Vengeance LPX 32GB 4x8GB CMK32GX4M4E4133C19

My motherboard is a GIGABYTE Z370 AORUS Gaming 7 with the latest firmware. The memory kit as specified in the Title is on Gigabyte's list of supported memory at 4133 Mhz.

The highest I can get is around 3925. I can't get anything over 4000 Mhz. Fortunately this kit allows me to have very tight timings, 17-17-17-38-625-2CR which I suppose might be better than 4133 with looser timings.

My memory is stable running MemTest86 with no errors. My question for any guru here is what is preventing me from achieving 4133? Upping voltages did not help. I even loaded the default profile in my UEFI and just selected the XMP Profile which resulted in a speed of 2133 or something around this.

Is it my motherboard? Could the XMP processing be faulty? Could memory training be involved. I'm more curious than complaining.

You probably already had to adjust VCCSA/IO and the subtimings for your 3925 CL17 setting? Then it is not a case of the board failing to apply proper voltages and training the sub timings. It could be the motherboard or processors IMC that is hitting its limit, with the former being more likely.

Did you try 4000/4133 with only two modules in the recommended slots? Maybe your board has a slot that is weaker than the others (sample variation).

You probably already had to adjust VCCSA/IO and the subtimings for your 3925 CL17 setting? Then it is not a case of the board failing to apply proper voltages and training the sub timings. It could be the motherboard or processors IMC that is hitting its limit, with the former being more likely.

 

Did you try 4000/4133 with only two modules in the recommended slots? Maybe your board has a slot that is weaker than the others (sample variation).

I didn't have to adjust any voltages to reach 3925. I had to do this by increasing the BCLK frequency a bit though. I managed to reach 3933 but I also had to up my VCORE a little. I haven't tried 2 DIMMS. IMO if 4x8GB is qualified to reach 4133 then it should.

Before I had this memory I had 64GB 4X16GB rated at 4000Mhz. They weren't a kit and are not on Gigabytes list. I was only ably to reach 3600 and a little change.

I read somewhere that my board has a single phase VRM(?) compared to boards that are dual phased. It was said that this is the problem.

In general DDR4-4000+ is way into overclocking territory for both your CPU and your board and as usual certain overclocks are not guaranteed. At the upper end the QVL is not the 100% definite answer that some people suggest it is. Sample variation is a real thing for CPUs and motherboards alike.

However since you did not adjust voltages, that is one thing you can still play with. VCCSA and VCCIO might have to be adjusted to your processors memory controllers needs. For both values too low and too high can prevent a successful POST or impact stability. Many boards actually tend to apply too much voltage at very high memory frequencies. So maybe start with the values used in your 3925 setting and then adjust from there.

If you think the memory VRM is too weak, that is one more reason to try again with only two modules installed, since it effectively halves the load on the memory VRM.

VCCSA and VCCIO are both set to ~1.30v via XMP. At 3900 I manually set them to 1.25v and I booted successfully into Windows 10. I haven't run Memtest86 yet. I guess 1.30v might be needed for 4133. DRAM voltage defaults to 1.4v. I set that to 1.35v.

I also raised and lowered VCCSA and VCCIO with RAM at 4000. Neither worked. I guess the other factors you mentioned are in play. I can't really complain. Based on the Passmark performance test I'm #1 on memory writes and #3 on reads or vice versa, I don't recall atm.)