A supercharger is a device that, when installed into an internal combustion engine, compresses the intake air, forcing it into the combustion chamber. The compressed air becomes denser, which results in extra oxygen to the engine, thus increasing its power and torque. To keep it simple, imagine that it’s as if the engine’s displacement were increased while the supercharger is working; injecting compressed air into it.
Can a Supercharger Be Turned ON and OFF?
This is a question many people ask, maybe influenced by the movie industry and films like Mad Max. By the time Mad Max was released (1979), the answer was “no”. Like many things shown in movies, the switchable supercharger was faked for dramatic effect purposes. The only benefit of switchable superchargers is fuel economy: superchargers are powered by pulleys attached to the engine and drain some HP like any pulley-driven accessory.
The higher the RPMs, the more power is needed to drive the supercharger, which means more fuel consumption. In addition to this, as engines rev up and superchargers build more and more HP, the engine’s fuel consumption increases, which it’s not good for Max. Fuel is a scarce resource in his post-apocalyptic world, and he can’t afford to run his powerful “Pursuit Special” always supercharged.
Back to reality, in 2021, some superchargers can be turned ON and OFF. Everything started in the early 80s with twin-charging technology; a combination of the best of both worlds: a small supercharger to add boost to the engine at low RPMs until the turbocharger kicks in. Once the turbocharger has been activated, the supercharger is deactivated.
Like many innovations developed for race cars, the twin-charging technology came to streetcars about 15 years ago. Some modern factory supercharged vehicles come with compressors that are automatically switched by the engine’s ECU depending on the circumstances; for example, when the engine is idling, the supercharger gets disengaged. A strange model is the Toyota Previa minivan, which comes with a switchable supercharger, a weird feature for a utility vehicle.
These superchargers are engaged and disengaged thanks to a clutch and an air release valve among other things. A lot of enthusiasts and tuners benefited from this technology to fulfill their dream of being able to engage and disengage their car’s superchargers like in the movies. In addition to all this, there are some manufacturers like Eaton that sell aftermarket superchargers that can be switched ON and OFF thanks to a strong electrical clutch.
Some users say that they can improve the fuel economy by 15% while they are driving their car with the supercharger disengaged. Being able to drive your car with your supercharger disengaged can be useful to save gas on long trips while you are driving at legal speed limits, for example.
Does a Supercharger Need an Intercooler?
It depends on the type and design of the supercharger. Traditional superchargers, like the Roots and the twin-screw, usually have built-in intercoolers and/or work below 10psi. These kind of superchargers usually come with a built-in intercooler. Besides, in the range of 6-7 PSI that is the boost that these superchargers usually deliver without an external intercooler, it is completely safe and pretty effective.
At these boost levels; adding an external inter-cooler can be helpful to gain some additional HP. However, there are some considerations to make: the piping needs to be installed far from the heat, it has to be smooth avoiding sharp bends, and it should be as short as possible.
Centrifugal superchargers deliver around 15+ PSI. Some models can deliver peaks of 21 PSI. They work similarly to a turbocharger but they are not driven by the exhaust gases but by a pulley. These kind of superchargers need an inter-cooler because they lack a built-in inter-cooler and because they compress the air so much that the air temperature gets too hot to be safely induced to the engine.
Can You Turn Up a Supercharger?
Yes, you can. The idea of turning up a supercharger is to get more boost from it – more boost means more HP -. As a supercharger spins, it compresses the air and generates boost pressure. The most usual way of turning up a supercharger is to swap the lower crank pulley for a larger one or to swap the upper pulley on the supercharger for a smaller one.
Doing this will increase the rotation speed of the supercharger; generating more boost. It’s a simple mod and there are plenty of kits available for cars that are factory-supercharged on the market. There are also pulley kits for aftermarket superchargers, and if you can’t find a kit for your specific model, you can always find a company selling a custom-made pulley. There are other ways to get more boost from a supercharger, but they are more complex. I’m going to tell you some of the most interesting ways to do it below.
How To Get More Power Out of a Supercharger
If you want to get even more power from your supercharger without replacing it for a larger one, some improvements can be made, depending once again on the unit’s model.
Sometimes it is possible to change the drive gear ratio to make the compressor spin faster.
There are many aftermarket gear kits for different models and makes of superchargers. This improvement should be made by a professional, as it requires opening the unit to replace the gears. This mod can be done in Roots, twin-screw and, centrifugal superchargers.
Some tweaks can be made to positive displacement superchargers (Roots and twin-screw) like increasing the diameter of the throttle body, porting the supercharger’s inlet, adding a spacer between the supercharger’s body and the engine’s intake manifold, and/or installing a modified supercharger’s air intake. These improvements combined help to optimize the supercharger’s airflow and to increase its boost altogether, and you can expect a power gain of around 20%.
Centrifugal superchargers can also be modified. It’s possible to modify the case of a centrifugal supercharger to install a bigger core with bigger propellers. Centrifugal superchargers don’t have a wastegate like turbochargers, but they have blow-off valves. It’s possible to replace the blow-off springs with a set of stiffer springs to delay the opening of the valve and to get higher peaks of boost.
Warning Signs of a Bad Supercharger
Superchargers, like any other mechanical part, can break, damage, or wear out. There are some signs that any supercharger user should be aware of.
- Power loss or a lag feeling when accelerating.
- Strange noises coming from the supercharger.
- Squeaking sounds from the drive pulley.
- Clicking noises at idling that stop at high RPMs.
- The supercharger is whistling louder than usual.
- Whining sounds coming from the supercharger.
- Oil leakages around the supercharger.
You should take your car to the shop as soon as you notice any of these symptoms. Superchargers are tough, but it’s better to be safe than sorry.