Do You Know How Hood Scoops Work?
Hood scoops are curious things. They seem to come and go in automotive design as if some sort of fashion accessory, falling out of favor during one decade and in favor the next. In truth, hood scoops are not necessary technology for automobiles to have but they can enhance a car’s performance if designed properly. Many performance cars use hood scoops for just that reason.
The way that hood scoops work is actually pretty simple, but not widely known. First consider how internal combustion engines work. Unless the engine carries its own oxygen supply (like a rocket engine), it gets that oxygen by burning the surrounding air.
Cool air is denser than hot air and thus has more oxygen in it, which produces more power when it burns. Since modern automobile engines have normal operating temperatures well above 160°F and the space under the hood is usually cramped, the air in the engine compartment is usually considerably hotter than the outside air. If the engine takes its intake air from under the hood, its power output will be reduced, sometimes by as much as 10%. The obvious solution is allow the engine to breathe cooler, denser outside air, such as from a hood scoop.
You may have noticed that there have been various hood scoop designs over the years. Some have been modest and others quite pronounced and each type has a particular design philosophy behind it.
Here are a few you will see being used:
Raised Scoops – These are the ones that stick up in the air. But why so high, is that for show? Not really. Any moving object is surrounded by a thin layer of slower-moving air known as the boundary layer. This layer is right on top of the outside surface of an automobile. To avoid this boundary layer, raised scoops stick up noticeably from the hood. This allows them to not only funnel cool air down into the engine but enjoy a ram-effect whereby air is pushed into the engine.
Cowl-induction Scoops – Many scoops face forward in the direction of the oncoming air, but every so often you’ll see a reversed scoop, facing away from the air stream. Why is that? The way this works is that the area at the base of the windshield on most cars is actually a high-pressure zone. If a reversed scoop is mounted close enough to the windshield, that high pressure will force nice cool air right into the scoop.
Shaker Scoops – If you are a muscle car enthusiast then you know what shaker scoops are. They are scoop assemblies mounted directly to the engine and the whole affair protrudes through the hood. Since the scoop assembly is rigidly mounted to the engine, it vibrates noticeably while the engine is running, hence the “shaker” nickname. Shaker hoods fell out of favor for street cars with the end of the muscle car era in the early 1970s in large part because they make it difficult to meet noise regulations. Muscle car enthusiasts love them, though.
Duct Scoops – You’ve probably seen them on racing cars. They are a sort of reversed scoop buried below the surface of a car’s exterior with a gently sloped ramp and curved walls. These are often called called NACA ducts, at least in the US, as that was the Federal agency that developed them in 1940s for aircraft. NACA ducts don’t allow a high volume of airflow but they produce much less drag than other protruding scoops do.
Are you wondering why hood scoops aren’t more popular? Well, they have disadvantages too. First, functional scoops cost money to develop and implement. Plus, there are times you don’t want a scoop operating, such as during rainstorms and heavy snow. For non-performance automobiles, they probably just aren’t necessary. Today, you will find Duct Scoops quite popular on performance cars, though. Not only do they work nicely, they are a great styling touch also.
Source: Porsche Towson