Drivability
Because an engine-driven supercharger is always “on,” it tends to give a street-driven vehicle an abundance of off-the-line/low-speed pull; to the point where it is difficult to manage part-throttle driving in some instances, as tire spin becomes an issue. The higher-RPM power application of turbo systems typically makes them more tractable at low speeds. The enthusiast wishing for supremacy off the line at stoplights with the instant application of full boost will probably enjoy a supercharger; while the enthusiast seeking a wider performance range will likely find a turbo system more rewarding.
Modern Roots and screw-type superchargers make excellent choices for street-driven performance vehicles, as they deliver instant power at low speeds. They’re also quieter and offer greater drivability than ever before. And when compared to custom or bolt-on turbo kits, they are very cost effective.
Noise
Generally speaking, the compressors of most supercharger and turbocharger systems are very quiet these days. Turbos are essentially silent until they start spinning at high RPM, and the same is true for most Roots/screw-type blowers. Centrifugal superchargers are much quieter than they used to be, but at idle, they’re not as quiet as turbos or Roots/screw-type superchargers.
Tuning
There’s no real advantage between tuning a supercharged or turbocharged engine, as the need to maintain an adequate air/fuel ratio and optimal spark to avoid detonation is paramount with both methods. Both types of systems have unique needs for delivering safe, optimal performance, but the basic approach to tuning is similar. There’s no clear advantage to either system.
Maintenance and Reliability
When installed and used properly, supercharger and turbocharger kits are very reliable with the compressors for both lubricated with engine oil, although some Roots/screw-type blowers feature self-contained lubrication systems. Over time, the drive belt for a supercharger must be inspected just like the engine’s standard accessory belt, and after a few years, the compressor may require an inspection to ensure the tolerances and clearances are within specification limits for the rotors. Turbochargers are very susceptible to heat, and even with adequate lubrication, the internal seals and turbine can wear and allow oil blowby. This requires the turbo to be rebuilt.
System Cost
Because of a myriad of extra equipment (from the wastegate to the exhaust manifolds), turbocharger bolt-on kits generally cost two to three times more than supercharger kits. Additionally, turbocharger systems generally take longer to install than supercharger kits. This adds up when outsourcing the project to a professional shop.
A couple of the biggest advantages of a supercharger for a primarily street-driven vehicle is comparatively easy installation and a lower labor investment. Bolt-on kits (particularly Roots/screw-type systems that essentially swap out the original intake manifold) can be installed relatively quickly with little impact on the rest of the vehicle’s components or systems. The quicker the installation, the lower the labor cost at a professional shop.
Installation Impact on the Vehicle
Assuming all turbocharger and supercharger systems employ an intercooler, the Roots/screw-type supercharger systems generally require the fewest compromises and/or fabrication modifications during installation. Because they install in place of the intake manifold, few changes are required at the front of the engine or in the engine compartment. Consequently, they offer the most integrated, factory-looking appearance under the hood. Centrifugal superchargers require a mounting bracket on the front of the engine that can require moderate modification, removal, or relocation of factory components.
With bolt-on turbocharger systems, the installation of the exhaust manifolds, turbochargers, and associated plumbing typically require considerably more fabrication, modification, and relocation of stock parts than supercharger systems. An intercooled turbo system can also take up more real estate under the hood, particularly when using larger turbochargers. That can induce a number of fitment challenges that require additional fabrication to overcome.
Installation Cost
Again, because of the extra equipment associated with them, turbocharger kits are generally more time consuming to install, and therefore, there are more labor costs.
So, while a turbo kit offers greater performance potential, the cost involved with this investment may steer some toward a supercharger. In fact, there are other factors to consider before ordering a system for your car.
For one, the tight confines of the engine compartments in Corvettes, Camaros/Firebirds, and GTOs/Monaros make packaging and installing a turbo kit very difficult. This not only makes the installation a painstaking and difficult procedure but can make future servicing all but impossible without an extensive teardown of the vehicle’s front end.
There is more room in the engine compartments of full-size trucks, SUVs, and TrailBlazer SSs; but stuffing a turbo system can be a challenge in a regular street car.
My opinion is that turbocharging is great for vehicles destined to spend equal time on the street and strip; but for typical, street-driven vehicles, a supercharger system is the easier and more economical method to build power. Many tuners and manufacturers that fall on the turbo side of the argument will undoubtedly disagree; but when it comes to bolt-on, forced-induction kits, superchargers are easier and cheaper to implement with less maintenance.
Understanding Boost (Including PSI Versus Bar)
Whether it is a supercharger or a turbocharger system, the measure of pressurized air fed into the engine is referred to as “boost.” It is the difference between the ambient air pressure and the increased air pressure that the boost-producing device generates at the intake manifold. Boost is the opposite of vacuum, which is what a nonboosted engine makes during normal operation.
When an engine isn’t running, it generates no vacuum or boost (negative pressure), meaning the pressure in the intake manifold is the same as the ambient air pressure: about 14.7 pounds per square inch (psi). At idle and low-throttle conditions, an engine generates vacuum, indicating the pressure in the intake manifold is lower than the ambient pressure.
In a supercharged or a turbocharged engine, boost is created as more throttle is applied and the boost-generating device forces air into the intake manifold at a higher pressure than ambient (positive) pressure. The air pressure at the intake manifold swings from negative to positive; that’s why high-performance boost gauges indicate both vacuum and boost measurements.
Boost is generated when the supercharger or the turbocharger creates air pressure greater than ambient when it is introduced to the engine (at the throttle body). Supercharged engines generate a small amount of boost whenever the engine is running, even at idle. Turbocharged engines require higher RPM to generate boost.
In North America, boost is generally measured in PSI, while bar is more common in other countries. When measuring in psi, the ambient air pressure is regarded as the base, or 0 pounds of boost. The positive pressure builds on that base with 1 pound of boost indicating 1 psi greater than ambient pressure.
With bar measurements, bar is roughly the equivalent of ambient air pressure. Technically, 1 bar is equivalent to 14.7 psi, not 14.5 psi, but many enthusiasts equate it to the normal atmospheric pressure, so a 0.5-bar pressure reading is roughly 7.25 pounds of boost. A full, 1-bar reading would indicate 14.5 pounds of boost.
Drag Racing
Turbochargers are common among Outlaw-type drag racing classes,