What's The Difference Between A Turbocharger And A Supercharger?
A turbocharger relies on a vehicles exhaust to spool up a turbine to power a compressor. The compressor then pulls in and feeds more air to an engine. On the other hand, a supercharger depends on the engine to rotate. It can be gear driven or belt driven, but the engine will power the unit.
From an efficiency standpoint, the turbocharger has an advantage. It takes wasted exhaust and turns it into something useful. Meanwhile, a supercharger won't do this and acts more like a naturally aspirated engine.
However, with a turbocharger comes lag. A supercharger doesn't rely on exhaust gas and power comes immediately. Superchargers can more easily be tuned to provide linear boost across the rpm range as well. Other downsides to a turbocharger include a lubrication requirement. A turbo requires engine oil lubrication, which is another demand on the engine. And as the turbo creates more heat, the oil will degrade quicker. For the record, some superchargers require engine oil lubrication as well, but it will never reach the more extreme temperatures that a turbo will.
This isn't to say a supercharger is perfect. A supercharger is literally taking power from the engine itself to make more power. Of course, the driver gains the power back, but it's not a very efficient process.
Which Is Better: Turbo- Or Supercharger?
Each can be used to increase power, fuel economy, or both, and each has pros and cons. Turbochargers capitalize on some of the "free" energy that would otherwise be completely lost in the exhaust. Driving the turbine does increase exhaust back pressure, which exerts some load on the engine, but the net loss tends to be less by comparison with the direct mechanical load that driving a supercharger involves (the biggest blowers powering a top-fuel dragster consume 900 crankshaft horsepower in an engine rated at 7,500 total horsepower). But superchargers can provide their boost almost instantly, whereas turbochargers typically suffer some response lag while the exhaust pressure required to spin the turbine builds. Clearly a top-fuel dragster trying to run the quarter in four seconds has no time to waste waiting for exhaust pressure to build, so they all use superchargers, while vehicles tasked with boosting a company's corporate average fuel economy can't afford to squander precious horsepower on blowers, so they mostly use turbos.
How Much Power Does A Turbo Or Supercharger Add?
Above we noted that the amount of oxygen that an engine can "breathe" is the limiting factor as to how much power it can produce, because fuel-injector technology is more than capable of supplying as much fuel as can possibly be burned with the amount of oxygen in the cylinder. Naturally aspirated engines operating at sea level get air at 14.7 psi, so if a turbo or supercharger adds 7 psi of boost to an engine, then the cylinders themselves are getting roughly 50 percent more air and should theoretically be able to produce about 50 percent more power. It doesn't usually work out that way. Compressing intake air adds heat, which along with the added pressure increases the likelihood of engine-damaging pre-detonation or "ping," so the timing often has to be retarded somewhat. This can limit the amount of time the fuel has to completely burn, and hence erodes some of the power gain. Most modern engines running turbos and/or superchargers also include intercoolers to help remove some of the heat added by the turbo or supercharger. In the end, the typical expectation is that adding 50 percent more air yields 30 to 40 percent more power.
How Do Turbos/Superchargers Save Gas?
When they're working, turbos and superchargers mostly help to burn more gas, but when they're bolted to an engine that would otherwise be too small to adequately meet the vehicle's needs in terms of acceleration or when towing, etc., they help save gas during the low-power cruising that comprises most of our driving. One of the ways this happens is by reducing the pumping losses that occur when a big-displacement engine is running at five percent throttle or less—it must work hard to suck air past a mostly closed throttle. That same amount of power might require a 20 percent throttle opening on the smaller engine, which results in less pumping work. (This is why many newer cars don't create enough vacuum to run power brakes, climate-control systems' blend-air doors, etc., and either feature auxiliary vacuum pumps or use electric controls for these items.)
So which is the better option? It’s kind of a toss up. We’ll leave that answer up to you and your wants.