A high-compression (13.1:1) version of the LSX454 designed for drag racing, featuring a mechanical roller cam, high-rise intake, and more. It is capable of more than 750 hp.
Supercharging Versus Turbocharging
At their most basic, turbochargers and superchargers are air pumps but with different pumping characteristics. The turbocharger is an exhaust-driven pump that saps no engine power when not making boost. A supercharger is an engine-driven pump that is essentially another component on the accessory drive system and requires a modicum of power to drive, even when it’s not producing much or any boost.
The thermal efficiency, also known as adiabatic efficiency (the amount of combustion energy that is converted to power), is generally greater with a turbocharger system than a supercharger because it recycles a significant amount of exhaust energy to spin the compressor. That exhaust energy is lost to the exhaust system in normally aspirated and supercharged engines. That said, centrifugal and Lysholm (screw-type) superchargers can be up to 85-percent efficient, for comparable efficiency with a turbocharger.
In general terms, superchargers deliver greater power and torque at low- and mid-range RPM levels with nearly full boost available immediately at wide open throttle (WOT). A supercharger’s effectiveness tends to trail off at higher RPM, while turbochargers typically deliver their greatest power contribution at mid- to high-RPM levels, with boost building progressively in line with an increase of engine speed. Turbochargers are also very good at building mid-range torque, and when properly sized, can deliver excellent low-end power too.
There are a number of factors to consider before purchasing a bolt-on system. The performance requirements and engine demands for custom combinations and racing applications are different, but for the enthusiast seeking to add a forced-induction system to his or her vehicle, the following points are the most relevant.
Superchargers (particularly Roots and screw-type blowers) are excellent at delivering low-RPM power, as they are always making at least a minimal amount of boost when the engine is running. That’s because the supercharger is directly linked to the crankshaft via the drive belt. That connection also requires a small amount of horsepower to simply turn the supercharger.
Power Projections
Generally speaking, a supercharger will produce about 6 percent greater horsepower for every pound (0.07 bar) of boost, while a turbocharger will produce about 7 percent greater power for every pound. The turbo’s advantage there is due to the parasitic loss of the supercharger’s drive system. It simply costs some power for the crankshaft to drive the blower. The exhaust-driven turbocharger doesn’t have such a drag.
Turbochargers require no engine power to drive and, therefore, are considerably more efficient than an engine-driven supercharger. However, boost only occurs when the engine RPM rises. At low speeds, particularly off idle, the turbocharger provides no horsepower increase.
The advantage of turbocharging in a racing application is clearly illustrated in this partially constructed fourth-generation Firebird, as two very large turbochargers were adapted to an LS engine. Except for the older, “71”-series superchargers used in Top Fuel, Top Alcohol, and some Pro Mod–type drag racing classes, there aren’t Roots and screw-type superchargers that deliver the airflow of a pair of extra-large turbos. Even large centrifugal blowers are limited to only one per engine. With a pair of turbos, each driven by half of the cylinders, the only real limit is keeping the engine itself together under maximum boost.
Apart from the capacity to change the drive pulley on some superchargers, the output of a blower is pretty much determined by the size of the compressor. With a turbo system, a number of elements are easily manipulated to increase power. In fact, the almost-infinite adjustability of turbo systems is one of their primary appeals.
Performance Range
As noted earlier, superchargers (particularly Roots/screw types) generally deliver gobs of low-end power and become less efficient at higher RPM. The opposite is generally true for turbochargers; they tend to deliver their greatest performance as maximum boost is delivered with higher engine speed.
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
