Turbo Basics

In plain and simple English.

Don’t you hate tech articles that confuse you more than help you understand the true concepts of things. Tell me if this sounds familiar. You see a tech article in a magazine and are interested in learning about the topic, but after reading it half way through you become frustrated and move on to something else. It’s like the tech article was too technical. All the high tech mumbo jumbo (which is often inaccurate) did not help much either. Well here is my crack at turbo basics, in plain and simple English for the everyday racer who is far from being an engineering graduate and being a turbo techno guru.

Why do people turbocharge their cars? Why do people drive well over 100 mph when a signs says that the limit is 65? It is simply for the thrill and the rush. For the love and need of SPEED and POWER. Power that is always there at the tip of your toes twenty four hours a day seven days a week. Turbocharging your car can net a 50% increase in horsepower if not more. I’ve seen Honda Civic coupes (which have 125hp stock) double it’s horsepower output by turbocharging. But be warned any plan to increase horsepower over 50% of the stock power will definitely need some bottom end build up and engine management controls. If you are planning to turbocharge your car, here is some advice. Take your time, "do your homework", ask a lot of questions(to the right qualified people), and do it the right way the first time around. Believe me, their is nothing like the power of a turbo and the fun factor drivability is beyond awesome.

How does it work? Well here is a general bare bones run down of how a turbocharger system works. The engine produces exhaust gases that exit via the exhaust ports of the cylinder head. These exhaust gases flow through turbo manifold ( just like it would through a DC header) into a turbocharger unit. As the exhaust gases enters the turbine housing the velocity of the exhaust gas "spools" (spins) a propeller bladed type wheel called the "turbine wheel". As this turbine wheel begins to spin, it turns and drives a common shaft. This shaft has another propeller type wheel called the "compressor wheel" on the other end. The compressor stage of the turbo begins to suck air in as the "compressor wheel" begins to spool. The "compressor wheel" spools faster and faster and the air becomes "compressed charged air"(it’s like a hair dryer in your engine bay). The faster the wheels spin, the faster the shaft speed, and thus the greater the pressure. From the compressor stage of the turbine the "charged air" exits at a great velocity and makes its way to the intercooler. The intercooler is a huge heat exchanger (which is like a radiator but for air). It cools down the temperature of the "charged air". From the intercooler the air travels to the throttle body and back into the motor. As more air is force fed into the motor, an additional amount of fuel must also be added. The amount of fuel must be proportionate with the amount of air that is supplied to the motor. Bottom line - more air and more fuel equals more power.

Turbo boost! A turbocharged engine revolves around one central idea and that is boost. Boost is defined as the increase in manifold pressure above atmospheric pressure. Boost is a gauge measurement of turbocharger compressor discharged pressure. So what the hell does that mean? Basically boost is the value (amount) of "charge pressurized air" coming out of the turbocharger. In general the higher the boost, the more air will be force fed to the motor, and more horsepower will be made. Boost is usually measure in PSI (pounds per square inch) or bar (inches in mercury level).

The basic components

Turbocharger - The turbocharger is an exhaust driven compressor. It has 3 main housings.
1- The turbine stage (which drives the compressor stage) is the side connected to the exhaust manifold.
2- A center section (CHRA) which houses the common "shaft". The center section is also were oil and water flow to keep the temperature of the turbocharger down.
3- Then there is the compressor stage from which the "charged air" is created and discharged.

The turbo has two propeller type wheels connected by the common "shaft". The "turbine wheel" and the "compressor wheel" which both spool up to create the "charged air".

Exhaust manifold - The exhaust manifold holds the turbocharger and mounts it to the motor. The exhaust manifold directs the exhaust gases from the exhaust ports to the turbocharger inlet. It is typically made in cast iron, mild steel, or stainless steel.

Down pipe - the down pipe is connected to the side of the turbine stage of the turbocharger and it directs all exhaust gases from the housing into the exhaust system. When turbocharging a car, it is often a rule of thumb to run the least restrictive type of exhaust available to keep back pressure to a minimum.

Intercooler - the intercooler is a giant heat exchanger that cools down the temperature of the "charged air". Usually when "charged air" is created it is very very hot, so it must be cooled down. The colder the air (making the air more dense) is when it enters the motor, the easier it will combust and at most times the more power it will make. Not all turbo systems use intercoolers but it is always better to have one.

Blow-off valve - a blow off valve is a spring loaded valve usually placed on the pipe between the intercooler and throttle body and it is used to prevent "compressor surge". Basically it helps the turbocharger unit last longer and increase responsiveness. Blow-off valves give off a distinct yet impressive hissing sound. It’s the sound that screams "I’m turbo and if your not, than you better think twice before you try to run me!!!"

High flow fuel pump - At many times the stock fuel pump cannot supply ample fuel that a turbocharged engine needs. For this reason a high flow fuel pump must be added. What this does is raise the fuel pressure so when the additional fuel is needed the capacity for it is there.

Boost dependent fuel regulator - As we stated before as the more air goes into the motor the more fuel is needed. A boost dependent fuel regulator regulates the amount of fuel that goes to the injectors. As the turbo begins to spool, boost pressure builds up and as the boost pressure increases the boost dependent fuel regulator pushes more fuel to the injectors which is sprayed into the motor.

Wastegate - The wastegate primarily controls boost pressure. It is an exhaust by pass valve that opens and closes to let out or keep exhaust gases. It maintains the turbocharger’s shaft speed by this open and close action. When it opens exhaust gases leave via the downpipe and then through the exhaust system thus the shaft speed is slowed down. When it stays shut the exhaust gases increase shaft speed by spooling the turbine wheel.

As stated before any increase of horsepower output over 50% will most probably require bottom end build up and fuel and engine management controls. If you plan to turbocharge your vehicle, be sure to get all the necessary parts or you’ll be towing your ride home real quick. Air filters are important. They help keep dirt and other things out of a turbo, so be sure to have one. Also maintain a clean oil supply. This means that you will have to change oil more often but it will help for durability sake.

Well that about sums it up. I hope that I have helped you understand some of the basics of turbochargers. The only thing left to do is for you is to go out and experience the thrill. It’s like jumping in your very own roller coaster ride. The fun factor drivability exceeds a 10+ (on a 1-10 rating scale). Don’t take my word for it. Get out there and experience BOOST. Your life may never be the same.