Feedback on a dual RTX 4090 build.


I've been using the same macbook air since 2011, and as a graduation present to myself I was going to build a nice PC to experiment with some open source LLMs and also use as a gaming machine to play some games (probably Baldurs Gate 3). I have not built a computer before so I would appreciate any feedback. 

The main difficulty is that I would like to get dual RTX 4090s to run some of the larger LLMs (LLAMA 2 70b requires about 35gb of vram). In order to fit, I was going to go with dual MSI GeForce RTX 4090 SUPRIM LIQUID Xs since they each only take up 2 PCIE widths instead of the usual 3.

A couple of notes/questions

  1. I am planning on starting with one RTX 4090 and adding the second one later. Are there any issues with under-drawing power from the PSU. With 1 gpu, I will be at 758/1600 watts according to the wattage estimator, and 1208 with the 2nd gpu added.
  2. I plan on dual booting ubuntu for LLM work and windows for gaming. I don't think this matters but just checking.
  3. Do you think it will be possible to add another 2 x 48gb of DDR5 and keep the 6400 speed?

Does this look like a reasonable build? I would greatly appreciate any thoughts or concerns y'all might have.

CPU: (1) Intel Core i9-13900K Raptor Lake 3.0GHz Twenty Four-Core LGA 1700 Boxed Processor - Heatsink Not Included ($555.98 EACH)

Motherboard: (1) MSI Z790 MPG Carbon WiFi Intel LGA 1700 ATX Motherboard ($399.99 EACH)

RAM: (1) G.Skill Trident Z5 RGB 96GB (2 x 48GB) DDR5-6400 PC5-51200 CL32 Dual Channel Desktop Memory Kit F5-6400J3239F48GX2-TZ5RK - Black ($399.99 EACH)

Case: (1) Lian Li Lancool II MESH Type C RGB Tempered Glass ATX Mid-Tower Computer Case - Black ($109.99 EACH)

Power Supply: (1) EVGA SuperNOVA 1600 P Plus 1600 Watt 80 Plus Platinum ATX Fully Modular Power Supply ($344.99 EACH)

Video Card: (2) MSI GeForce RTX 4090 SUPRIM LIQUID X 24G Hybrid Cooling 24GB GDDR6X PCIe 4.0 Graphics Card ($1,799.99 EACH)

M.2 / NVMe SSD: (2) Inland Platinum 2TB SSD NVMe PCIe Gen 3.0x4 M.2 2280 3D NAND Internal Solid State Drive, PCIe Express 3.1 and NVMe 1.3 Compatible, The Ultimate Gaming Solution ($215.99 EACH)

Heatsink: (1) Noctua NH-D15S Chromax Black CPU Cooler ($119.99 EACH)

Thermal Compound: (1) Noctua NT-H1 High-Performance TIM - 3.5g ($10.99 EACH)

thanks in advance!


  • PowerSpec_MichaelB

    Few things to touch upon here. The dual RTX 4090's for the larger LLMs should work fine. Gaming wise, you'll mostly only be using a single GPU unless you use an API that supports explicit multiadapter mode (DX12) or Linked Display Adapter (LDA) mode through WDDM. BG3 might be able to do this on Vulcan, but BG3 on Vulcan also has some crashing issues at the moment, so I'd still recommend DX11 for stability.

    On the hardware selection itself;

    • The CPU and motherboard choice looks fine. The 13900K is a solid option no matter how you slice it. If you want longer platform longevity, you might consider looking at AM5, but AM5 memory support is wonky when running 2DPC and multi-rank kits.
    • Your memory selection is worrisome. 2x48GB at 6400Mhz is going to be hard to run on most processor memory controllers without some manual tweaking. Getting 4 DIMMs to do this in a 2DPC configuration on just XMP alone is going to be nearly impossible. This means you'll likely need to do some manual voltage/timing adjustments to make 6400 work, and even then, there is no guarantee. MSI is listing 2DPC dual-rank DIMMs at 5600Mhz max:
    • The two RTX 4090's you plan to use won't do well in the Lian Li Lancool II chassis you selected. Both GPUs have a 240mm AIO and the chassis doesn't really support 240mm AIOs in a way that is conducive to having them on a GPU. If you are looking for single/dual slot 4090's in a multi-GPU configuration, you'll likely need to use a water block and go with a custom loop. I get that this is your first GPU build and that custom loops would be very daunting for a first time, I'd still recommend this route since you can add a CPU block to the loop and cool everything with a couple 360mm radiators. We offer build services to help if you would rather us perform the labor. For your specific workloads, I would actually recommend soft tubing and quick-disconnects. This makes servicing the loop and swapping in new components a very easy process without having to drain the system.
    • I'd definitely recommend sticking with the 1600W PSU if you are going dual RTX 4090's. It'll be easier on the PSU in the long run and should put you right in the best efficiency curve of the PSU when under load.

