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Overclocking Q8400

Last response: in Overclocking
July 2, 2009 1:26:15 AM

I have overclocked my Q8400 to 3.3ghz so far but want more but every time i raise the fsb it either freezes at the post message or doesnt boot up. i have left the Vcore on auto as i dont understand the way my board works it says +0.50 or somthing like that i really need help. Also is it normal for my CPU to be running at the same temperature as it was on stock?

Intel Core 2 Quad Q8400 2.66ghz @ 3.3ghz
Asus p5kpl/1600
Thermaltake V9
2x 1gb Infineon 667mhz RAM
Codegen Technology 600w PSU

More about : overclocking q8400

a c 172 à CPUs
a c 197 K Overclocking
July 2, 2009 9:28:00 PM

As long as the voltage applied to the CPU has not increased, the temperatures pretty much will not either.

Install CoreTemp. Then run it. You will see a setting called VID. That's the default voltage for the chip. Lower is better. Intel's max voltage for a 45 nm CPU is 1.3625 volts. Subtract your VID from that. The difference is how much you can overvolt the CPU.

Set your BIOS for the VID. Run the FSB up until the system is not stable. Increase the voltage a little, then increase the FSB. Test. Repeat until vcore reaches 1.3625 volts or the temps reach 70 C.
July 3, 2009 1:25:56 AM

By keeping it set to auto does it actually change or stay the same.
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November 26, 2009 4:40:38 PM

I have the same Q8400 CPU on an eVGA 750i SLI m/b, and I managed to get it to where I can run with the settings on manual with 1333 FSB and 1.2250v for the CPU core, but as soon as I try to increase it above 1333, like even 1375, I can't boot. I tried increasing the CPU voltage one notch, but still no boot.

Any suggestions how to go about this? Almost every time I just get a black screen and then I need to power it off, clear CMOS, and start over, and I haven't been able to get above 1333 it seems no matter what I try.

VID is 1.2250

thanks if anyone could suggest...
December 10, 2009 4:17:54 AM

hey guys i too am having a prob OC my 8400.. but i think its somthing to do with my ram ratio
when i run it 3:5 i can only get to 3.0 ghz stable.. and of course my fsb is way lower than say
when i run it at a 1:1 ratio and so far my settings for that are a 1921 fsb 2000 is my max which i have run before
core speed is now 3361.7 mhz also mulitpler is at 7

fsb 1920
ram is 1:1
bus 480 mhz\
multiplier is 7

btw my ram is ddr2 1066 so im right under that 1066 mark

corev is 1.280 all stock i havent changed..
i did have to change when i got to 3.5 ghz only slightly but i decided to jsut run at 3.3 and keep voltages stock
December 10, 2009 8:11:26 AM

I tried the Asus AI overclocking, and can get 10% from it, but I'm surprised thats all I can get. I realized that my CPU is actually a Q9400, not Q8400, but I think the same theory would apply, because I've also now used it on my E8600 to get it stable at 4.00 ghz.

I found someone on the Asus board that appears to be a guru who said to:

Overclock motherboard first
then overclock CPU
then overclock memory

I am certainly no expert, but this worked for me. Gurus are free to suggest or criticize. Had I had better instructions to go on, I might have done better.

HOW TO OVERCLOCK an ASUS P5N72-T PREMIUM with Core 2 Quad Q9400

I managed to get 3.13ghz from it. 1600 fsb was just too much a stretch for the motherboard, so I just couldn't get 3.2ghz to run stably, so settled on 1566 and resulting 3.133ghz.

worked on m/b 1st
Started by reset to defaults
disabled spread spectrums, whatever they are
changed multiplier to 6, FSB to 1600 and memory to 600 unlinked
worked PLL to 1.64
worked VTT to 1.40
worked NB to 1.44
tried all possible values on SB, but runs fine on Auto at 1566

then worked on cpu
worked multiplier to 8.0
worked CPUv to 1.33750

then worked on the memory
linked/synced @ 783
now testing linked/auto @ 939.3

When I say worked, I mean a test run with each setting from a lowish number to the highest before it gets worse, then I'd back off by 1 and go to the next setting, trying to get 1 hr on prime95 for each without any errors. used small fft to test m/b and cpu, blended test for memory. I'm now at where I kill the memory test with no errors after 4hrs.

basically, the m/b didn't do so well compared to my evga 780i as far as FSB capability, but the smartfan makes it a LOT quieter in real world daily running, but its running stably at 3.133ghz which is a lot better than the 2.93ghz best the AI (automatic overclock) program would give me.
December 10, 2009 11:59:38 PM

so im wondering why u barely got any overclock considering the Q8400 and Q9400 are identical beside the bigger l2 cache on Q9400.

