All About Turbochargers – Part 2: Comparing Superchargers to Turbochargers
We talked about the basic ideas on how turbos work and what boost is. Now let’s compare turbos to Superchargers. We’ll look at the advantages of turbocharging over supercharging, and tell you why the centrifugal supercharger is not a turbo.
While they both boost and help your engine produce more power, there is a difference between a supercharger and a turbocharger. The basic and most obvious difference is how each drives its compressor. Let’s start with how a supercharger works.
A supercharger is a belt-driven forced-induction system that uses the engine’s crankshaft to drive its compressor lobes or the gearbox attached to the compressor wheel on centrifugal-style units. Inside the snout of the supercharger are gears that transfer the spin of one lobe to the other. It’s also where the supercharger gets its famous whine noise.
A roots-style supercharger uses twin straight compressor lobes.
The rotary screw (or Lysholm) uses a pair of twisted compressor lobes. The advantage of the rotary screw is that it exhibits internal compression, which is the ability of the device to compress air within the housing as it is moved through the device instead of relying upon resistance to flow downstream of the discharge to establish an increase of pressure.
A centrifugal supercharger looks like a turbocharger compressor with a box in the back where the turbine housing should be. A centrifugal supercharger uses a compressor wheel and compressor housing much like a turbocharger does, but instead of being driven by exhaust gasses like the turbo is, it’s driven by a gearbox and belt from the driveshaft, or sometimes a belt from the driveshaft to a transfer shaft pulley to another belt on that to the compressor pulley … but that’s complicated. This is also what makes it NOT a turbocharger at all. Because it is belt-driven, it is a supercharger just as much as the sky is permeable.
The advantage of superchargers is near-instant boost. Instead of waiting for the turbine to spool up the compressor wheel to create boost, a supercharger will typically start making boost in as little as 2,000 rpm. The centrifugal is an in-between when it comes to boost lag (the term for spool-up delay); however, it is more efficient at making boost and can potentially make more power. The advantage for the aftermarket for superchargers is that it is easier to get a supercharger 50-state legal. This is because the turbo can act like a giant heat sink that prevents the catalytic converter from heating up to proper temperature in order to clean the exhaust gasses.
On the other hand, the turbo’s advantage is efficiency. Instead of using a belt on the crank of the engine to turn a gearbox, thus robbing 10 to 20 horsepower, the turbo uses wasted gases from your engine to create boost that makes more horsepower and torque. Also, unlike superchargers, you can control the amount of boost the turbo creates by using a boost controller. We’ll go over boost controllers in part six. The supercharger is limited to how big of a pulley is used, and isn’t easily changed out.
Click “NEXT” below to learn about the individual components of the turbocharger system.