Backpressure and Other Types of Mufflers
The exhaust from a NASCAR race car: There are no mufflers here, because reducingbackpressure is the name of the game.
Diagram of glass pack muffler
An important feature of mufflers is how much back pressure they produce. Due to all the turns and holes that the exhaust has to go through, the muffler in the previous section produces a fairly high back pressure. This subtracts a little from the power of the engine.
There are other types of mufflers that can reduce back pressure. One type, sometimes called a glass bag or a cherry bomb, uses only absorption to reduce sound. On such a muffler, the exhaust gas passes directly through the perforated pipe. This pipe is surrounded by a layer of glass insulation that absorbs some pressure pulses. A steel housing surrounds the insulation.
These mufflers produce much less restriction, but don't reduce the sound level as much as conventional mufflers.