Overclocking Intel's Core i7 920 Processor
When overclocking your Core i7 processor, you really don't need a ton of BIOS flexibility with your motherboard, you only need to tweak a few key variables in order to unlock this architecture's potential. We did our overclocking on an EVGA X58 X3 SLI motherboard, which is a terrific overclocking platform, although the controls needed can be found on most shipping X58 motherboards.
1) Reference Clock - Core i7 processors have a base reference clock of 133 MHz, which is the key driver of many of the performance aspects of any Core i7 system. Processor clocks, memory clocks and QPI clocks are all driven off of this clock speed, so upping this ups all of these clocks together. If you want to get your 920 processor to 4.0 GHz, you'll need to crank up your bus clock to 200 MHz and manipulate a few clock ratios.
In our tests, this was possible on air-cooling, but difficult to retain stability. Our highest fully stable range was in the area of 190-195 MHz FSB, which allowed us to run our Core i7 920 processor (2.66 GHz) in the 3.8-3.9 GHz range. Keep in mind, Intel's top of the line shipping 965XE model only runs at 3.2 GHz, meaning you are outperforming Intel's $1,000 flagship by a significant margin, on a $300 processor.
Reference Clock Adjustments
CPU, Memory, QPI Voltages
2) Memory - If you're upping the reference clock, be sure to check your memory timings as well. Core i7 systems run their DDR3 memory speeds as a multiplier of the overall reference clock, and these are timed to allow for 800 MHz - 1600 MHz overall DDR3 clock speeds. Depending on the speed of your memory modules, it's likely that you will need to drop this multiplier down, so that when you up the overall reference clock, you don't overdrive your memory beyond its capability. If you downclock your memory multiplier, it's likely you won't have to rely on upping your memory voltage in order to get a sizable overclock.
3) Voltages - Core i7 systems typically don't show massive overclocking gains with additional voltage being thrown at them, but we found that for heavier overclocking, voltage levels of 1.3V and higher were helpful in retaining stability, whereas levels of 1.4V and higher typically did very little to help our overclocking situation. If you're doing heavy overclocking, voltage levels of 1.5V have been attempted and don't appear to hurt the chip, although long-term reliability at this level is certainly an unknown.
4) QPI and PCI Express - If you want stability at overclocked levels, be sure to kick down your QPI speed (which is also derived from the reference clock) to its lowest multiplier, typically labeled 4.8 GT/s (though you can try other setting to reach a top QPI speed with stability), in order to keep this area in check in an overclocked scenario. If your motherboard lets you, manually set the PCI Express clock to 100 MHz as well.
What to (Really) Expect
While we have seen some overclocking teams reach 4.5 - 5.0 GHz using off-the-shelf Core i7 920 processors, these kind of speeds are highly unlikely using home-brewed air-cooling or water-cooling setups. In order to reach these heights, you likely need to go into the LN2 or heavy duty water cooling setup areas. Here's what we think is possible for most end users out there using standard air-cooling systems.
3.2 GHz (stock voltage and cooling)
3.4-3.8 GHz (stock cooler, slightly raised CPU vCore)
(Likely requires third-party cooler and substantial CPU and chipset voltage boosts)
Likely requires liquid cooling or better, sizable voltage boosts.