combustion is what makes your car move at all. Read
http://auto.howstuffworks.com/engine.htm, it will tell you all about a car engine and how it works. Also, as far as the adapter, no it is not the pipe. I forgot you have an SL. If you go to
http://www.3sxperformance.com/intake.asp
and take a look at their pictures, the 2nd picture down shows the filter and adapter, the 4th shows the pipe that you would need, being that you own an SL. I have hte vr4, so I don't have room for the pipe to fit under my hood, its too crowded. So if you got the K&N FIPK, for example, you would get a pipe and the air filter, and probably not get the adapter, I on the other hand, need the adapter. Hope that explains it all.