Here's How to Choose Between Superchargers
The core idea of a supercharger is simple: it makes intake air more dense, allowing more air in a small space and, therefore, more fuel. That gives you a lot more power. But the reality isn’t that clean: there are a lot of different, complicated ways to do that job. These are the differences you need to know, courtesy of Jason Fenske from Engineering Explained.
For both a roots and a twin-screw supercharger, the layout is easy to understand and mostly the same for both. Air comes in through the intake, passes through the throttle body, and then into the belt-driven supercharger. Then it’s sent through an intercooler before passing through the combustion chamber and out through the exhaust.
The biggest difference, though, is what’s going on inside the supercharger itself. Though only one has “twin” in the name, both styles involve two rotors. But in a roots supercharger, two identical rotors rotate away from each other, quickly forcing more air into the engine than it can take at once. This causes positive pressure to build in the manifold, compressing the air. In a twin-screw style supercharger, the two rotors are designed to mesh with one another and compress the air forced between them. So while they’re both similar in design, twin-screw superchargers compress the air directly while roots superchargers create pressure in the manifold that compresses the air.
Both of these offer a wide torque curve, though there are different advantages. Twin-screw superchargers are slightly more efficient, but roots superchargers are getting better. Both of them are bulky and can be difficult to package.
But there is another option. Centrifugal superchargers—which include belt-driven and electric superchargers of the kind—use an impeller to pull in air. By pulling in air faster than the engine can use it, it also causes positive pressure to build in the manifold, compressing the intake air. Much like roots and twin-screw superchargers, the air typically also passes through an intercooler to cool it down, making it denser.
The downside of this design is that, if you’re driving it off of the engine, you need serious revs to get the supercharger’s full torque load. Even if you gear it to multiply the speed, you’re not getting peak power from the supercharger until peak RPM. The upside, though, is that centrifugal superchargers are easier to package and very efficient.
And with an electric centrifugal supercharger, you can solve the biggest downside. Because an electric supercharger isn’t powered directly by the engine, you can spin the impeller to peak speed whenever you have power in the battery. That means peak power from the supercharger is available at any RPM, so long as you have energy. Unfortunately, they also require more expensive 48-volt electrical systems and they’re very complicated.
So there’s no perfect supercharger. But depending on what you need, what you can fit, and what you can afford, now you know which style works best.
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