In this instructables I will show you how to overclock a Raspberry Pi.
You don't need a heat sink or a fan, because the temperautre won't go over the 50-60 C (120-140 F).
Please vote for me in the Raspberry Pi contest.
Good luck with overclocking!
(!) I am not responsible for anything that happens because of this tutorial (!)

Step 1: Installing Raspbian

If you have already installed Raspbian you can skip this step.

For installing Raspbian you will need a 4gb SD card, a Raspbian raw image and Win32DiskImager (Windows) or dd command (Linux) or Rpi-SD card builder (Mac Os X).

Imaging the SD card

Windows

1. Download and install Win32DiskImager

2. Insert your SD card and open Win32DiskImager

3. Unzip the 201X-XX-XX-wheezy-raspbian.zip file (X is the date of your download)

4. Select the .IMG and select the correct device (!)

5. Now the SD card has the Raspbian Image

Linux

1. Start the terminal

2. Go to your downloaded .ZIP file

3. Use $ unzip ~/201X-XX-XX-wheezy-raspbian.zip (X is the date of your download)

4. Run $ df -h to see what devices are currently mounted

5. Insert your SD card

6. Run $ df -h again, the new device is your SD card

7. Unmount your SD card with $ umount /dev/xxxx (xxxx is your device)

8. Now write the image to your SD card with $ dd bs=4M if=~/201X-XX-XX-wheezy-raspbian.img of=/dev/xxx (xxx is your device)

9. The SD card has now the Raspbian Image

Mac OS X

1. Download and install RPi-sd card builder

2. Unzip 201X-XX-XX-wheezy-raspbian.zip file

3. Run the app and select the .IMG file

4. It will ask you if the SD card is connected, insert your SD card and press continue

5. Select your SD card

6. It will ask you to enter your administrator password, enter it

7. Look if your SD card is unmounted and press continue

8. After a while it says complete

9. Your SD card has now the Raspbian Image

Installing Raspbian on your Raspberry

1. Insert your SD card into your Raspberry Pi and connect your screen

2. Plugin your power, your Raspberry will turn on and boot Raspbian for the first time

3. You will get some options, you can skip them but I recommend that you select 1. Expand filesystem otherwise you will run out of memory and 3. Enable Boot to Desktop, I prefer the command line for overclocking.

4. Select finish, you will now be in the command line

5. Raspbian is now installed

Step 2: Installing Java, HWBOT Prime and OpenArena

Before we start overclocking we install two benchmark programs and java.

Installing Java

1. If you have already JDK7 installed remove it with $ sudo apt-get remove openjdk-7-jre
2. Use $ wget http://www.java.net/download/jdk8/archive/b117/binaries/jdk-8-ea-b117-linux-arm-vfp-hflt-20_nov_2013.tar.gz to download JDK8 (this one is only for ARM chips)
3. Now use the followning commands for installing: $ sudo tar zxvf jdk-8-ea-b117-linux-arm-vfp-hflt-20_nov_2013.tar.gz –C /opt then$ sudo update-alternatives –install “/usr/bin/java” “java” “/opt/jdk1.8.0/bin/java” 1 at last use $ java -version

Installing HWBOT Prime

1. To install HWBOT Prime you only need to download the .JAR with $ wget http://downloads.hwbot.org/hwbotprime.jar
2. Use $ java -jar hwbotprime.jar to run the benchmarks on the default specs.

Installing OpenArena

1. Run the following commands to install OpenArena: $ sudo apt-get install openarena then use $ wget http://www.berryterminal.com/dl/ioquake3_99.1.36-rpi01_armhf.deb and at last use $ sudo dpkg -i ./ioquake3_99.1.36-rpi01_armhf.deb
2. Now use $ sudo apt-get clean to remove the leftovers

Step 3: Overclocking

To overclock the Raspberry Pi you only need to change the config.txt. You can do this with your pc (the file is on the SD card) or with the command line

Editing the Config.txt with the command line

1. Go to the config.txt with this command: $ sudo nano /boot/config.txt
2. You will see a lot of options but you can skip the most of them, here is a list with the important options and there explannation:
frequency overclocking
arm_freq – ARM frequency, default = 700MHz
gpu_freq – GPU frequency, default = 250MHz
dram_freq – SDRAM frequency, default = 500MHz
core_freq – GPU core frequency, has an impact on ARM performance since it drives L2 cache
h264_freq – frequency of the hardware video block
isp_freq – frequency of the image sensor pipeline block
v3d_freq – frequency of the 3D block
Voltage overclocking
(!) The voltages can't be chosen individually, they will al be set to the lowest voltage (!)
(!) The minium is -16 the maxium 8, every step is 0.025 volt. The default is 0, with 1.2 volt (!)
over_voltage – ARM and GPU core voltage adjustment, default
over_voltage_sdram – sets all other SDRAM voltages together
over_voltage_sdram_c – SDRAM controller voltage adjustment
over_voltage_sdram_i – SDRAM I/O voltage adjustment
over_voltage_sdram_p – SDRAM phy voltage adjustment
3. You can use your mouse and keyboard to change the values
4. Exit with Esc and reboot your Raspberry Pi

Editing the Config.txt with your pc

1. Turn off your Raspberry Pi (unplug the power) and take your SD card
2. Insert your SD card into your computer and go to the folder Boot
3. Open the config.txt with your preferred text editor
4. You will see a lot of options but you can skip the most of them, here is a list with the important options and there explannation:

frequency overclocking
arm_freq – ARM frequency, default = 700MHz
gpu_freq – GPU frequency, default = 250MHz
dram_freq – SDRAM frequency, default = 500MHz
core_freq – GPU core frequency, has an impact on ARM performance since it drives L2 cache
h264_freq – frequency of the hardware video block
isp_freq – frequency of the image sensor pipeline block
v3d_freq – frequency of the 3D block
Voltage overclocking
(!) The voltages can't be chosen individually, they will al be set to the lowest voltage (!)
(!) The minium is -16 the maxium 8, every step is 0.025 volt. The default is 0, with 1.2 volt (!)
over_voltage – ARM and GPU core voltage adjustment, default
over_voltage_sdram – sets all other SDRAM voltages together
over_voltage_sdram_c – SDRAM controller voltage adjustment
over_voltage_sdram_i – SDRAM I/O voltage adjustment
over_voltage_sdram_p – SDRAM phy voltage adjustment
5. Now edit the values and reinsert your SD card to your Raspberry Pi

Step 4: Benchmarks

Now we're going to run two benchmark programs, HWBOT Prime and OpenArena.

HWBOT Prime benchmarks
1. Run $ java -jar hwbotprime.jar
2. Now compare your score to your previous score
OpenArena benchmarks
1. Run $ sudo /usr/games/openarena to launch OpenArena
2. Press ~ to launch the console
3. Type the following things into the console: timedemo 1 (to enable benchmarking) then cg_drawfps 1 (to show the amount of fps) and demo demo001_test1 (to load the map).
4. Your FPS is your score.

Step 5: My Configuration and Benchmarks

Because a few people asked for my configuration and benchmarks I added a extra step with my configuration and benchmarks

Config.txt
I edited the following things in the config.txt:
arm_freq=1200
gpu_freq=355
core_freq=710
h264_freq=250
isp_freq=250
v3d_freq=250
sdram_freq=680
over_voltage=8
over_voltage_sdram=6
over_voltage_sdram_c=0
over_voltage_sdram_i=0
over_voltage_sdram_p=0
disable_l2cache=0
force_turbo=1
temp_limit=85
avoid_pwm_pll=1

Benchmarks
568.6 primes per second with HWBOT Prime
16.2 frames per second with OpenArena