Which is best and why?
Supercharging vs turbocharging - which is best and why? Well, as man has always strived to improve himself and the world around him through technology, he has experimented with endless means of enhancing the performance of machinery, including engines. This has led to the creation of engines that eschew atmospheric pressure in favor of forced induction. The two main types are supercharging and turbocharging, with twincharging a mixture of both. Regardless of how it is achieved, forced induction can dramatically improve performance and efficiency while increasing weight and complexity by a relatively insignificant amount. The benefits are thus meant to outweigh the drawbacks, but there is a reason that one kind of forced induction is more popular than any other. In this article, we'll briefly explain each kind of forced induction to explain the difference between a turbocharger and a supercharger, and answer some of the frequently asked questions on the subject of these different sorts of 'air pumps', so to speak.
If you want to get a comprehensive understanding of how turbocharging works, read our in-depth article on the subject here. In the meantime, we'll give you a basic overview of what it entails. In a turbocharged motor, exhaust gases that would otherwise be wasted are used to spool up the exhaust wheel in the exhaust housing of the turbocharger. This wheel is connected to another just like it in the compressor housing of the turbo. This connection allows the compressor side to spin at the same rate as the exhaust side, and this creates boost pressure. This boost pressure circulates through the turbo system and into the intake, increasing air density. With greater density of the air/fuel mixture, more power can be extracted, the explosion in the combustion chamber is greater, and the exhaust gasses exit into the turbo, starting the (continuous) process over again. Due to the fact that the boost needs to build, turbocharged engines can be slow to produce power.
Superchargers work much like turbochargers, creating boost for a denser air/fuel mixture, although there are numerous different types as discussed here. However, while turbochargers use waste products to spool up, superchargers typically sap power before they produce any. In most cases, the supercharger system is a positive displacement type connected to the crankshaft of the engine by a pulley with a belt. This belt rotates with the crankshaft, building boost pressure in the same sort of chamber as the compressor housing of a turbo. As the speed of the engine increases, so the boost pressure produced by the supercharger increases, with this making its way into the intake of the engine in much the same way as a turbo. This linear way of increasing power means that throttle response is excellent, but for small capacity engines, it is generally not economical or viable as each cylinder is essentially being overworked before it even produces power. So while turbochargers (or turbosuperchargers, as they are correctly defined) are much more efficient and less complex, they cannot compete with the throttle response provided by a supercharger. While supercharging is often found on muscle cars like the Dodge Challenger Hellcat, and on sports cars such as the Lotus Evora, it is also used in the V8-powered Land Rover Range Rover Sport.
So we've determined that turbochargers are more efficient than superchargers, but the latter provides better throttle response. So surely the best way to force air into an engine would be with both turbocharging and supercharging? In theory, this would be ideal as you'd get good throttle response and good efficiency. Well, this has been attempted and proven as a viable option, but there are a number of drawbacks too.
First, let's see how such a system works.
All in all, a series system sounds like the perfect setup, especially when the supercharger can be bypassed or mechanically decoupled from the drivetrain via an electromagnetic clutch and bypass valve. In this scenario, efficiency is at its peak as the turbo is up to speed and the supercharger is no longer drawing from the engine.
As you can probably tell, the drawbacks are obvious: complexity and weight increase considerably, and you need numerous additional components to feed both the turbocharger and the supercharger with air, oil, and water. Thus, you need a bigger, more capable water pump, a large intercooler, and of course, loads of boost piping. The most important aspect, however, is the tuning, which must be absolutely spot-on to have any hope of being reliable or even smooth to operate. This is why aftermarket twincharged engines are very rare, and OEM twincharged cars have very little room for tuning potential. Some supercars like the Zenvo ST1 are twincharged.
Now that you understand how each system works, below are some examples of cars that use each. Twincharged engines are the rarest these days, followed by supercharged engines. Turbocharged cars, on the other hand, proliferate the market.
Volkswagen Polo GTI (6R generation, 1.4-liter motor)
So which wins? Well, we've determined that twincharging is out of the running due to weight and complexity. Potential is also very limited, but the limiting factors here come mainly from the supercharger. While standalone superchargers can produce more power, they are less efficient. Twincharged systems are more efficient but more limited. With turbochargers, cost, weight, and complexity are, in general, all at their lowest. Of course, turbos have their pros and cons too, with the latter including turbo lag. However, the difference is that the benefits of turbochargers are too great to ignore: they're relatively affordable, they're relatively simple, and they are commonly available. That being said, some applications perform better than others, so supercharging and twincharging are not dead. For large-capacity engines, superchargers tend to be easier to work with, while small-capacity engines can outperform themselves with a twincharged setup. For everything in between - the bulk of powertrains out there - turbos provide a great balance of response, performance, and efficiency.
It depends on the configuration, but as a rule of thumb, turbocharging is favored for cost, weight, complexity, and efficiency.
Yes, but diesels typically provide good low-down torque, so supercharging is not usually necessary or viable.
Yes, typically. Usually, spotting the boost pipes for either system is easy, and in many cases, the turbo or supercharger itself is visible in the engine bay. However, some motors may hide the turbo behind the engine, especially in a transverse layout such as a Golf GTI. This makes sense as the exhaust piping can be shorter and the intake can be closer to cold air.
Typically, no. The technology is much more common in aviation than in the automobile industry, so superchargers aren't developed by as many companies nor used by automakers very often. As a result, supercharging your engine will typically be more expensive than turbocharging one.