Running Arduino at 8MHz to Simulate ATTiny85 Internal

Is there a way I can (at runtime) turn the clock of the Arduino down to 8Mhz so I can experiment with running programs at low or high speeds? I do some projects with a microcontroller connected without a crystal, and I'd like to know if it has enough power to run something that I program on the Arduino.

I'd have to be able to slow the clock down and change the variables that affect the timing and delay functions. I want to develop on an Arduino because it's easier to wire things up and I don't have to mess with a programmer until I'm done with the project.

For example:

Create and debug a musical greeting card with flashing RGB light, 2 pins to a speaker (for 2-voice sound), and a button. 6 I/O pins. I'd develop it on my arduino.
Once it works, do a magic toggle and run it correctly at 8Mhz so I don't have to rewire my project onto another chip. Only when I'm satisfied would I burn it onto something like the AtTiny85 and disable the crystal and reset pins so I'd have 6 I/O pins.

Otherwise, I have to keep high-voltage programming the AtTiny to enable to reset pin so I can load a new program onto it. I'd rather keep the hardware-specific debugging to a minimum.

Thanks for any advice.

Look up clock prescaler in the datasheet.

Paul__B:
Look up clock prescaler in the datasheet.

I've seen examples of how to change the prescaler at runtime, but how would I change the other variables that control the delay, milis, and micros functions for timing? Can they be changed at runtime to match the new clock speed?

The LilyPad Arduino board entry may work.

If not, you will have to create a board entry.

shawnlg:
Only when I'm satisfied would I burn it onto something like the AtTiny85 and disable the crystal and reset pins so I'd have 6 I/O pins.

Develop on a Digispark or Trinket, where you can have 6 I/O pins on the ATtiny85, and revising your program and uploading happens via USB. To make a Trinket have the 6th I/O pin you can simply program the RSTDISBL fuse and it will still upload. Once you get the sketch finalized you can burn the hex file onto a stand alone ATtiny85 with a programmer.

Compile for 8mhz and set the prescalar in setup()