Watch the youtube video of this guy and you will get there. Be patient, it really works! I left out the obvious like tools, thermal paste and cleaning and prep.

The trick is not to panic when things go wrong. I paid $370 for the Processors and now my Geek Bench is slightly over 26,000 - that's pretty much double my 2.26GHz 8-core. Follow this guy's (youtube video) tips: 'Mac Pro 2009 CPU upgrade 8 core Nehalem to 12 core Westmere'. If your heatsink fan connectors don't seat far enough down you will never post.

I used a small mirror to look into the heatsinks and made sure the fans were spinning. So I took out the second nylon washer on each screw and made slight equal tight and loosen adjustments and after several attempts it finally posted as a 12 core Mac with 24 gigs RAM. After many more adjustments of B CPU heatsink it still would not POST. I then made very slight adjustments to CPU heatsink A and the lights went out but when I checked my 'about this Mac' it saw only the A CPU. The fan speed was normal but I had red lights on the CPU board. The fans on CPU A were at full speed and no matter what adjustments I made they stayed at full speed until I put in CPU B.

I replaced the second washers with one's half as thick and now it posted with the 3 sticks of ram. I had a problem POSTing ( Power On Self Test), so when I looked closely at the processor under the heatsink I noticed it wasn't down cleanly on the socket. I put in (2) 1mm nylon washers on each heatsink screw and slowly tightened them down first on processor A only. ( Ref: Intel's X5670 specs.) I read everything I could find but so many things can go wrong. I finally got my nerve up to buy a matched pair of used X5670 2.93GHz CPUs. ( Mac Pro (4,1) updated to (unofficial) MacPro5,1 EFI for 6-core CPU support) ( First report, ) ' 2009 Mac Pro 12-core CPU Upgrade - Dual x5670 CPUs (Updated Aug 21st, 2015 - archived guide link pulled) Using Dual Xeon X5670 or X5690 Westmere CPUs Report/Tips: 2009 Mac Pro 12-core CPU Upgrades Mac Upgrades/Repairs | Storage | Video & Displays | Audio/Home Theater | OS Updates/Tips/Wi-Fi 2009 Mac Pro 12-Core CPU Upgrades using Dual X5670/X5690 6-Core CPUs and Mac Pro 5,1 bootrom

8 core mac pro upgrade