You know, this site isn’t named kuhol.net for nothing. We like turbocharged cars. We have a fascination for the exhaust-driven supercharger, the sounds it makes, the whoosh of an open compressor bypass valve, the power it creates.
We’ve always wanted to have our car turbocharged, and we were able to, some time back. We’ve extensively read about the subject, and after the conversion, we have gone through a whole bunch of issues with the car. And got them resolved, and resolving many others up until today. We think ourselves more than knowledgeable about turbocharger setups. Don’t expect us to weld you up an exhaust manifold or wire up a tuning device, though.
We’ll be commencing this series of articles about turbos and turbocharging. By writing these, our intention is to steer the people who have absolutely no idea what a turbo is and what a turbo setup and conversion entails. We hope that you will be able to learn a thing or two about them.
The topic starts on the basics of turbocharging. The next article will describe what a turbocharger is. If you do find that we have written something incorrect, please do not hesitate to comment away.
What is Turbocharging
A turbo is part of the family of related apparatuses called superchargers. We will define a supercharger as a device, usually mechanical in nature, that provides an excess of air to the powerplant, beyond what the engine can suck in by itself. As you will see later, that “device” may not be explicitly “mechanical”, as long as it brings in more air.
To see the importance of supercharging in general, we’ll use an example. An engine, say, a single-cylinder engine. Rated with a displacement of xxx cc, the engine is expected to suck in approximately less than xxx cc of air and fuel while aspirating normally. This action is due to the vacuum generated by the piston moving downwards in the induction stroke of the Otto four-stroke cycle.
Why the engine cannot usually suck in its rated displacement of air is because there are limits to how well it gulps in air. The amount of air molecules that would be present for combustion will be limited by the ambient atmospheric pressure, temperature, and the basic engine’s ability to suck in air vis-a-vis its displacement, the latter being a term called volumetric efficiency.
There are four ways to increase the engine’s horsepower output, all things constant, or what we economists call ceteris paribus. One is to increase the engine’s efficiency to breathe in more of that fuel-air mxture, and also to control how it propagates in the combustion chamber. Another is to increase the size of the single-piston engine by increasing the cylinder bore or piston stroke. Or, add more cylinders to the engine. Or increase the speed that which the engine spins.
There is actually a fifth way, which is optimizing the rate of combustion via proper timing of ignition and ensuring near-stoichiometric mixtures of fuel and air. That is the realm of engine management, which we have detailed in a series evaluating engine management solutions.
The supercharger is relevant to the first method of making power, making the car breathe more. Sans supercharger, the engine’s volumetric efficiency can be improved by making sure the car can respirate properly while “inhaling” (more intake valves, optimizing intake runner design, valve overlap, adjusting valve lift and duration via lumpier camshafts, adjusting valve timing via cam degreeing, freer-flowing air cleaner,) or while “exhaling” (more exhaust valves, free-flowing exhaust system, tuned-length exhaust manifold, rest of the camshaft-related stuff).
With the above done, a determined-enough tuner can even exceed 100% volumetric efficiency. Just turn up the revs and you will get more than decent power from the motor.
But, turning up the revs is not as easy as one might think. The tensile force acting upon the engine’s reciprocating parts (primarily the connecting rod) is tremendous. Tensile force can be imagined as the stresses pulling something apart, as opposed to compressive forces, which squeezes something. When the con rod stretches beyond breaking point due to high enough revs, it usually takes out a whole bunch of engine parts.
Thus, the option of supercharging. Have a device called a supercharger to force in more air into the engine. Squirt in more fuel. Combust the more dense fuel-air mixture. Then, you have made more power.
The more fuel-air mixture you combust, the more power you make. Supercharging is thus equivalent to increasing the engine’s size to accommodate more of that mixture to burn.
There are various types of supercharging technologies available, which we will discuss next time. The one we are focusing on is the turbosupercharger, also known as the turbo. A turbo is a supercharger that is driven by the engine’s exhaust. This design has a few advantages over mechanically driven superchargers, which we will thresh out in the next article.
What does one expect with fitting a custom turbo setup on one’s car? With a stock engine in reasonably good health, a moderate “boost up” can be tolerated by it without mechanical modification, with engine power able to match or exceed the effort if the same powerplant were supertuned yet remaining naturally aspirated. With engine fortification and a lot other supporting modifications, the engine can produce a superfluous amount of power, beyond 150 or 200HP per liter of displacement.
Turbos are prevalent in motorsports. Formula 1 has re-embraced turbochargers starting this season. Many Le Mans endurance racers, most notably the Audi TDi cars, are turbocharged as well. You’ll see these conical things huffing out racing vehicles both locally and internationally, in almost all motorsport categories, making racers competitive and victorious.
For our car manufacturers, they use turbochargers as original equipment nowadays to make decent power from small sized engines. Given the trends towards eco-friendliness and rising expectations on a car’s fuel economy, turbocharging downsized engines is increasingly being used to meet these goals while being able to meet consumer expectations on power output. The concept of Ford with their Ecoboost family of engines is one example of this.
Turbochargers mounted on diesel engines fitted with modern common-rail direct injection systems are becoming ubiquitous on light trucks, multipurpose vehicles, and even cars. These engines are appreciated for both their tremendous power and torque figures and thriftiness on the pump.
Now, do you need a turbo in your life? Not so fast, young Padawan. Please do wait for our future installments of this series of articles for more about turbos and turbocharging. Feel free to let us know about what you think so far, we would very much appreciate it.