Over Clocking q9400

Not very much at all. Maziar is right. There are a lot of variables, some based on your choices and some based on the luck of the draw.

But you specified the stock Intel heatsink. The heatsink that comes with a 2nd gen C2 such as an E8400 or Q9400 is half the size of the heatsink that came with a 1st gen C2 such as an E6600 or Q6600. The larger heatsink meant that you had a good chance of reaching a 25% OC with stock cooler. The newer heatsinks are just large enough to run safely at stock speed.

If you can find a 1st generation cooler, you have a pretty good chance of getting a 20% OC - assuming that your motherboard will let you and your power supply will let you and you have a decent case.

If you get lucky and get a CPU with a pretty low VID, you should be able to reach a pretty good OC. If you do not know what VID is, you need to do some homework.

Two guides:

HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1
http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guide

Core 2 Quad and Duo Temperature Guide
http://www.tomshardware.com/forum/221745-29-core-quad-temperature-guide

Keep in mind that these are guides, not cookbooks.
 

cadder

Distinguished
Nov 17, 2008
1,711
1
19,865
I would not attempt an overclock with the stock heatsink unless I already had it all built and wanted to do it as an experiment. If I was serious about using the machine in overclocked state I would get an aftermarket cooler first.

I have a Q9400, I installed it with a Xigmatek 1283 cooler. I experimented with mine at 3.76MHz and it looked like temperatures were going to stay below 50C.