Turbochargers and the Intake Charge

Adding a turbocharger to your car will give you one of the biggest increases in horsepower over any other engine modification. Nitrous oxide systems can rival the power performance, but not the durability and constant gains associated with a turbo system. Turbochargers can be tuned to give you any amount of boost between 0 and 24+psi of boost, depending on the size of the turbine. When you have any type of forced induction system like a turbocharger, you want to make sure that the engine is tuned to it. Below we will discuss the importance of the air fuel ratio. I will revisit this again, because premature detonation is a major cause of internal engine damage, and detonation can be caused by a very lean air fuel ratio. Turbo kits should be coupled with an ecu that is tuned to deliver more fuel than the factory settings, and the fuel delivered to the engine should be increased proportionally to the boost pressure. You also should add an air charge intercooler, which will reduce the intake charge air temperature. The air coming from the exhaust has been heated tremendously, and should be given the opportunity to cool before being re-entered into the system.
Beware of bolt on turbo kits. They in themselves are not the all in all for horsepower. You will have to match these with an intercooler and ecu to build a system that will have durability and performance. These bolt on kits are great for the experienced installers who can tune an engine correctly. The true power behind a turbo kit will be unleased with some tuning to the heads, the timing and fuel ratios, and the intake manifold. We will be discussing each of these in future post, beginning with the heads. The heads are where the power is made because they are a direct path to the combustion chamber, which is where the magic happens.
Internal combustion engines are "breathing" engines. That is to say, they draw in air and fuel for energy. This energy is realized as power when the air-fuel mixture is ignited in the combustion chamber. Afterward, the waste created by the combustion is expelled. All of this is typically accomplished in four strokes of the pistons. What a turbocharger does is to make the air-fuel mixture more combustible by fitting more air into the engine's chambers which, in turn, creates more power and torque when the piston is forced downward by the resulting explosion. It accomplishes this task by condensing, or compressing, the air molecules so that the air the engine draws in is denser. Now, how it does that is the real story here.
A turbocharger is a way to force air into the engine. Hot exhaust gas powers the turbine wheel of the supercharger to make it rotate. That turbine wheel is connected by a shaft to a compressor wheel. As the turbine wheel spins faster and faster, it causes the compressor wheel to also spin quickly. The rotation of the compressor wheel pulls in ambient air and compresses it before pumping it into the engine's chambers. As you may have guessed, the compressed air leaving the compressor wheel housing is very hot as a result of both compression and friction. That's where a charge-air cooler (or "intercooler") comes in. It reduces the temperature of the compressed air so that it is denser when it enters the chamber. The intercooler also helps to keep the temperature down in the combustion chamber. All together, the engine, turbocharger and charge-air cooler form what is known as a "charge-air system". Some systems also include a tip turbine fan which draws air across the charge-air cooler to further reduce the temperature of the compressed air generated by the turbocharger.
The basic principal behind turbocharging is fairly simple, but a turbocharger very complex. Not only must the components within the turbocharger itself be precisely coordinated, but the turbocharger and the engine itself must also be exactly matched. If they're not, engine inefficiency and even damage can be the results. That's why it's important to follow correct installation, operating and preventative maintenance procedures.
When adding a turbocharger or other forced induction system to an engine, you need to pay close attention to the air/fuel mixture ratio, as running lean can cause damaging detonation. Also pay attention to how much air the heads can efficiently flow. This is more difficult to measure or calculate, but much like the diameter of a straw can effect how much liquid it can draw, the heads will limit how much air they can flow through the system.