Forced Air and the Future

Nothing like a little mouth to mouth to get you breathing deep

Forced induction. These two words together can make a grown man salivate in a way that not many other things can. What this term refers to, in relation to the function of the automobile, is any device or method that forces more air into the intake of an engine. Forcing more air into the engine means that more fuel can be burned when needed, and more power can be produced by the engine when needed.

Many people think that the force that causes the air to flow into the engine is the suction created by the piston moving down in the cylinder with the intake valve open. This is not true. The piston moving down only creates a vacuum, which is an area of negative pressure. Once this void is created something will rush in to fill it, and that something is air. The motivation for the air is atmospheric pressure. This is one of the reasons that the average car or truck will produce more power at low elevation versus high elevation.

At sea level normal air pressure is 14.7 psi. This means that a column of air at sea level measuring one square inch, reaching all the way up through the atmosphere, weighs 14.7 pounds. The further up from sea level that you measure the weight of the column, the less it will weigh. In Denver, CO the column of air will weigh about 12.2 pounds. In Leadville, CO which is a town over 10,000 ft. high in the Rockies, the column will weigh 10.3 pounds. Because of this decrease in pressure, a car that is operating at this elevation will not be as powerful. The other thing that goes along with this is the fact that at higher elevation the oxygen content of the air is lower.

In the early days of modern aviation the service ceiling of the average aircraft was limited by this same fact. If an airplane flew too high it would loose power. Forced induction systems first showed up on aircraft during WWI. This allowed the planes to fly much higher than they otherwise could have. Like so many other bits of technology that improved aircraft, it was only a matter of time before some mechanic said, “I think I should try bolting one of these things on my car.”

Types

Forced induction systems can be divided into two distinct groups, turbochargers and superchargers. In reality a turbocharger is a type of supercharger but usually the two do not get lumped together into the same category because they don’t operate the same way, even though they essentially accomplish the same task.



A supercharger

The supercharger is a belt driven compressor that forces large amounts of air into the intake manifold. A belt similar to the type that turns accessories such as the alternator or the A/C compressor will be used to turn a set of screws within a housing, that are in mesh with each other, or some kind of similar device. The amount of pressure that a supercharger will build varies from one engine to another but it is usually somewhere between 8 and 15 psi. Since the supercharger is turning anytime the engine is running it can build boost very quikly.



A basic turbocharger setup.



The turbo charger compresses air and forces that compressed air into the intake manifold but it is driven by exhaust gasses exiting the engine through the exhaust ports. These gasses spin a wheel that is attached to a shaft. On the other end of the shaft is another wheel that compresses the incoming air. Turbochargers will produce boost pressure in the same neighborhood as superchargers do but they do not drag on the engine because they are not driven by the crankshaft. This sounds like a great advantage for the turbo but there is also a problem. This problem is reefed to as turbo lag. This is used to describe the brief period of time between initial throttle application and the point at which the turbo is spinning fast enough to create boost. Superchargers do not suffer from this kind of lag.

The Future

In the past, any vehicle with a forced induction system was considered high performance, or at least higher performance then the equivalent vehicle in a naturally aspirated form. A forced induction system fitted to an engine that could already be considered high performance makes for a real screamer. Top Fuel dragsters have massive superchargers breathing air into massive engines. These cars can run a quarter of a mile in about 4 seconds. A tremendous amount of air is forced into the engine in order to burn a tremendous amount of fuel. In the real world we only need lots of power for brief moments here and there. Like when we are getting on the freeway, passing a slower vehicle on a two lane road, or when we are trying to beat another car to a prime parking spot at the mall. The rest of the time we only need a small amount of power to get around.

With all of the talk about new automotive technologies that are very advanced and becoming more widely available, the one that does not get as much attention is the new turbocharged engines, and the high levels of efficiency that they obtain. They probably don’t get a lot of attention because the technology is really not that new. This instance just sees the technology applied in a slightly different way. With the proper application of a turbocharger, an engine’s output and efficiency can be raised enough to make the engine seem like something much bigger than it really is. 4 cylinder engines can easily have the power of a V6 and a V6 can have the power of a V8. This can happen without sacrificing fuel economy because small displacement engines are used, with variable geometry turbos, and the only time the engine needs to put out big power is under heavy load. The rest of the time that the engine is running, the smaller size helps it get better fuel economy.

2011 Chevrolet Cruze

The Ford Ecoboost engine is a great example of an engine that puts out tremendous power when needed but still gets great fuel economy. The V6 Ecoboost engine that is available in a few different models puts out somewhere between 300 and 360 HP and gets about 20 to 25 mpg. The Chevrolet Cruze also uses similar technology. The 1.4 liter turbocharged engine in the Cruze, gets about 40 mpg and delivers 138 HP. This is pretty close to what some hybrids of the same size achieve but at literally half the price.

2011 Ford Taurus

Why isn’t everyone using these kind of forced induction systems on all of the vehicles they build? The biggest reason is cost. While a small turbo setup might be much cheaper then a hybrid drivetrain, it still costs more than an engine that doesn’t have a turbo. If gas prices keep going up, which they will, all of the manufacturers will have to adapt some way or another, because the public will demand more efficient vehicles that get better gas mileage. Maybe smaller engines with forced induction systems will be the best answer for all of them.

With the current spike in gas prices sales of SUVs and big trucks are down, and the sales of smaller more fuel efficient vehicles are up. The Ecoboost F150 is selling much better than Ford expected. This is a big truck that usually appeals to people who would never buy anything with fewer than 8 cylinders. When the cost to fill your tank goes through the roof, you change the way you think, and then suddenly a V6 powered pickup truck doesn’t seem so bad. Not only does it not seem bad, in all reality it isn’t.