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Turbo Technology - All Spooled Up
Turbos Explained And Secrets Revealed
When it comes to making a sick amount of horsepower, a turbocharger is a quiet and efficient way to get the job done. For many years, turbo technology lagged behind the other form of forced induction, but today there are more kits and improved tuning. It all combines to make a turbo setup just the ticket for your fast Ford.
Before we delve into the detailed portion of this episode, an understanding of the basics is needed. As most of you probably know, a turbocharger works in conjunction with exhaust gasses and the corresponding heat to drive a compressor that creates boost.
To understand how a turbo works, however, we need to take a look and see what exactly is contained inside. "A turbo is made up of five major parts," explains Nathan Page of HP Performance. "First, you have the compressor housing, which contains and directs compressed air into the throttle body [or carburetor]. Second, you have the compressor wheel, which draws in air and compresses it. Next, you have the centersection, also known as the bearing housing. This contains the bearings and seals that control oil for the turbine shaft. Obviously, you have the turbine wheel and shaft, which transfers the exhaust energy through the bearing housing to the compressor wheel. Finally, you have the exhaust, or turbine, housing, which collects and directs exhaust energy through the turbine wheel."
"The compressor wheel, which spins, draws in fresh air, and compresses that fresh air into boost, which is then pushed into the engine," says Squires Turbo Systems' Rick Squires. "This extra air increases the horsepower the engine can produce because it is taking in more air with the turbos' help than it could on its own."
By using the exhaust gasses of the engine, the turbo can efficiently provide forced induction, especially compared to a blower, which is driven by the crankshaft of the engine. "A typical internal-combustion engine wastes about 50 percent of its energy through exhaust gasses going out of the tailpipe," says Jim Napier of Turbo Horsepower. "Turbos recover some of that wasted heat and pressure, using it to push a large volume of air back into the engine."
Size 'Em Up
By far, the most crucial part of turbocharging any engine is choosing the right-size turbo or turbos. There are many different sizes from which to choose, and knowing which is best for you can be instrumental in keeping the power and fun meter up. "Turbo sizing is an art and a science," Napier says. "The science is very complex and can be driven by any number of tables that have been used over the years by professionals.
"Every turbo has a compressor map, which is a graphical representation of how that turbo performs. Turbo sizing is typically accomplished by experience and using any number of formulas that take into consideration engine displacement, camshaft, transmission, gears, type of intended use, weight of the vehicle, fuel injectors, exhaust system, lag time, and so on."
"The trick to properly sizing a turbo is like any performance project," Squires says. "The biggest problem we see is someone getting a 'deal' on a turbo and then starting the project based around the wrong turbo. You figure out exactly what you are trying to accomplish before starting to purchase components. We see too many people wanting turbos capable of high horsepower, when, in reality, they will never be making that much power. This is the case where you end up with turbo lag."
Turbo lag is the time it takes for the turbo to spool up and begin creating boost. "Lag occurs because of poor turbo sizing," Squires says. Simply put, less lag equals quicker boost production and better throttle response. Most professionals will trade a few peak horsepower for better midrange power, especially on a street-driven vehicle.
"Matching the compressor to the power level and boost requirements is where you start," Squires says. "Then, mating that compressor to the proper turbine wheel that will drive the compressor with the least amount of backpressure is next." It is also important to have an impeller designed to make boost in the proper rpm range.
An industry term thrown around among those dealing with turbos is the "A/R," or Area over Radius, ratio. "This [the A/R] is a relationship of the inner size of the conical shape in reference to the distance this inner duct is from the center of the shaft," Squires says. "Smaller A/R numbers will typically spool up the turbo quicker, while larger A/R numbers will offer more boost and horsepower up top."