BOOST BASICS | TURBOCHARGERS
story and photos by Dan Hankin

In the old days most builders left turbos to the diesel guys. When the import crowd started making big horsepower numbers with small displacement boosted four bangers in the 1990’s the domestic performance and muscle car crowd gave turbocharging a closer look. With modern EFI systems, computer controls, and advanced turbo technology builders can put together drivetrains that make monster power, yet deliver respectable fuel mileage and everyday driveability.

It's understandable to be intimidated by something you don't understand, but that's no reason to not dig in and learn something new! Lets break down the mystery of turbochargers in simple terms. While not every aspect of turbos can be explained simply, understanding the hows and whys of their operation can go a long way towards figuring out the rest.

There are five main parts of a turbocharger (see photo); the turbine housing and turbine wheel, the compressor housing and compressor wheel, and a connecting shaft. The turbo is mounted to the engine by bolting the turbine exhaust inlet to the exhaust manifold.

Exhaust exits the engine into the manifold, flows into the turbine, and spins the turbine wheel. The turbine wheel is connected via a shaft to the compressor wheel. The spinning compressor wheel then sucks ambient air into the compressor and forces it into the engine via a sealed tube, maximizing air intake. This is where we get the term "forced induction". We're forcing the engine to ingest more air than it could naturally. With more air in the cylinder, the engine is able to burn more fuel, making more power. An experienced tuner can alter fuel intake and timing to extract the most power and efficiency from a turbocharged engine.

Turbo Theory:
Many factors go into deciding the right turbo system for a vehicle. How much power you expect the engine to make, how much boost the engine can safely handle, where in the powerband you want the power to come on, and how big the engine is are all important questions to answer prior to selecting a turbo.A turbo that's too small for your application will spool fast, but will run out of boost early in the powerband. An engine with a turbo that is too large will suffer from 'turbo lag', taking a long time to spool and possibly never reaching boost.

The main goal in putting together a turbo system is to select a turbine that will spool as quickly as possible and a compressor that will generate its highest pressure as quickly as possible. In order for this to happen, the engine must produce enough exhaust to keep the turbine spooled in order to generate enough power to keep the compressor turning at its optimum level. Turbo lag happens when there is not enough exhaust to spool the turbine and power the compressor. When the compressor is not doing its job, the vehicle is running naturally aspirated - as it would if the turbo were not there.

Another well known fact of making horsepower is that a cooler intake air temperature will yield more power. A hot intake charge, particularly in a boosted vehicle, can also cause detonation. Because of this, many people install intercoolers in their turbo systems. An intercooler is a heat exchanger placed in the flow of air into the front of the car, and plumbed between the turbo and the throttle body or carburetor. Compressed air from the turbo compressor flows down into the intercooler and transfers heat from the intake air into the fins of the intercooler where it is then dissipated. The cooled intake charge is then sent to the throttle body or carb.A turbocharged vehicle should also run high octane gas to reduce the risk of detonation.

That’s it for turbo basics. Want to see more articles like this? Email me and let me know!