Some guys build hot rods in their garage. Some guys overclock their PCs to ridiculously high clock frequencies (ahem… we might occasionally be guilty of this). [Nerd Ralph] decided to push an ATTiny13a to over twice its rated frequency.

It didn’t seem very difficult. [Ralph] used a 44.2 MHz can oscillator and set the device to use an external clock. He tested with a bit-banged UART and it worked as long as he kept the supply voltage at 5V.

Now, if you are just doing this for sport, a little liquid nitrogen will push your Arduino to 65 MHz

http://nerdralph.blogspot.ca/2015/07/externally-clocking-and-overclocking.html

At $1.5 a liter in Moscow, [Michail] couldn’t resist buying some liquid nitrogen for himself. He thought that because Arduinos were quite popular among geeks, he’d try to overclock one while bringing its temperature down to -196°C/-320°F.

It turns out that you can run an Arduino at 65.3MHz when it is cooled with liquid nitrogen!

Overclocking Arduino with liquid nitrogen cooling. 20⇒65.3Mhz @-196°C/-320°F
http://3.14.by/en/read/arduino-liquid-nitrogen-overclocking

What do you do when your project runs out of horsepower?
Well you increase them of course.

The Uno/Dumilanove Overdrive, running at 32MHz, makes your board and project go twice as fast.

It replaces the existing crystal with a clockgen running at 32MHz for twice the speed.