The latest trend in hot rods seems to be forced induction, turbocharging specifically.. It is really old technology that has probably been around since the 1930's, but it is very simple and it works, so people continue to use it. The turbocharged trend seems to come and go in car manufacturers about every five or ten years from what I can tell. Here are just a few notable examples of factory turbocharged vehicles that you may or may not remember:
- The mid 1960's Chevy Corvair Flat 6 turbo
- The 1980ish Chevy Camaro 301 V8 turbo
- The Buick Grand National V6 turbo
- The 1989 Trans Am V8 turbo, very rare, very cool
- The Subaru WRX's flat 4 cylinder turbo
- The Mitsubishi Evolution 2.0L turbo
Now where were we...
The Turbocharger:
The turbocharger's job is to stuff your engine with as much air as possible without blowing it up. It does this with two wheels, known as a turbine and compressor. When I say turbine or compressor wheel, think "metal fan". It is pretty much what they are, just more fancy. The turbocharger is positioned in your exhaust stream so that exhaust gasses being pushed through your exhaust manifold spin the turbine wheel. This turbine wheel is on a shaft that has a compressor wheel on the opposite end. So when the turbine wheel is spinning, so is the compressor. The turbine side of the turbo is known as the hot side because of all the firey hell going past it. The compressor is known as the cold side because it blows "cold" air into the intake manifold. When I say "cold", it is by no means cold, it is well over a hundred degrees.... The faster the engine revs up, the faster the turbine wheel spins. The faster the turbine wheel spins, the faster the compressor wheel spins. The faster your compressor spins, the more air gets pumped into the intake manifold, and the faster you go. This process repeats itself until the wastegate opens.
The Wastegate:
A wastegate is pretty much a door in the exhaust that opens and closes when the engine tells it to. There are two different kinds of wastegates, an internal and an external. An internal gate is inside the turbo housing itself, where an external wastegate is a separate device mounted in the exhaust manifold before the turbo, or in the downpipe after the turbo. They both do the same thing, they allow exhaust gasses to bypass the turbo. Why the heck would you want that, you ask?...Well, you don't want your turbo pumping more air into the engine than the engine can handle. Although it sounds like fun, it isn't. So once the engine reaches a certain intake manifold pressure (boost pressure), the wastegate opens up and allows the exhaust gasses to go around the turbo to prevent the boost pressure from getting too high. Think about that for a moment. Ok, now you are wondering how the wastegate knows when to open, and I will tell you. It opens because of intake pressure. There is a vacuum line going to the wastegate actuator that controls the wastegate. This vacuum line comes from the intake manifold, so it has the same vacuum and pressure as the intake manifold. When pressure in the intake manifold builds up, the wastegate opens; when pressure in the intake goes away, and the wastegate closes. Simple enough right? But what if I want to set my boost at exactly 15psi? Well, that is where the boost controller comes into play.
The Boost Controller:
The boost controller controls the amount of boost pressures that the wastegate actuator receives from the intake manifold. It goes in between the intake manifold and the wastegate actuator, and is spliced into that vacuum line that we had talked about earlier. You set the boost controller to open at whatever boost pressure you want your car to have, let's say 15psi for example. The boost controller blocks off the pressure going to the wastegate actuator until it reaches the preset boost pressure. The moment it hits 15psi, a surge of pressure shoots through the boost controller to wastegate actuator and pops open the wastegate relieving the turbo of it's duties. This all happens in a split second, faster than a speeding bullet, maybe even faster than superman. Now you know all about the hot side of turbo, but let's not forget the cold side.
The Intercooler:
Air to air intercoolers are the kind that most people think of when the subject arrives. They cool the air coming out of the turbo before it reaches your intake manifold. They are like a high flowing radiator, but instead of antifreeze flowing through it, air does. As we learned in the last paragraph, the turbocharger has firey hell going through it the entire time your engine is running. This firey hell heats up the turbo and surrounding objects enough to turn the cast iron red at times. The closest thing to heat up is unfortunately the opposite side of the turbocharger, the "cold" compressor side. This is bad news because hot air does not make horsepower very well, and the compressor is the only place that a turbocharged engine is receiving air from. Luckily, the intercooler comes into play and cools the air. It goes between the compressor and the intake manifold and cools the air coming out of the turbo. They say that for every 10 degrees lower your intake temperature is, you gain 1% more horsepower (or something like that). That is why your car feels so much faster in the cold weather, it is!. So if you were to cool your intake temperature 50 degrees, which isn't THAT abnormal, you gain 5% more horsepower. If your engine was making 200 horsepower before, now your making 210. As you can see, having an intercooler is worth the effort and money. You can run a turbocharger setup without an intercooler, but it will not make nearly the power that an intercooled system would, and heats up the combustion chambers enough at times to cause detonation.
Another style of intercooler is the air to water intercooler. It is not as common as the air to air, probably because it is more challenging to install. It does the same thing as the air to air intercooler, cooling the air coming out of the turbocharger. However, instead of air flowing through the fins in the intercooler like a radiator does, water goes through it. That's right, the intercooler is in a sealed case submerged in a cool liquid. The liquid is pumped through the the system so it is constantly flowing, taking the heat away from the intercooler. Clever isn't it?
The Blow Off Valve: The blow off valve makes the "whoosh" sound that you hear everytime a turbocharged engine lets off the trottle. Although it is fun to listen to, it also serves the very important job of protecting your turbocharger. In simple terms, it is a big open / close valve located between your turbocharger and your throttle body. Let's say you have your engine revved up really high, the throttle plate is wide open and your turbocharging is working hard flowing massive amounts of air into your intake manifold. Suddenly you let of the gas and close the throttle plate. UH OH, where does all that air go that the turbocharger has already pumped through the intake piping? If there were not a blow off valve in the system, the air would get backed up in the system and put enormous pressure against the compressor side of the turbo . Not good. This is where the blow off valve (BOV) jumps in into the game. Intake pressure / vacuum controls the opening and closing of the blow off valve through a vacuum hose. When the intake manifold (after the trottle body) has vacuum in it (no boost), the valve knows that the throttle plate is closed, so the valve stays open. When the throttle plate is open, the turbo is pumping air, and the pressure goes up in the intake manifold, so the valve is closed. This means that every spec of air coming out of the turbo is going into your intake, nowhere else. The sound that you hear when the throttle plate closes is the sound of air whooshing out of the blow off valve to the atmosphere. Some vehicles recirculate this outgoing air back into the intake side of the turbo. That way it isn't wasted clean air. This is especially important to do in vehicles that use a Mass Airflow Sensor. The MAS, simply put, measures amounts of air going into the engine. If you dump already measured air out to the atmosphere, this will make your engine run poorly everytime you close your throttle, because it expects more air than it is actually getting. That is a whole separate subject that I will write about later.
So those are the basics of a turbocharger system. I am sure I will add on more, but for those of you that weren't sure what a turbocharger was or how a turbocharger works, that should help. Now it is time for me to go get something accomplished.
-HRCS