We sit down with TTS Performance to talk all things superchargers as this guide helps you understand how they work compared to a turbo; plus, the things you should consider before upgrading to one.
Guide from Fast Car.
What is a supercharger and what does it do?
To improve the performance of an engine it needs more fuel and air. A supercharger is an air compressor that supplies this extra air at more than atmospheric pressure. A supercharger needs power to work. Normally the term supercharger is used for a unit that is mechanically driven from the crank, but if the power is provided by a turbine, the supercharger is known as a turbocharger.
Are all superchargers the same?
There are two main types of superchargers: Centrifugal and Positive Displacement. Centrifugal superchargers deliver increased pressure with increased engine speed. They work by accelerating the inlet air by giving it a very high speed from a compressor wheel known as an impeller. This speed energy is then exchanged to pressure when the air is slowed down in the diffusor inside the compressor housing. Positive Displacement blowers deliver a certain amount of air per-engine revolution, independent of speed.
There are three major types of Positive Displacement supercharger: Roots, Twin-Screw and Scroll – also known as G-Lader.
What are superchargers made of?
The Centrifugal Supercharger typically has an internal ratio step-up gear that gives the impeller a much higher speed than the input drive. In general, the efficiency of the compression increases with higher impeller speeds. Step-up gearbox based on gear sprockets or belts are limited in speed and hence efficiency, whereas traction drives, such as the Rotrex, can reach extreme speeds far above gear and belt-based boxes. Positive Displacement superchargers typically have two internal counter rotating rotors that are synchronized with a very small clearance. This makes them sensitive to debris and heat expansion.
Why is a supercharger a good route to gain power?
There are several ways to improve engine power, but basically, it’s all about moving greater volumes of air in and out of the engine.
The most obvious way is to increase engine capacity, but with focus on emissions and engine size this is not beneficial.
Increasing engine speed also dictates expensive and complicated cam timing to avoid unwanted emissions. Colder intake air and higher volumetric efficiency increase power but with limited effect. Boosting, therefore, is the best way to improve power when emissions and power are key. No other alternative gives so much power for the money. When boosting is used, the performance limit is based on the engine internals with more than 100% gains often seen when the engine is properly prepared.
What is the difference between a supercharger and a turbo?
This could indicate that the turbo is driven for free and the supercharger steals energy from the crank that should have ended up at the wheels. However, this is not the full story.
The main part of the exhaust energy is the high pressure in the exhaust ports that creates a pressure difference over the turbine wheel of the turbocharger. The backpressure in the downpipe dramatically reduces the Mean Effective Pressure on the pistons. This, combined with the limitation in efficiency of the turbine, reduces torque. The reduction is in the same order as the power needed to drive the mechanical supercharger. Also, because the turbocharger traps hot residual exhaust gas in the combustion chamber the temperature of the fresh fuel/air mix is increased. Therefore, the mixture in the turbo engine must be richer and the ignition timing lower. Both reduce fuel economy and performance. Several comparisons between turbochargers and efficient superchargers show almost identical performance and consumption results. With regards to emissions, the supercharger has advantages due to freedom in design of the exhaust system and less heat inertia.
How important is it to get the right type of supercharger for your application?
Getting the right type and size of supercharger is very important as each has different attributes. If constant and high-end torque is required, the centrifugal type is ideal as it features a very smooth power increase and low stress on the transmission. In a heavy car with a small engine, more torque is needed at low engine rpm, so a Positive Displacement is the preferred choice.
Efficiency during compression of the air is also very important because more power can go to the crank and the size of the intercooler can be reduced if the efficiency is high. Low temperature of the inlet air is also important for engine reliability and performance. In general, the centrifugal supercharger has better efficiency than all other types of pump.
What are the main limitations or downsides of superchargers?
The physical size of the blower and additional items such as intercoolers and pipework are always an issue because installation into increasingly cramped engine compartments makes fitment more difficult. Also, noise from the air compression is very dominant in a Positive Displacement supercharger, however, the Centrifugal blower is quiet, with Rotrex being the only unit that is essentially silent even at idle.
What other mods should you consider when installing a supercharger?
If the boost pressure from the installed kit exceeds 5 psi an intercooler is needed to reduce inlet air temperature.
Depending on the power gain, the exhaust system should be modified to reduce backpressure. Normally the standard cams are fine for lower boost, but performance cams are available if more power is needed.
As with any power upgrades, careful remapping and precise ignition and fuelling is a must for a successful installation. Finally, depending on the target level of power increase, the engine internals may also need to be upgraded and compression lowered according to needs.
Why don’t more car manufacturers use supercharger technology?
It’s no secret that the turbo is the dominant boosting device between car manufacturers. The turbocharger manufacturers can support the OEM with implementation and low prices.
The very positive feedback from aftermarket supercharged cars can improve the supercharger market share. When car manufacturers realise it’s possible to get high efficiency, low noise at a good price, more cars will be supplied with superchargers. New stricter emissions rules will also push in that direction because the catalyst will have a shorter heat-up time. Hybrid solutions with 48V power supply will add torque at low engine rpm and open for a solution with an efficient centrifugal compressor like the Rotrex. The high-volume car industry is very conservative towards new technology because of the economic risk, so the implementation will take time.
Other than ensuring you get the right one for your application, what are the most important things to look out for when buying a supercharger?
When buying a supercharger, it’s very important that reliability and factory back-up is good. If the supercharger is sold to the OE market the quality, reliability and back-up is seriously controlled by the manufacturer and you can be sure that this will not cause problems.
Many supercharger manufacturers sell their products to the motorsport market. This market takes the units to the extreme and if the chargers can handle this treatment, they are probably good enough for the road.
The supercharger is the most expensive part of the kit so the unit price will heavily influence the kit price. If the installation kit is simple, however, because the supercharger is easy to install, a higher unit price is acceptable.