so i wrote down my settings as i tried to overclock to 3.5 ghz
as of now everything is stock voltage
coreV is 1.280
multi is 7 x 498 bus = 3487.4 mhz or 3.4 mhz
rated FSB is 1980 my mobo can handle up to 2000 Asrock P45xe
fsb:D ram is 1:1
ram is at 400 i believe around 900 ish my ram is capable of 1066 tho..

so now my question is how come mine over clocks so ez on stock voltage?
only thing i can gather from this is my huge FSB my mobo can handle ..
but when say i try an
8 x 400 = 3.2
3:5 FSB:D ram ratio
core v 1.28
ram is set to 400 1066

for some reason i believe the ram ratio is causing my system unstability because im pushing it alot harder on a 3:5 than a 1:1 ratio..

now the question is, does that mean a higher FSB overclock is better than a higher multiplier over clock?
im confused
December 11, 2009 2:08:34 AM

I couldn't run 400 FSB without getting errors and crashes even with the multiplier set at 6 and memory unlinked at 600 on auto settings
December 11, 2009 2:58:55 AM

so im confused a bit... what does memory unlinked and auto mean?

like for me for instance i have mine set at 400(9ish) or i can choose 200(???) or auto which i believe sets it at 333(???)

so what does unlinked mean? does it mean u manually select the bus speed? which i did for my overclock btw
December 11, 2009 4:04:25 AM

you want it as high as you can get and still be stable, imo
December 11, 2009 4:12:37 AM

well yeah i understand that, im jsut a bit confused on the ram thing
what does memory unlinked and auto mean?
December 11, 2009 4:41:19 AM

I'm no expert, but if you link it, the bios will choose or allow you to choose among the best combos of timing for them to talk to each other. If youu pick it manually (unlinked), you probably want it to be at some ratio to the FSB and therefore CPU.
December 11, 2009 4:50:52 AM

wow maybe i need to read that oc manual again cause maybe im not describing my situation correctly either way im at 3.4 ghz stable.. i jsut read on newegg of guys getting up to 4 ghz.. i want to reach close to that...
December 11, 2009 7:40:27 AM

ok so i did some more OC testing and found out that the q8400 doesnt like to be pushed past the 3.5 range... i did manage to get into 3.75 range but it was BSOD after a min... that pretty much was the range of my fsb anyway 2002..
so now im realizing that it takes alot of core juice to get these things to run stable..
unles im wrong and that it takes more juice and more power to the NB cores.. but i have those set to auto , so should make no difference. the point is that the cpu needs alot of juice past 3.4 ghz so for me im sticking with a modest 3.3 OC on stock voltage. i jsut feel like the gain is not worth the stress.. or heat

heres my settings 7 x 475 = 3328 or 3.3 mhz
dram 475 ddr2 950
fsb to mch strap is 400
core V is 1.268
fsb 1902..
ram ratio is 1 to 1
i may jsut go up to 3.4 ghz and leave it there..

i also did a bunch of tests on 7.5 multiplier and that works equally wel with a 1 to 1 ram divider for those who dont have a high FSB mobo like i have

again 1 to 1 ram divider was the only way i was able to get to 3.4 stable
3 to 4 divider for some reason just gave me blue screens and couldnt get past 3.2 ghz..
December 11, 2009 1:16:53 PM

You didn't say what m/b you have, and that determines FSB limits, I think. On my Asus P5N72-T Premium with Q9400, I boosted VTT and NB a bit last night and it seems to be ok with 1700 now, but I'm only 1 hr into prime95 with it at the moment, and it wasn't BSOD till 2.5 hrs before, so it will be a while before I know if those were why I wasn't able to get to 1600 before.

What manual?
December 11, 2009 7:14:12 PM

the manual is here

as for my mobo its Asrock P45xe

has a 2000 fsb .

for me all my nb, vtt sb, cores are all set on auto.. which i think helps in the beggining to rasie ur speed, but should be dialed down once u can get stable. and then lower the juice to them for power savings and stabilty..

but for me its fine at auto :)  and my core V is at 1.287, and thats what the chip runs at stock i believe
December 12, 2009 7:07:15 AM

I got the Asus stable at 3.4ghz (28% OC). It took another long day of effort to get it there. It took more cpu, NB, SB and HT voltage, and more relaxed memory timing to get it.

Looks like I got the eVGA 780 doing a bit better, too, now up to 4.125ghz (24% OC). I just couldn't seem to find settings that would work for more than a few seconds in prime95 at 1700 FSB with it, so I had to back it down a bit to find stability.

