i7 920 c0 overclock to 4.0gHz - need help with ram issues

Little background on my rig:
i7 920 @ 4.0gHz on an Asus P6T Deluxe mobo
Corsair H80 Hydro CPU cooler
12gb of Corsair Dominators (model TR3X6G1600C8D: stock clocks: 8-8-8-24 1600mHz -whatever this means! haha)
Corsair 1000w power supply
2x Sapphire 6950 2gb unlocked to 6970 bios
Antec 1200 case

Last night I was able to run prime95 small FFT for 9 hours with no errors (which I'm told stresses CPU only) but fail at the blend stress test at about 1 hour into it (told this stresses both CPU and Ram heavily) thus I've concluded its a memory issue? I'm guessing it deals with timings and/or voltages to ram but Ram timings confuse me so I'd like to get some help from some of you!

At 100% load my cpu doesn't reach above 75C which I'm fine with and idles around 38-41c

My overclock settings in Asus P6T bios are as follows:
Ai Overclock Tuner: manual
CPU Ratio Setting: 21
Intel SpeedStep Tech: Disabled
BCLK Frequency: 191
PCIE Frequency: 100
DRAM Frequency: DDR3-1531 MHz
QPI Link Data Rate: Auto

CPU Voltage: 1.36875V
CPU PLL Voltage: Auto
QPI/DRAM Core Voltage: 1.35V
IOH Voltage: Auto
IOH PCIE Voltage: Auto
ICH Voltage: Auto
ICH PCIE Voltage: Auto
DRAM Bus Voltage: Auto
DRAM DATA REF Voltage on CHA: Auto
DRAM CTRL REF Voltage on CHA: Auto
DRAM DATA REF Voltage on CHB: Auto
DRAM CTRL REF Voltage on CHB: Auto
DRAM DATA REF Voltage on CHC: Auto
DRAM CTRL REF Voltage on CHC: Auto

Load-Line Calibration: Enabled
CPU Differential Amplitude: 800mV
CPU Clock Skew: Auto
CPU Spread Spectrum: Disabled
IOH Clock Skew: Auto
PCIE Spread Spectrum: Disabled

C1E Support: Disabled
Hardware Prefetcher: Enabled
Adjacent Cache Line Prefetch: Enabled
Intel Virtualization Tech: Disabled
CPU TM Function: Disabled
Execute Disable Bit: Enabled
Intel HT Technology: Enabled - (thinking about disabling to reduce temps as I don't think this really affects gaming? your thoughts?)
Active Processor Cores: All
A20M: Disabled
Intell Speedstep Tech Disabled
Intel C-State Tech Disabled





So that is what I've figured out thus far on my own. This is my first time ever overclocking and majority of this goes over my head especially when it comes to ram, but I've gotten this far and would like to be able to make this stable if possible! I really appreciate all of your help!

Josh

Change the following...

CAS# Latency: Auto to 8
RAS# to CAS# Delay: Auto to 8
RAS# Pre Time: Auto to 8
RAS# Act Time: Auto to 24

DRAM Bus Voltage: Auto to 1.65V

... and leave all of the sub-timings on Auto. Bump QPI/DRAM Core Voltage from 1.35V to 1.45 - 1.50V. In order to run 12GB of DDR3-1600 stably at DDR3-1531 or higher on a P6T-D, it's usually necessary to bump the VTT (QPI/DRAM Core) higher than the "absolute maximum" of 1.35V that Intel recommends for the 900 series of chips.

redduc900 said:

Change the following...

CAS# Latency: Auto to 8
RAS# to CAS# Delay: Auto to 8
RAS# Pre Time: Auto to 8
RAS# Act Time: Auto to 24

DRAM Bus Voltage: Auto to 1.65V

... and leave all of the sub-timings on Auto. Bump QPI/DRAM Core Voltage from 1.35V to 1.45 - 1.50V. In order to run 12GB of DDR3-1600 stably at DDR3-1531 or higher on a P6T-D, it's usually necessary to bump the VTT (QPI/DRAM Core) higher than the "absolute maximum" of 1.35V that Intel recommends for the 900 series of chips.

Click to expand...

Already had DRAM Bus Volt to 1.66v and not auto.
I've set QPI/DRAM Core to 1.45625v - and got it to run blend for ~2hrs b4 crashing and increasing it one more tick causes crashing soon after starting stress test...

Anything else I should change from auto to something?

I've seen a lot of people changing PPL from auto to 1.8-1.9v but I have no idea what this is. Also what about north/south bridges (IOH/ICH voltages?)

Here is a screenshot of my prime95 blend run @1.45625v on QPI/DRAM Core (VTT) - cant figure out what any of this means haha

I have actually decided to decrease my QPI back down to 1.35v as I felt 1.4+ was unsafe. I did however, manually adjust my memory timings to 8-8-8-24 as you suggested.

I upped IOH to 1.2v, ICH to 1.2v, PPL to 1.88v, and CPU clock skew to 300ps

I have also after doing some reading have turned hyperthreading off as it drops my temps from 73-78C to 63-70C, and doesn't really affect many things I do.

I am currently running @ 4.0gHz on my c0 i7 920 (1.36cvore) with 9 hours of small FTT testing on prime and about to hit 8 hours of custom blend with 95% memory usage! I think this is fairly stable. Thanks for you help with the memory issue! I think that is what my initial problem was.

does 9-9-9-24 to 8-8-8-24 really make a big difference? I can't find any info on exactly what this means

mikeyw said:

does 9-9-9-24 to 8-8-8-24 really make a big difference? I can't find any info on exactly what this means

Click to expand...

Well I'm not the person to ask but in my case it seemed like that helped. I know my ram was rated at 8-8-8-24 so I don't know if on auto which set it at 9-9-9-24 made the issue of instability but after setting it manually everything seems to be running smoothly. I guess it being underclocked caused instability. Correct if I'm wrong but I've been told lower numbers means it's faster? I also did other changes as well such as ppl volt and ioh(NB) volt increases. See two posts above.