CarVerse Tech: Turbocharging vs. Supercharging

Monday, November 16th, 2015

Okay boys and girls, it is time for some Engine 101. A gas engine creates power by igniting a mixture of gasoline and air inside the cylinder (a diesel combusts fuel by compressing the fuel/air mixture). The resulting explosion forces the piston down and turns the crankshaft. This spinning force is then sent through the transmission, to the drive wheels. If you want to create more power, you can feed a higher volume of air and fuel into the cylinder, which will cause a more powerful explosion. The air acts as a catalyst for the explosion, and to get more of it, you can use a forced induction system like a turbo or a supercharger. What’s the difference? Glad you asked…

Turbo 101

A turbo is an air pump that forces lots of air into the intake system. It is typically mounted near the exhaust manifold, where it uses the high-pressure exhaust gasses coming out of the motor, to spin an impeller at a very high rate of speed. Opposite that turbine is a much larger turbine that acts as a fan, forcing fresh air back into the intake. To optimize performance, the air is often routed to an intercooler, which cools the air before it goes into the engine. Naturally, cold air contains more oxygen, and that helps to burn more of the fuel during the combustion cycle.

Since a turbocharger uses the exhaust to force more air into the engine, it does not require any power from the engine in order to work. The downside is that the turbine can only spin as fast as the engine is turning. At low RPM, the exhaust gas is not flowing out of the engine fast enough for the turbo to create much boost. As the RPMs climb, the turbo can spin much faster, which forces more air into the cylinder, creating an increase in horsepower. When you first step on the gas, the engine will respond as if it did not have a turbo. Then, as the RPMs above 2500-3000, the turbo will “kick in”, giving you an instant shot of power. This delay in power delivery is commonly referred to as ‘turbo lag’.

To overcome turbo lag, most automakers now use multi-geometry turbos. Commonly referred to as twin-scroll turbos, these clever little air pumps use a small turbine to create boost at low RPMs, and a larger turbine to create even more power as the RPMs climb. Thanks to this inventive technology, cars like the 2015 Ford Mustang EcoBoost can make a staggering 310-hp / 320 ft-lb of torque from a tiny 2.3L 4-cylinder.

Supercharger 101

Like a turbo, a supercharger produces power by forcing a large volume of air into the engine. The difference is, a supercharger uses engine power to spin the turbines inside. Typically, a pulley on the front of the blower is connected to the engine using a drive belt. This allows the boost from the supercharger to be available almost immediately. In the case of the 2015 Dodge Challenger Hellcat, it takes 80-hp just to spin the massive 2.4L IMI supercharger. This state-of-the-art blower creates 11.6 psi of boost, and this helps the 6.2L Hemi V8 to produce a whopping 707-hp and 650 lb-ft of torque.

There are a few different types of superchargers available on the market such as twin-screw, positive, roots, centrifugal and a few others. Centrifigual superchargers are the easiest to spot as they look like a turbocharger hanging off the engine near the accessories. These are driven by the same pulley setup as the other types of superchargers; however the other types will typically replace the intake manifold on top of the engine.