Taking Q8400 to the next level


Sep 13, 2009

I have overclocked my Q8400 to 3.0 GHz (from stock 2.66 GHz).

I ran Prime95 (blend) for 29 hours without errors and 3DMark06 ran fine as well. Temperatures during Prime95 was max. 51 C on any core (according to CoreTemp and SpeedFan).

I was just wondering what the next step would be if was to push my CPU further. That is - what kind of speeds would be the 'max' given my settings and hardware specs below. The purpose of overclocking for me is better gaming performance, so I'm not really in it for the overclocking itself (although I admit it's kind of fun :) ).

BIOS settings:
Vcore 1.31250V
FSB 1500 MHz
Memory 900MHz (linked)
Multiplier x 8.0

PC specs:
Intel Core 2 Quad Q8400 2.66GHz 4MB 1333MHz @3.0 GHz
ZEROtherm High-end CPU Cooler BTF90
ASUS P5N-D NForce 750i SLI PCI-E
Corsair 2x2GB DDR2 XMS2 PC6400
XFX Geforce GTX 260 896MB GDDR3 PCI-E
ACE Raw Deal +620W
ANTEC Midtower Three Hundred
320GB Seagate Barracuda 7200.11 SATA-300 16 MB
Windows XP 32-bit SP3

Any suggestions/tips/tricks are much appreciated! :)
You are overclocking your memory (FSB freq = 375 MHz, mem clock at 900 MHz instead of 750 MHz. memclock at 900 MHz puts it past DDR2-800. Max core temp indicates that you can push the CPU harder.

Run your memory at 1:1 (mem clock = 2 X FSB frequency. I think that you can reach 3.2 GHz ( 8 X 400 MHz).
Overclocking since 1978 - Z80 (TRS-80) from 1.77 MHz to 2.01 MHz


Sep 28, 2009
Hi guys,

i have bought for a week this cpu and would like to overclock it in the next time :) but i havent ideas how it is work? :) can you give me some guide how i can do it. my mainboard is a asus p5q pro without firmware update. and i have a cpu cooler from alpenfoen.

thanks forward :ange:


Apr 10, 2009
+1 for jsc

with ddr2 800 memory run at 1:1 and try 400fsb x8 cpu multiplier

alot of boards get flaky above 440-450 fsb not sure how yours is.

but 8x 400 is a decent overclock.


Sep 13, 2009
Hi again,

Sadly I'm not making much progress going beyond 3.0 GHz... It seems that running my memory on anything lower than 900 MHz results in my pc not booting properly. (that is when attempting to go above stock 2.66 GHz)

I've tried the 1:1 settings (1600 FSB / 800 MHz memory) but I didn't get it to work. After I 'save and exit' in BIOS the pc doesn't boot and I have to turn it off and on again. Then it goes through POST but gives me a message about the last boot or POST was a failure, and I am prompted to go into BIOS and revert back to default settings or press F1 to continue. The latter lets me boot all the way into Windows but looking in CPU-Z all settings have been changed back to stock values (2.66 GHz etc etc).
On the other hand, if I choose to go into BIOS I see that all settings are still at the o/c values but exiting without saving results in either a proper boot (but still nothing higher than stock values in CPU-Z) OR "nothing" happens... (which forces me to turn the pc off and on again).

Going back to my 3.0 GHz settings (as described in my first post^) works fine and boots and POSTs without error everytime.

Do I need to apply more Vcore voltage or start messing around with my memory voltages/timings to be able to reach higher speeds? (never done that before).
And can someone please explain "sync mode" ? :)

As always, any help is greatly appreciated!