can destroy the engine. With 92- or 93-octane pump gas, that limit seems to be 7.5 psi with an effective intercooler.
With the improved efficiencies of Easton's new lobe design, however, lower boost levels (about 4 to 5 pounds in this application) can still furnish exhilarating performance. As Roese points out, "It takes less horsepower to power the unit, so the parasitic numbers are lower, the discharge temperatures are lower. Adiabatic efficiency is the key." The added bonus is less stress on the engine block. (And yes, we've heard too many sad tales about the "best-laid plans of mice and men" going astray due to extremes of forced induction.)
Young has some key words of his own to describe the change from naturally aspirated to a supercharged mill: "Before, it was a very tractable, even docile, street car, but turned into King Kong when I hit the throttle hard. [It's still] equally docile and tractable-no difference at all in street driving-but now when you hit the throttle, it turns into Godzilla. The ZR1s out there can't touch it."
So he's saying there's not just one, but two big bad monsters in one car. We can vouch for this experience personally after stomping on the go pedal. The traction control kicks in pretty quick, so this supercharger has plenty of fire breathing and chest pounding to spare.
"A horse, a horse! My kingdom for a horse!" Richard The Third, Act 5, scene 4
So how much more output are we talking about here? Unlike the hunchbacked villain-king Richard III, who was about to meet his doom at the hands of the future Henry VII, we want more than just a single horse. How many can you corral with a Magnuson 2300 TVS supercharger? According to a company dyno graph, the peak horsepower jumps from a stock figure of 450 to 573.4 hp. That's a gain of 123 horses, more than 27 percent.
Of course, much higher levels are possible with a smaller pulley (2.9 inches is the minimum), but Roese notes that the high compression of the LS7 might require taking some timing out and losing throttle response. So this level strikes a happy balance between driveability and whup-ass acceleration. Case closed.