2004 Chevrolet Corvette Z06 - Fine Whine

Tony Demambro Experiences The Ups And Downs Of Supercharging With His '04 Z06

Wayne Ellwood Jun 1, 2009 0 Comment(s)
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Alex Olivera of Real Pinstriping applied a thin line on each of the splitters, a flourish in the rear bumper (shown), and another design on the console.

DeMambro began looking at superchargers, eventually settling on a Blowerworks system designed by noted forced-induction expert Greg Carroll. The system was gaseous intercooled, solidly built, and came with a water/alcohol-injection system to control detonation. DeMambro enlisted Harbour Chevrolet's Dave Belmore, a technician with considerable performance experience, to perform the installation.

The job went smoothly, but the first dyno run was a huge disappointment-only 425 hp at the rear wheels. Belmore adjusted the fuel mix and timing and, with a little fiddling, the car pulled nearly 500 rwhp. At the dragstrip, the blown Z ran 12.4s at 124 mph on street tires, but during one of the runs, it let out a big puff of white smoke. Later, it was determined that the dipstick had been pushed out, and oil had sprayed everywhere. After a few more runs, the clutch overheated and wouldn't disengage.

In retrospect, DeMambro figures this was probably the beginning of the end of the first engine. Still, the car seemed to be running well, and it wasn't raced again for the rest of the year. The weak links were upgraded; the clutch was changed to a Centerforce unit, and the stock tires were replaced with Nitto NT555R performance rubber.

Then, while pulling out of a gas station, DeMambro noticed a huge cloud of white smoke billowing from the engine compartment. Checking the engine, it became clear that oil was coming out of the oil-filler cap and covering the hot exhaust system. Somehow the oiling system was getting pressurized, possibly the result of a PCV valve that had been installed backwards.

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By this time, DeMambro was coming to the conclusion that something else wasn't quite right. Sure enough, during a compression check, it was discovered that the No. 7 cylinder was down to 75 psi, instead of the normal 150 psi. DeMambro realized that his decision not to upgrade the stock pistons, rods, and crank at the time of the blower install was finally coming back to haunt him. It was time to pull the engine and see what was going on.

When he saw the pistons, it became clear what had happened. The oil-ring lands in two of the eight cylinders had been partially blown off. Hence, the drop in compression. However, since the block and heads weren't damaged, DeMambro made the decision to update the bottom-end internals instead of replacing the entire motor. It was cheaper, after all, and it addressed the underlying problem.

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The stock crank was deemed adequate, but Eagle H-beam forged rods and Mahle forged pistons (complete with valve reliefs to lower the compression ratio) were subbed in for their factory counterparts. The head bolts were replaced with studs, the exhaust ports were port-matched, and the cam was updated with a GMPP unit boasting slightly more duration and lift. All of the work-including the final balancing-was performed at All Cape Machine in Hyannis.

This time, DeMambro turned to Dez Racing in Seekonk for tuning. After a disappointing initial dyno pull of 325 rwhp was traced to fouled plugs, a backup run put the tally at 423 rwhp-better, but far off the car's previous best of almost 500.

Dez Racing owner-operator Don Kinder deduced that DeMambro's engine modifications had actually lowered the LS6's compression too much. He suggested lowering the timing, which would allow the engine to safely accept 10-15 psi of boost. This, in his opinion, would really allow the supercharger to shine.

Kinder obtained new, smaller pulleys to generate the extra boost. Because the standard six-rib belt and accessory drive were designed for no more than 10 psi, Greg Carroll recommended a new eight-rib unit along with a stronger tensioner to reduce belt slippage.

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