How Does a Turbo Work, and Why Are They in Ford Trucks?
EcoBoost technology has worked wonders for the F-150 and Raptor, but why exactly is that?
We may have a new administration in the oval office, but the fuel economy requirements for the entire fleet of Ford Vehicles will still be in effect for a while. Even so, it would make sense that the only vehicles left with V8s as primary engines would be Ford trucks. However, they play the biggest part in the big scheme of things, and with a V8 under the hood they could cause a huge drop in the global fleet economy number. So, what is the solution? Turbochargers and less cylinders.
If you’re unfamiliar, a turbocharger is a form of forced induction (fi) that increases the amount of air being forced into engine during the intake cycle. At least that’s the simple way of looking at it. The reality is that turbocharging is very complicated, and we’ll touch on the finer details like compressor maps, A/R, and more later.
How Does a Turbocharger Work?
We’re sticking to some of the basic details so you’ll understand what’s going on inside the magical snail. A turbocharger is made up of a compressor and a turbine. The turbine is on the exhaust side and it drives the compressor wheel which forces air into the intake. The compressor wheel is where the forced air comes from, and it’s called a compressor. The compressor wheel increases the volume of air to above atmospheric pressure, and that’s called “boost”.
Atmospheric pressure is the pressure you feel around you at the moment, and it is 14.7 psi at sea level. As you increase or decrease your altitude, you increase and decrease your relative atmospheric pressure. That is the reason why a boost gauge never reads in absolute pressure and just reads boost pressure. A turbo may increase the engine’s atmospheric pressure by 7 psi, for example, but 7 psi for some may be 21 psi for others depending on their altitude.
The turbine and compressor wheels are connected by a shaft that spins on a bearing, which will either be a bushing bearing or a ball bearing. Bushing bearings are usually made of a softer metal and rely on oil to keep the shaft spinning freely, while a ball bearing will use — ball bearings. The ball bearing style is typically more efficient, but also more expensive. With that in mind, you may wonder why Ford doesn’t use superchargers instead?
Why Not a Supercharger?
While they both use boost to help the engine produce more power, there is a difference between a supercharger and a turbocharger. The most obvious difference is that a supercharger is a belt driven forced induction system, which uses the engine’s crankshaft to drive its compressor lobes or the gearbox attached to the compressor. Inside the snout of the supercharger is a pair of gears which transfers the spin of one lobe to the other. It’s also where the supercharger gets its famous whine noise.
While the advantage of a supercharger is near instant boost, the advantage of the turbo is efficiency. Instead of using a belt on the crank of the engine to turn a gear, the turbo uses wasted gases from the engine to create boost, which makes more horsepower and torque. Also, unlike superchargers, manufacturers can control the amount of boost the turbo creates by using a form of boost control.
However, much of the flack the turbocharger gets is that “they are dirty,” and from an emissions control standpoint, you would think having a big heat sink wouldn’t work well with the catalytic converter and its pre-converter. Well, the modern turbocharger can take more heat than its predecessors from a decade ago. That means it doesn’t work like a heat sink as much as it used to, and the heat from the exhaust can now travel down into the converter.
“The OEM Turbos we produce are rated to 760-degrees to 950-degrees Celsius (1400-degrees to 1742-degrees Fahrenheit) at the compressor inlet,” says Harut Stepanyan, Application Engineer at Honeywell Garrett, “then at the outlet we’re still seeing about 700-degrees Celsius (1292-degrees Fahrenheit), so there is still plenty of heat reaching the catalytic converter.”
So, how does this all really work? How do you get the same power out of a V6 plus fuel savings, over what you get with a V8 engine? “You’re feeding less cylinders,” says Stepanyan, “The biggest change from turbos in the ’80s and ’90s has been the aerodynamics. The compressor wheel blade shape, the turbine wheel blade shape – thanks to CFD we can optimize the blade shape and curve to increase the efficacy of the turbo to produce more power at the wheels.”
In doing so, you reduce the need to produce more exhaust gas flow to the turbine, and get more boost pressure from the compressor. A Garrett T25 could produce about 300 horsepower but now the GT2871R can now produce at or around 400 horsepower on a 3.0-liter V6. Then there are the improvements in automatic transmissions! By keeping the engine in its most efficient powerband, you get better fuel economy with better power and torque.
So, by feeding less cylinders Ford achieves the fuel mileage necessary to keep the government happy, but consumers still get the power and torque they expect thanks turbochargers. These improvements are only going to continue as we’re starting to see gasoline engines get variable vane technology similar to diesel engines. In addition, decreasing costs of materials and research will enable technology to spread even further.