Natural Inspiration

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Katech’s $9,400 Street Attack package is rated at 600 horsepower. Since Harding’s car was treated to that and then some, his engine was likely putting out more than that. Still, he began thinking about ways to extract even higher output from the engine while keeping it streetable. A few years down the line, he came up with a solution: He decided to convert the V8 to run on E85 ethanol. Because this fuel’s 105-octane rating is considerably higher than that of the 93-octane gasoline the LS7 was originally tuned to sip, the engine’s compression ratio could be raised to 12.0:1 without sacrificing ignition timing, thus providing a noticeable bump in horsepower production.

Achieving this greater squeeze didn’t require yet another new set of pistons, however. Instead, Harding had the stock cylinder heads decked by West Coast Cylinder Heads; it was merely a matter of shaving a little off the bottom. The heads are filled with stock LS7 titanium intake valves and sodium-filled exhaust valves.

Interestingly, the changeover to E85 was relatively simple. The factory fuel lines were sufficient, so that left only two necessary upgrades: the addition of alcohol-compatible fuel injectors—65-lbs/hr units from F.A.S.T.—and an engine controller recalibration. Finishing details included a F.A.S.T. LSXR 102-mm intake manifold, billet aluminum fuel rails and a Nick Williams 102-mm throttle body.

With the latest round of mods completed—including upgrading the Z06’s original dry sump-style oiling system to the new, larger capacity (10.5-quart) system—Harding had the E85-burning Z06 strapped onto Katech’s chassis dyno. It registered 568 rear-wheel horsepower and 529 lbs-ft of torque, or about 650 horsepower and 585 lbs-ft of torque at the flywheel. That 145-horsepower leap over the stock 505 rating is on the high side of what a bolt-on blower would deliver. What makes the achievement even more eyebrow-raising is the fact that it was achieved with no increase in displacement—the easiest path to adding naturally aspirated horses.

Harding can switch back to 93-octane gasoline with a quick engine computer calibration change made via laptop. GM’s factory FlexFuel vehicles have the ability to run any blend of E85 and gasoline, but the Z06’s controller does not have the hardware to calculate that, so the tank must be run down to empty before switching fuels.

Supporting the 650-horsepower engine is the stock 6-speed manual transmission, but the clutch is an Exedy twin-disc setup and the transaxle was upgraded with the stronger axle shafts that debuted on the ’08 Z06. There’s also a Dewitts high-capacity, racing-style radiator under the hood.

When it comes to reining in all that horsepower, Harding’s car relies on a set of enormous Brembo Gran Turismo brakes, featuring two-piece slotted 15-inch rotors and six-piston calipers in the front; 13.6-inch rotors are clamped by four-piston calipers in the rear. He uses Ferodo FM1000 brake pads on the street and Ferodo DS3000 pucks on the track. In either setting, the brakes deliver exceptional stopping power.

Despite their increased size, the Brembo brakes are lighter than stock Z06 brakes. This was no accident: Harding was looking to shed as much mass as possible. For example, he exchanged the stock battery for a lightweight racing version, a 15-pound Braille unit. Although the battery starts the car on the street just fine, leaving the lights or radio on for more than a few minutes sets off a search for jumper cables.

Also from Issue 63

  • Z07 vs. ZR1
  • Best Corvettes for $12K
  • 1957 Roadster
  • 800-bhp C5 Convertible
  • Tech: LS Strengthening
  • 1967 Coupe
  • Driver Training
  • 1969 Coupe
  • Race Report: Petit Le Mans
  • How-To: Radiator Removal
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