Turbocharger vs Supercharger - Part 4 of 4

Positive Displacement/Roots Supercharger (Ex:Stillen)
Used by the Chevy Cobalt, Comptech's NSX kit and Jackson Racing's infamous Honda kits, the positive displacement supercharger is the third most popularly used aftermarket forced induction design. Identified by its chunky, ribbed design, the positive displacement supercharger, commonly referred to as the Roots-type blower, is represented in the 350Z arena by Stillen.

The intercooler look-like in the front bumper
is actually the heat exchanger for
the Stillen air-to-water intercooler setup.
This unit chills down the water that
cools the air intake charge.
Also note the bulge in the hood,
which is necessary to clear the blower unit.

Stillen's supercharger is belt and pulley driven, much like Vortech's centrifugal unit. The difference is that intake air entering the Stillen blower isn't actually compressed, rather it's gathered, funneled and pushed into the engine, generating positive pressure, i.e. boost, as the air backs up in the intake manifold. Stillen sells kits up to Stage 4, with Stage 3 and Stage 4 utilizing smaller pulleys that allow the blower unit to spin faster, pushing more air and generating more boost. The Stillen Stage 2 kit utilizes an air-to-water intercooler system, which consists of a front-mount radiator that runs coolant piping through the air gathered by the blower unit, cooling it without having to fill the snakelike piping of a front-mount air-to-air intercooler setup.

This is the underside of the Stillen blower;
dead center is the exit for the air
funneled by the twin rotors.
To the left is the black actuator,
which controls the built-in bypass valve.

Because the Stillen blower doesn't use any step-up gearing and doesn't need to spin very quickly, the twin internal rotors always turn at the same RPM as the engine. This means that the Stillen unit will always shovel the same amount of air relative to the engine, even low in the rev range. This kind of instant, low RPM response means that the positive displacement supercharger lives up to its literal name, making the powerband feel like it came from a larger displacement engine.

The Stillen setup makes the 350Z feel more like a V8 than a V6, producing large amounts of low and mid-range power instead of focusing solely on the top end. This sort of powerband also matches well with small displacement engines that lack torque, such as Honda's K-series engines. Focusing on street use, Steve Millen told us that his tuning principle was to maintain CARB exemption as well as increase the powerband in the area where a street car will see the most time.

Once installed, the Stillen blower replaces
the upper intake plenum and rests right on top of the 350Z's engine.

In fact, as one of the simplest forced induction designs to install, the Stillen kit doesn't require any oil pan replacement or tapping and the Eaton-supplied blower is self-contained and retains OEM-level reliability. An optional warranty is even offered by Stillen on its Stage 2 kit. All engine tuning has been completed in-house and there is no provision for the end consumer to do any tweaking or tuning of his own. The only downside to the Stillen unit is that due to the physical size of the blower, the stock hood cannot be used anymore. Stillen sells various fiberglass and carbon fiber replacement hoods for use with its blower kit, a popular upgrade anyways for many Z owners.

With so many paths to the nirvana of power, one can easily get confused. By balancing cost, maintenance, power output, the shape of the torque curve, emissions exemption and engine tuning, you can decide which path is the correct one for you. Each will deliver big power increases over stock and can shred tires with ease. Take a look at our dyno charts and weigh your options, it's just a matter of finding what fits your needs and your driving style.