    If you want to avoid custom water loops, I would probably go with this chassis instead: It's extremely pricey, but it supports an inverted motherboard tray and has plenty of space for you to mount both radiators from the GPUs without the NH-D15 being in the way of your tubing. You can see the different configurations on Lian Li's website:

    Definitely looks like an interesting build though, wish you the best of luck with it.

  • surfsup

    Thank you so much for this! This was incredibly helpful.

    I already have the lancool II, so I'd like to not get a different case. At your suggestion, I started going down the custom cooling rabbit hole, and am going to try to build a soft tubing loop with the Asus 4090 tuf + Corsair water block for it.

    A couple of follow up questions:

    1. I'm going to try to get 360mm radiator (Hydro X Series XR7) on the front panel, 240mm on the top (Hydro X Series XR5), and 120 (Hydro X Series XR5) on the back panel with the Corsair Hydro X Series XD5 RGB Pump/Reservoir Combo. Do you think that's enough for the full 2 gpu build in the lancool II?
    2. Re: the ram, if I switch to these 5600 speed Corsair Vengeance RGB 96GB (2 x 48GB) DDR5-5600 PC5-44800 CL40 Dual Channel Desktop Memory Kit CMH96GX5M2B5600C40, is that more likely to work/be stable out of the box?

    Since this is my first build, I'm going to take advantage of the integrated graphics chip in the 13900k, setup the basic parts / cooling loop without the GPUs and then gradually add. The GPU to water block conversion is the part that on paper seems the scariest to me (although I'm sure there will be other scary moments I am not anticipating :) )

    I made a rough sketch of the plan, getting stoked about it.

    Thanks again for your help MichaelB!

  • PowerSpec_MichaelB

    If you are going the route of a custom loop, we can definitely make the Lancool II work. In fact, I'll give you a picture of a new test bench I just built in our lab for GPU testing:

    This loop is designed for us to use quick disconnect fittings to add/remove hardware quickly so we can test both waterblocked and aircooled cards with minimum downtime.

    Now to answer your questions;

    1. A single 360mm radiator + 240mm radiator might not be enough to cool both RTX 4090s unless you are comfortable undervolting them. Adding the CPU to the loop is also going to add more heat as well (roughly 300-320W under load) and unfortunately that extra 120mm radiator won't really help much there. I would either air cool the CPU and run both GPUs in a loop for this chassis, or run a single GPU in the loop and air cool the other card. Since the blocked card is single slot, you might be able to do this without an issue.
    2. 5600Mhz would be far more doable. It might still require some slight tweaking, but it should be doable. I specialize in memory overclocking so this is something I can help you with here on the forum.

    As for the loop designs provided, I like your QDC placements, they should work fine. One issue I overlooked was the PCIe configuration of your motherboard. The bottom PCIe x16 slot is only wired for PCIe 4.0, and only x4, not x16. This might present a bottleneck in PCIe bandwidth as the slot is also wired to the board chipset and not the processir:

    I can't find any details online as to whether or not the top PCIe slot supports PCIe lane bifurcation to split it into two x8 slots. This might be a challenge if you already have this board and are planning to get the most performance out of the dual 4090 configuration.

    Some additional advice on the watercooling side of things. I would probably recommend foregoing the rear 120mm radiator. QDC fittings are already going to restrict the flow rate quite a bit. This coupled with using multiple water blocks will result in loss in head pressure. Both the modern DDC and D5 pumps offer a solid flow rate, but head pressure is often difficult to maintain. Instead, you could use a 120mm DDC pump like the one in my picture above, or use a 240mm D5 pump mounted above the PSU shroud.

    Also, I know conventional wisdom states that slight positive pressure is better for a system, make sure every radiator in the loop is configured to exhaust. You do not want to dump hot intake air into the chassis, only for the second rad to pull that hot air in. Both being set to exhaust will result in better thermals, but at the cost of dust buildup in un-filtered areas of the chassis. Keep an ESD safe duster handy to clean every month or so.

    Lastly, it might be worth considering using an external radiator since you are going with QDCs. You can run a 360mm + 240mm for gaming, then connect your loop to an external radiator for when you are running intense high precision operations on the GPUs. You can cut some holes on the back of the chassis add circular rubber grommets and run soft tubing out with a valve on them so you can swap seamlessly. I loved my old MORA3 radiator and it by itself could cool both your GPUs and CPU with relative ease. The thing was massive:

    When done right, it can also look amazing too:

  • surfsup

    That picture really helped me get a sense of the scale of the tubing/fittings! Ok making a couple of tweaks based on your reply.

