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KFYO Automotive: Understanding Turbochargers

Volkswagen, VW.com

More and more modern car manufacturers are producing affordable turbocharged vehicles. Turbochargers can be found in Volkswagen’s Passat (pictured, above) and GTI, KIA’s new Optima, and even Ford’s Mustang and F-150, to name just a few.  But what exactly are these devices, and what are they really doing for your engine?

Turbochargers are a form of “forced induction.” This means it pushes more gas-air mixture into an engine than would normally occur in a naturally aspirated engine, or any non-turbo/non-supercharged engine.

Here’s a video, which also explains the differences:

The turbocharger is not a new invention. In fact, the concept of forced induction has been around for over one hundred years. They have not always been popular for a number of reasons, however.

In my opinion, there are three primary strikes against the turbocharger. Firstly, they are fairly complex, incorporating moving parts and high pressures. It is completely possible for a turbocharger to fail or break. Secondly, these components are expensive, and until recent times were not found in what would be considered “affordable” cars. And thirdly, a turbocharged engine will, to one degree or another, suffer from something known as “turbo lag,” but we will get into that in a second.

So, if there are these strikes against turbos, why do people want them? Well, most critically, they increase the performance and efficiency of an engine. By increasing the power of an engine, smaller displacements can be utilized while still achieving adequate performance. The result is better fuel efficiency. But the real question is, how does a turbocharger achieve this increased power output?

In layman’s terms, a turbocharger is essentially a compact and contained fan that is “spooled,” or spun, by the exhaust gasses of a combustion engine. When the turbo spools, it pressurizes the gasoline-air mixture going into the engine, producing more power.

This is why a 2014 VW 1.8T (turbo) engine can match the horsepower (and exceed the torque) output of the larger 2014 VW 2.5 L naturally aspirated engine, despite being down one cylinder and more than half a liter in displacement.

One of the inherent problems with turbocharged engines is that they require a certain amount of exhaust gasses to spool.  This is known as the “boost threshold.” Until this threshold is met, the turbo is practically inactive, meaning the engine will put out reduced power, as a naturally aspirated engine would. As the driver stomps on the gas pedal, RPMs increase, the gas builds, the turbo spools, and the engine’s power increases. The time between the gas pedal being pressed and the turbo actually spooling is the turbo lag.

While not necessarily a problem for anyone but a race car driver, turbo lag does take some getting used to. When I bought my small, 2.0T Volkswagen GTI after driving a 5.4 L F-150, I remember stepping on the gas, temporarily wondering why I wasn’t moving, and suddenly being boosted away as the turbo spooled up.

This can actually act in the drivers favor. If feeling especially frugal, the driver can keep the engines RPMs below the boost threshold and reap the benefits in a gas mileage increase. This practice is known as “staying out of the boost.”

In recent years, the prices for turbo setups have constantly decreased, while reliability has improved. Boost thresholds have also been lowered, meaning less turbo lag. This is a winning formula, as all three of the primary problems found with turbochargers are minimized.

The end result is a modern car with excellent fuel economy, good reliability, and a decent price. A good example is the Chevrolet Sonic Turbo with it’s 33 mpg combined, or the sportier Ford Focus ST with a 0-60 time under 6 seconds. It is no wonder modern car manufacturers are turning out more and more turbocharged vehicles. In my opinion, now is a great time to jump on the band wagon and at least test drive a couple of turboed cars next time you go car shopping.

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