Thanks for the link to the manual. It wasn't the method I used exactly, but the change one thing at a time method was consistent with what worked for me.
December 12, 2009 6:57:43 PM

wait did i miss something here?
evga 780 is 24 % oc with what processor? Q9400?
asus is 28% OC with what processor?

anyway if i assume corectly u OC the q9400 to 4.12ghz? wow thats insanely high

even on my q8400 highest i got was 3.75 and even then it would bsod on prime 95 tests.

but anyway im try and mess with the core voltages so that they are not all on auto..

December 12, 2009 10:13:50 PM

the eVGA has a E8600 Duo, stock 3.33, running at 4.12. Still getting rounding error after about 4 hrs on prime95.

my Asus has a Q9400 Quad in it, stock 2.66, running at 3.4. prime95 doing fine for 5 hrs, but had one immediate application crash, so may have to back it down a tad.
December 13, 2009 5:26:41 AM

ahh i see yeah i read somewhere that the quads or 45 nm chips dont take well to voltage, which makes them bad OC.. but hey 2.66 to 3.4 is not bad tho and honestly the speed is good already with a quad core
December 13, 2009 7:37:57 AM

The Quads are good if you have applications that will make use of more than one or two cores. I took a Q9450 Quad out of the eVGA 780i and replaced it with the E8600 Duo because the applications that machine is running only seem to use 1 or 2 cores at a time, anyway, so getting the 4.12ghz out of the Duo gives me better performance than if I'd gotten 3.4ghz out of the Quad that was in it.

What to do with the leftover Q9450 from that one is another question, LOL. I guess I should sell it or build another computer out of all my excess parts laying around.
December 13, 2009 2:19:15 PM

yeahi think my mis take was buying a quad because of the lack of multi processor support on apps... but im happy at 3.4 i mean im upgrading from a centrino 1.7 notebook.... this quad is tons faster than im used to... heh although now i want to get an i5 .. too late for that now
March 28, 2010 5:45:22 AM


Q8400 + EP43T-UD3L + Coresair XMP 1600 3x1gb

fsb = 419
ram = auto

cpu v = 1.212
dram v = 1.50

it stuck at 3.35 and can't more than this
i want mine rise up to 3.5 (at least)
but i can't at all the ways
March 30, 2010 7:08:38 AM

rasak said:

Q8400 + EP43T-UD3L + Coresair XMP 1600 3x1gb

fsb = 419
ram = auto

cpu v = 1.212
dram v = 1.50

it stuck at 3.35 and can't more than this
i want mine rise up to 3.5 (at least)
but i can't at all the ways

I can OC my Q8400 to easily, FSB=444 * 8 = 3.55Ghz... Vcore = 1.2975
NB voltage = +.075
FSB Voltage = +0.1

My ram is Corsair Dominator PC8500
Ram Voltage = 2.1

U can increase your NB & FSB voltage.
a b à CPUs
a b K Overclocking
June 13, 2010 7:49:47 AM

I manged to get my Q 8400 to 3.6 ghz stable with P45 MSI board, but i generally use a 3.2 or 3.4 oc because of high temps on 3.6. I don't want temps over 70 -
Maybe with failed oc , u can flash the jumper on the board[ depending of boards options] while pc off. It, will definitely boot on normal settings.
Btw, 3.2 ghz is just fine for a Q 8400 with a cooler, max load temps under 65 c
June 15, 2010 6:44:45 AM

Hi there,

I currently have a q8400, deciding on which mobo to buy. Was thinking of getting an AsRock P45X3 Deluxe cause I read reviews people pushing it to 4GHz with ease with a midstream cooler. But seeing you guys all have trouble pushing it above 3,4 GHz, think I´ll stick with the P5KPL/1600. What do you think?

Just one thing: none of you mentioned which cooler you´re using. Are you all on intel´s stock coolers?

a b à CPUs
a b K Overclocking
June 15, 2010 2:38:04 PM

I have a Hyper 212 + cooler-
I manage to get to 3.6 ghz , but on continuous full load it will reach over 70 ..
But its still fine, but i just keep mine at 3.2 ghz, no overheat prob, and temps stay under 60 c.
I currently have a P45 MSI Neo 3 fr board.
a b à CPUs
a b K Overclocking
June 21, 2010 7:32:21 AM

I managed to get 3.6 ghz -
Dont let your mobo on voltage on auto , use 1.31 volt.
Oc 3.6 ghz w.o prob and temps will be fine on 60 c with a good cooler or even less.