Motorcycle Airbox Component - Air Force

Thankfully, in these tough times there's still plenty of air to go around. Gas may be over three bucks a gallon, but nobody has worked out how to charge for air (or tax it) yet. But why, when air is all around us, does a bike need a special box for the stuff? A box full of air? It wouldn't make a very good birthday gift...

And it's such a big item. Most current sportbikes have replaced the "fuel tank" that used to sit under the rider's chin, in front of the seat, with a massive airbox. The latest Suzuki GSX-R1000 airbox holds 8.5 liters-that's more than half the size of the fuel tank.

The airbox has a range of small, janitorial tasks to perform-the most obvious one is to hold the air filter. You have to keep grit and dirt out of the engine or it will quickly wear the bores away. Ditto water and small rodents. A piece of foam or cotton paper will do the job, and as long as the design has enough surface area to flow all the air that the engine needs at peak power, it's all you need.

It also acts as a receptacle for a number of small, noxious outputs: the fuel tank breather pipes, any carburetor breathers, and finally the crankcase breather pipe. This breather in particular contains combustion gases that have leaked past the piston rings along with a mist of hot, stinky engine oil, so it's fed into the inlet tracts. Finally, an airbox will act as a silencer for intake noise, helping the bike pass those pesky noise regulations.

These mundane tasks were originally all that the airbox had to do. But when real sportbikes began to appear in the mid 1980s, engine designers realized there were performance gains to be had from a more careful airbox design. Like exhaust systems, a clever airbox can give a broader spread of power from an engine, improve bottom end delivery, and even add "free" horsepower at the top end.

There are three main ways of doing this. First is by optimizing the air flow into the engine. Hot air is bad for making maximum horsepower since it's less dense than cold air. Less density means fewer oxygen molecules in each liter of air; less gas can be burnt, making less torque and power. So, if an airbox has its inlet at the front of the nosecone rather than right next to the super-hot radiator or exhaust pipes, it'll get more oxygen in and more power out.