Turbocharger vs Supercharger - Part 2 of 4

Centrifugal Supercharger (Ex: Vortech)
Vortech Engineering, notorious in the domestic centrifugal supercharger market, now has numerous offerings in the import market and is the authority on this type of supercharger. Centrifugal superchargers are easy to spot because they bear a striking similarity to the familiar snail-like shape of turbochargers. Flip a centrifugal supercharger over though, and you'll see the belt driven pulley attached to the backside. With the use of a longer engine belt, the Vortech's pulley is driven by the crankshaft's turning power, the same as an alternator or water pump pulley. Connected internally to the rear pulley, the Vortech's compressor wheel spins with the engine, creating boost.

This cutaway Vortech supercharger
shows off the internal step-up gearing used
to spin the compressor up to 60,000RPM.

Because the engine belt drives it, the Vortech's pulley will always spin proportionally to the engine RPM. The problem with this is, even 9,000RPM is not enough spin to generate any usable boost. Vortech gets around this problem by utilizing internal step-up gearing that increases the speed of the compressor blades to nearly ten times the speed of the engine. Capable of just under 60,000rpm, the Vortech's compressor generates significant boost at high engine RPM's, and can generate even more boost by changing to a smaller pulley, which will run the Vortech at a faster speed. At low engine RPM's, the stepper gears can only do so much, spinning the Vortech at less than optimal speeds and generating minimal boost.

The stock STi turbo (L) displays its outlet,
where you can make out the internal wastegate and turbine wheel.
The Vortech s/c (R) shows off its drive pulley mechanism.

Because the centrifugal supercharger ramps up boost in relation to engine RPM, its powerband increases mostly on the top end. A centrifugal unit is best suited to cars that need to be at high RPM's anyways, such as Honda's S2000, and cars that naturally have low-end power to compensate, such as the 3.5L Nissan 350Z.

60,000RPM is a lofty speed for any piece of machinery and friction fatigue could be a serious issue. The same oil that coats the engine lubricates the Vortech internally, but don't worry, you'll end up changing your oil in the same exact way you always would. The catch is that during installation you'll have to drill a hole into your oil pan or crankcase in order to run oil lines to the Vortech. The Vortech is designed to be installed in about a day, but if drilling into your car doesn't sound like your idea of fun, look up and factor in the cost of professional installation. Afterwards, the kit will prove itself to be reliable and should require no more maintenance than your standard 350Z.

The engine bay of a Vortech'd 350Z.
In the lower right corner is the belt and
pulley system used to drive the supercharger.

Vortech's supercharger kits are sold complete, and include fuel upgrades, ECU control, and intercooling. A byproduct of compressing air is that the air gets heated after compression, and as any cold-air intake owner knows, colder air is better for the sake of both power and reliability. This is where the concept of intercooling comes into play. An intercooler is essentially a radiator for forced induction, allowing the compressed air to cool before entering the engine. Although not required, an intercooler is a highly recommended part of any forced induction setup, turbo or supercharger. Vortech's 350Z kit uses the very popular front-mount intercooler setup, which uses airflow through the front bumper to cool off boosted air before it enters the engine.