Lately, it seems that turbocharged engines have become all the rage as automakers chase increasingly stringent fuel economy standards. Turbochargers are known for boosting horsepower, so how do they improve fuel economy? They allow automakers to put smaller engines in cars without giving up the power that consumers have come to crave and to expect.
Even pickups and large SUVs often come with turbocharged engines these days.
What Is a Turbocharger?
A turbocharger, as its name implies, is a small turbine that sits under the hood and compresses the air that goes into the engine. Because it’s denser, more air molecules can be stuffed into the same amount of space inside each cylinder. (This denser air also requires more fuel, but we’ll get to that in a minute.)
The best part is that the turbocharger is turned with by the exhaust; as the exhaust comes out of the engine on its way to the tailpipe, it spins a turbine sitting in the exhaust manifold. That turbine is connected to a shaft that spins a compressor in the intake manifold.
The turbocharger doesn’t produce extra power – and thus require extra gas – until the driver demands it and presses down hard on the accelerator. Then, the engine takes in more air and fuel, and makes more exhaust. This spins the turbine and compresses the air. Fuel injectors add extra fuel to make a little turbocharged engine crank out big horsepower.
Where Did Turbochargers Originate?
For decades (starting with the Oldsmobile F-85 in the 1960s), turbochargers were used to give modest cars more power. Later, in cars like the iconic Porsche 911 Turbo, automakers strictly used them to make already-potent cars insanely fast. They used great big turbochargers that made a lot of extra power, but they took a long time to spool up after the driver hit the gas. That delay between when the driver pushes the pedal and the turbocharger kicks in is known as “turbo lag.”
The latest turbocharged engines are smaller – in many cases very small. The new Ford Focus and Fiesta ST use 1.0-liter three-cylinder engines. Since the turbocharger only produces extra power and uses extra gas when it needs it, these smaller engines get better gas mileage when the driver is just cruising along than a bigger engine would.
Their tiny turbochargers also spool up to speed quickly – more quickly than the whole engine could rev up to deliver similar power.
Do They Work?
Although today’s little turbochargers deliver significant gains in power, if the goal is to get better fuel economy, the results are mixed. Some small turbocharged cars deliver great gas mileage in EPA testing. Others deliver only incremental increases, and have trouble living up to those numbers in everyday driving. Automakers are chasing every tenth of a mile per gallon in EPA testing to boost their cars’ fuel economy ratings, so from their standpoint the turbos are a success. They wouldn’t spend the money on them if they weren’t.
Now turbos are making their way into the most popular vehicles in America: full-sized pickup trucks. The Ford F-150 offers two turbocharged V6 engines, a 2.7-liter and a 3.5-liter. The 3.5-liter develops the same power as the F-150’s big 5.0-liter V8, and it does so at much lower rpm. That makes it the perfect engine for hauling and towing. Some buyers may miss the rumble of the big V8 in the pickup, but the 3.5-liter V6 also gets two more mpg in EPA combined testing than the V8.
Turbos in Small Cars
The same results carry over to small car class. They make more power at lower rpm, so they feel much more relaxed to drive. That can be a revelation to anyone who hasn’t driven one of these models before. They have the feeling of bigger, more comfortable cars with more powerful engines, because they don’t have to downshift so often before delivering power for passing or climbing hills.
Older turbocharged engines developed a reputation as mechanical time bombs. Turbos spin at hundreds of thousands of rpm, and bearings often failed. Today, automakers have perfected the oiling systems that keep turbochargers going for hundreds of thousands of miles.
Older turbos made so much power that they frequently caused problems with other parts of the car. Transmissions would fail, brakes would need replacements more often, and engines would overheat.
These problems haven’t cropped up with smaller turbochargers on smaller engines. Automakers seem to have learned their lessons from older turbos.
Today’s turbocharged engines are much more reliable, and it’s rare to have major problems with a modern engine, whether it’s turbocharged or not.
Should You Trust a Turbo?
These days, small turbocharged engines deliver a better driving experience than non-turbocharged models. And while not all of them live up to their promised fuel economy, some do very well. Whether you’re looking for performance, high fuel-economy estimates, or reliability, it’s important to look at the ratings for each individual model you’re considering. A turbocharged engine, though, is no longer a good reason to eliminate a model from consideration.
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