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Turbocharger vs Supercharger

Which Is Right For You?

Text By Joey Leh, Photography by Staff, Courtesy of Manufacturer

Forget meth, blow, angel dust and smack, speed is the drug of choice for true connoisseurs. The only problem is, very few cars come from the factory with the sort of raw acceleration and "push you in the seat" power that you demand. Enter the aftermarket forced induction kit. Turbocharging and supercharging have existed for years, and ever since wheels have turned in anger, engines have been boosted.

One of the easiest and most cost effective ways to see horsepower gains of more than 30 percent on a stock engine, forced induction remains one of the most sought after upgrades on the market today. Intakes and cat-back exhaust systems are great ways to lay the foundation for big power, but they won't be able to do it alone. The majority of import engines are finely tuned from the factory, and only minimal gains will be found with bolt-ons. Plus, if you're looking to build a naturally aspirated monster, expensive individual throttle bodies and mucho aggressive camshafts will affect driveability so much, you'll wish you went with forced induction in the first place.

In fact, some of the most popular platforms of today were made that way because of the power potential that forced induction can offer. Just take a look at the Subaru WRX, Mitsubishi Lancer Evolution, Mazda RX-7 and the Nissan 240SX/SR20DET swap-these things can make power easy. If and when you do decide to get pressurized, you'll soon discover that there are more turbo and supercharger kit offerings than there are fingers to count with. The key is to figure out what you want from your car ahead of time and plan accordingly. Let 2NR be your guide.

The Basics
The first thing you'll need to know is that a supercharger and a turbocharger are pretty much the same thing. Both are essentially air pumps, cramming more air into the intake than an engine can suck in on its own. Boost, which is normally measured in pounds per square inch (psi) or bar (1 bar = 14.7psi), is the amount of air pressure that an engine will see over a naturally aspirated setup. The difference between the two chargers lies in the fact that turbochargers make boost through the spinning of a turbine wheel that is pushed by exhaust gases, while supercharger compressors are driven by a belt connected to the various pulleys on an engine's face. Because they are driven by different methods, turbos and superchargers make boost and power in different ways, giving potential buyers a different driving experience.

Although the basic principles can be applied to any platform, in this article we'll be using the Nissan 350Z as our example and will focus on the three main types of aftermarket forced induction kits, the centrifugal supercharger, the turbocharger, and the positive displacement/Roots supercharger.

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.

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.

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.

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.

Turbocharger (Ex: Greddy)
With a compressor design very similar in appearance to a centrifugal supercharger, a turbocharger could easily be mistaken at first for its pulley driven brother. The big difference is, turbochargers are driven by exhaust gases, not by belts and pulleys. Flip over a turbocharger and you'll see the cast turbo inlet and outlet, along with a wheel referred to as the turbine. From the exhaust ports, gases flow into exhaust manifolds that feed the turbocharger's inlet. As the gases flow from the inlet to the outlet port, they spin the turbine wheel as they rush through the turbo's hot side. This turbine wheel is connected by a shaft to the compressor wheel, which can spin up to 100,000RPM, generating some serious boost. Turbochargers were the magic behind the early 1980's Formula One racing machines, which developed more than 1000HP out of 1.5L engines.

In a supercharged and naturally aspirated car, exhaust gases are merely spit out the tailpipe, where in a turbo car, the otherwise wasted energy in the exhaust path is used to generate boost. Free of pulleys, belts and gears, turbochargers are much more efficient than superchargers, but much more complex as well.

To prevent too much boost from generating in the engine, turbo systems utilize a management system known as the wastegate. Internal and external wastegate designs exist and both accomplish the same task. A wastegate remains closed during initial use, using exhaust gases to increase pressure and build boost until the wastegate detects that the preset boost level has been reached. At that time, the wastegate opens to bleed off excess exhaust gases and continues to maintain the same boost level. With proper control of the wastegate, a turbo can be setup to generate boost as soon as it enters its boost threshold and can control boost to prevent an 80psi-induced detonation wave from smashing your engine to pieces.

The boost threshold, commonly and incorrectly referred to as "lag", is the RPM at which your engine generates enough exhaust flow to spin your turbo. Keeping the boost threshold low is the reason why stock WRX's use such tiny turbos, and big power with no regard for a low boost threshold is the reason why 1000whp Supra's regularly use snails the size of Texas.

Because the 350Z uses a "V" configuration six-cylinder engine, the most responsive turbo setup is to use two turbochargers and mount one on each side of the engine, using three cylinders to feed each turbo. GReddy's 350Z kit utilizes this twin-turbo design, and while the door to 600whp+ can be opened with this turbo system, installation and maintenance can be higher than that of a supercharger system. Already a tight engine bay, squeezing two exhaust manifolds, two external wastegates, two turbos, two intakes, intercooler piping and two downpipe elbows under the hood of a Z is not an easy task. On our own Projekt Z, the steering shaft and starter had to be temporarily removed in order to maneuver the turbos into place.

Also, because turbocharger systems reference their boost levels based on outside air conditions, care must be taken to ensure proper boost control under all driving conditions. Crawling through traffic on a sunny day and blasting along on a cold, rainy night are two completely different situations that can produce large differences in the amount of air a turbo machine ingests. The same precaution exists for taking a turbo car to different altitudes, making a good boost controller and proper engine tuning a must.

GReddy sells a well-designed electronic boost controller, a measure that can be taken against boost spikes and overboosting, allowing safer operation of a turbo system. A boost controller also has the ability to let an end user crank up the boost at the touch of a button, allowing nearly limitless power potential.

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.

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.

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.

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.

HOTBOX
Vortech Engineering
Oxnard
CA
8-05/-247-0226
www.vortechsuperchargers.com
GReddy
Stillen
3176 Airway
Costa Mesa
CA  92626
714-540-5566
www.stillen.com
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By Joey Leh
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