Ever wondered how those zokushas have that sharp high pitch when revving their engines like this?

The principle is very simple: normal exhausts have mufflers which silence all sounds whil most aftermarket exhausts will silence all high tones to give that deep bass sound. To get the high note like the zokushas you need to do the reverse:

How to create a bosozoku style high pitch muffler

First take an exhaust with the widest pipe (to lose least sound as possible).

How to create a bosozoku style high pitch muffler

Then add an extra sidepipe which will silence the deep bass sounds.

How to create a bosozoku style high pitch muffler

If needed add another to silence the mid tones.

How to create a bosozoku style high pitch muffler

And mount it under your favorite zokusha!

Found on Mario's site