Allgemein GPUs Hardware Practice Reviews Watercooling

Unleashed unicorn on a flight of fancy – Shunt-Mod for NVIDIA GeForce RTX 3090 FE and the Alphacool Eisblock GPX-N | Practice

Test results

The test system and methodology are identical to the previous article, which you can find here for reference. But briefly summarized again: The 3DMark Port Royal benchmark is run in loop mode for 10 minutes at a time and the monitoring data is collected via HWinfo. In addition, the graphics card was overclocked based on the maximum that was stable with the Founders Edition stock cooler and then the same settings were compared in the modified state. So again the OC setting is + 100 MHz GPU, + 1000 MHz memory, + 15% power and 90 °C temperature limit.

If we first look at the overall power consumption of the graphics card, the mod immediately catches the eye. Where previously 115% of 350 W with an effective 400 W was the hard limit, current can now flow almost unhindered and thus power can be consumed. Without changing any setting in MSI Afterburner, the card now automatically allows itself 80 W more.

Due to the shunt mod, there is even some more room for overclocking, so that another 50 MHz more at the GPU and 400 MHz more at the memory run stable. However, with this “extra OC” setting, the RTX 3090 in ITX format already allows itself just under 500 W. And that’s only the average, mind you, the spikes should happen far beyond 600 W. 

Shortly to explain how I come to the power data with shunt mod, where the monitoring of the GPU shows much less consumption according to HWinfo: The calculation of the current and power consumption based on the known shunt resistance value can now of course also be applied backwards. And so we find an average TGP of 279 W in the log, but we know to multiply it with the factor 5/2.92 to get the real power consumption. The result is then the 478 W as highlighted in pink in the diagram.

In addition to a considerable jump upwards, there is also a remarkable outlier in the other direction in the clock rates, which I would like to discuss first. While the RTX 3090 without the shunt mod minimally clocks back to 1695 MHz on the GPU at idle to save power, the minimum clock rate with shunt mod drops to a tiny 210 MHz. After a little research I was able to find out that the 210 MHz is actually the correct idle behavior for Ampere cards, and the 1695 MHz as I measured it out of the box is actually incorrect or not intended by Nvidia.

The reason for this error is apparently a bug in the graphics driver in topologies with more than one monitor connected, where the graphics card never switches from 3D mode to 2D mode and therefore never reaches true idle mode. By doing the mod, we allow the card to stay in 2D mode, even when 2 monitors are connected. If you have an Ampere card and have more than one monitor connected, I’d be interested to know if you see the same phenomenon. Feel free to let me know on the forum. So with the shunt mod, we’ve even revived idle mode with maximum power savings – a positive, if unexpected, side effect.

Now let’s get to the elephant in the room, the clock rate under full load. While the GPU still jerked up and down without the shunt mod and permanently scratched at the performance limit, an almost perfectly constant clock rate is now available with the shunt mod. Without changing any setting and with the same + 100 MHz offset, the GPU now reaches 2085 MHz over the entire duration of the benchmark run after a few seconds of startup phase. That’s about 100 MHz more than before the mod with the Alphacool Eisblock, which itself is already on average 100 MHz ahead of the Founders Edition cooler. With the gained free heardroom, even 2160 MHz can be operated stably as the “extra OC” setting.

When we look at the actual benchmark results of 3DMark Port Royal, the gain in performance is also immediately apparent. We now get around 500 points more in the benchmark score for the 80 W more power consumption. In percent, that’s 3.6% more performance for 20% more power consumption. Well, efficient is different and here it becomes well visible why Nvidia sets a performance limit for the boost algorithm in their graphics cards to improve the efficiency significantly. But if you’re looking for maximum performance at any price, you’ll even manage to crack the 15000 point mark with the “extra OC” in GPU and memory.

Of course, the additional power consumption must now also be dissipated by the graphics card in the form of heat. Here you can see the previously pink highlighted setting with “only” + 100 MHz on the GPU and + 1000 MHz on the memory, as already tested with the Founders Edition and Alphacool Eisblock GPX-N cooler alone. Here, the delta of GPU to water temperature now rises to an average of 20°C, GPU hotspot and memory settle at 33°C and 45°C respectively. If you consider that now almost 480 W are dissipated here, but the loop with 65% pump speed is almost inaudible, the Alphacool Eisblock does a very good job even despite shunt mod!

Conclusion

A maximum of 11.3% performance gain has now been achieved by upgrading to the Alphacool Eisblock in combination with the shunt mod. On the side of the counter-arguments are the 25% higher power consumption and of course the residual risk of damage up to a complete defect of the GPU. Reasonable this is not, of course, but reason literally left the chat when we bought the RTX 3090 Founders Edition in the first place. So if you’ve already taken that step, with the goal of maximum gaming performance, these modifications aren’t that far-fetched as additional investments on-top of that.   

Ultimately, of course, each enthusiast must decide for themselves how much time and resources to invest and how far to push the quest for maximum performance. Such a modification is by no means a must-have for everyone, but it is an interesting feasibility study, and the changed and more efficient behavior in idle mode also revealed an unexpected consequence.

For me as a gamer and hardware tinkerer, who always enjoys squeezing the absolute maximum possible performance out of his system, the shunt mod has been an appealing topic ever since the launch of the Ampere graphics cards. And for you as a community, hopefully it was an interesting look into the electrical engineering behind the boost magic of modern hardware and a little entertainment to boot. 

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