Turbo Technology C5 Twin-Turbo Kit - Two Turbos, No Lagging

The turbochargers in the kit are Garrett T28 units with a T3 compressor. The T28 turbo is approximately the same size as the compact Garrett T25, yet flows more air. This means the turbo still delivers the lightning-quick spool-up of a compact turbo, but makes more boost. Turbo Technology tells us they plan to offer a ball-bearing upgrade soon.

The air-to-air intercoolers included with the kit are Spearco units. Turbo Technology modifies the inlets and outlets so that tubing leading to and away from the intercooler fits within the confines of the C5's frontend. Spearco intercoolers have a bar-and-plate core design, rather than a conventional, radiator-style tube-and-fin design.

This unique component is where pressurized air from both turbochargers meets and heads into the engine (see arrows).The circular provisions are mounting locations for the necessary blow-off valves.

A foundry near Turbo Technology's Tacoma, WA, headquarters produces the thick, heat-resistant cast-iron exhaust manifolds for the C5 kit. Turbo Technology then covers them in Ceramachrome: A high-temperature coating that gives the manifolds a polished appearance.

The first step in installing the turbo kit is the removal of the Corvette's front fascia. Future restorers take note of the crayon markings on the outside of the black plastic inner wheelhouse.

With the Vette's nose removed, the intercoolers are bolted into place beneath the headlamps. On the passenger side of the car, the horns need to be moved to accommodate one of the intercoolers.

The exhaust system must be disconnected, and the original exhaust manifolds removed. They'll be replaced with the Turbo Technology manifolds. Also, the alternator (seen here at right of the exhaust manifold) must be removed and trimmed.

This photo provides a good look at how the turbo mounts to the exhaust manifold. And though it would easier to mount the turbo and slip the assembly into place as a single unit, the limited space beneath the Corvette prevents this. After several wasted minutes of contortion and cursing, our installer found this out the hard way (and learned something about reading the supplied directions).

Oil drain lines must be fitted from the turbochargers to the oil pan. This means drilling holes into the oil pan. Needless to say, it's a procedure that needs to be done right the first time.

One of the tricks when it comes to tapping the oil pan holes is to slather the tap with grease. Metal shavings stick to the grease and come out of the tap, rather than into the oil pan.

Still, it's important to change the oil soon after the project is completed, so that any errant shavings are flushed out of the pan.

The blow-off valves utilized in the Turbo Technology kit are Super Sequential units from HKS. Blow-off valves are necessary to provide pressure relief when the throttle closes, thereby preventing compressor surge or boost leak. The Super Sequential valves are unique in that, unlike conventional "push" valves, they are "pull" valves. Each has a small primary valve for quick activation and a larger secondary valve for additional pressure relief. Blow-off valves are responsible for that characteristic "whoosh" sound heard from so many turbo systems, including the C5 kit.

As the kit comes together, it's clear to see the routing of the system within the Corvette's front bumper area. Air exiting the intercoolers and feeding into the "Y"-pipe is headed into the engine. On this six-speed-equipped car, it was necessary to adjust the mounting position of the transmission cooler to accommodate the Y-pipe.

The pressurized air in the Y-pipe flows into the stock mass air meter, which is mounted to a cold air-style intake included with the kit.

To fit the driver-side turbo-to-intercooler pipe, the alternator has to be trimmed of one of its mounting tabs. A brace for the alternator is included with the kit to ensure the alternator remains securely mounted.