    • Dropping the 120mm radiator.
    • Switching out the pump/reservoir for the EKWB EK-Quantum Kinetic FLT 120 Pump/Reservoir Combo, DDC PWM.
    • Switching from the MSI Z790 MPG Carbon to MSI Z790 MEG Ace. If I am reading the manual correctly I think, when adding the second gpu the PCIe slots should run in x8 x8 mode:

    So the new configuration would like this:

    Hopefully last questions before I start ordering parts.

    • The MEG Ace motherboard is an eATX which the lancool II can fit but anything I should be worried about there?
    • Is it ok if I mount the reservoir/pump on the front panel fan like I have in the diagram. Filling the reservoir directly over the GPU like you have in your setup makes me nervous. Would mounting on the front panel restrict airflow too badly? Since the fans are going to be in exhaust mode and pulling out away from the radiator, my uninformed guess would be that it shouldn't matter too much but what do you think?
    • So I can learn, whats the reasoning behind thinking the 120mm radiator isn't worth having?
    • I am going to get a leak tester and try to build a simple cooling loop outside of the case to do some low stakes testing/build up intuitions before trying the real thing. Are there any tips/recommendations you have for a first timer?

    Those external radiators look really cool. I think I will try that when I get to adding the second gpu.

    Just to recap the final parts round-up for single gpu build:


    • MSI Z790 MEG Ace Intel LGA 1700 eATX Motherboard


    • Intel® Core™ i9-13900K Processor


    • ASUS TUF Gaming GeForce RTX 4090 OC Edition 24GB GDDR6X


    • Corsair VENGEANCE® RGB 96GB (2x48GB) DDR5 DRAM 5600MHz C40 Memory Kit


    • 2x PNY CS2130 M.2 NVMe 2TB SSD

    Power Supply

    • Corsair AX1600i 1600 Watt 80 Plus Titanium ATX Fully Modular Power Supply


    • Corsair Hydro X Series XR7 360mm Water Cooling Radiator
    • iCUE LINK QX120 RGB 120mm PWM PC Fans Starter Kit with iCUE LINK System Hub
    • Corsair Hydro X Series XR5 240mm Water Cooling Radiator
    • 2x120mm 1300 ARGB fans (stock from case)

    Water Blocks

    • Corsair Hydro X Series XC7 RGB PRO CPU Water Block (1700/1200/AM5/AM4)
    • Corsair Hydro X Series XG7 RGB 40-SERIES GPU Water Block (4090 STRIX/TUF)


    • Corsair Hydro X Series XD5 RGB Pump/Reservoir ComboEKWB EK-Quantum Kinetic FLT 120 Pump/Reservoir Combo, DDC PWM, D-RGB, Plex

  • surfsup

    Also I was able to find all the parts at my local microcenter (Brooklyn, NY) except this: Corsair Hydro X Series XG7 RGB 40-SERIES GPU Water Block (4090 STRIX/TUF) doesn't seem to be carried. Do you think they would order it for me or will I have to purchase separately?

  • PowerSpec_MichaelB

    I think the MSI MEG Ace board is an excellent option. The VRM is insanely good and the trace layout makes it exceptional for overclocking if that is something you anticipate getting into in the future. This board also supports lane bifurcation, which is why it's able to switch from x16 to x8 to accommodate both GPUs.

    To answer your questions in order;

    • The Lancool II will support E-ATX just fine. You just need to move the cable management brace inside of the chassis to allow the board to fit properly.
    • Mounting the pump/res to the front of the chassis will be just fine. Radiator fans are designed with static pressure in mind to pull air through dense fin stacks and filters. There is enough of a gap between the pump/res that it will have no problem pulling in air to exhaust.
    • When planning a custom loop using many different watercooled components, you need to factor in both the required surface area for cooling, as well as flow restriction. The more blocks and rads you add, the more head pressure you lose from the pump to complete the cycle. You lose a lot of water pressure for each bend in the loop so it's always best to try to minimize that when possible. When you have a restrictive loop, you'll notice that flow is strong at the beginning of the loop, but weaker towards the end, and you'll feel it in the heat of the tubing and fittings towards the end of the loop. To overcome this, people typically add a second pump to the loop, or run dual loops and split the cooling configuration entirely with independent pumps per loop. For your specific configuration, I don't think it's worth sacrificing additional head pressure on the DDC pump for the small gains in surface area from the 120mm rad. Finding that balance is often tricky.
    • Using a digital leak tester is a good idea and I definitely prefer to use them over the old fashion methods of covering everything with blue shop towels and hoping for no leaks, lol. Pump up to 0.5 BAR and let it sit for 20-30 minutes. If it drops down to 0.49 BAR, that's still fine. It's important to remember that air is more porous than water so while air might leak ever so slightly, water won't under the same conditions. Also, if you want the added security, you can always combine both leak test methods (air pump + paper towel barrier) to ensure nothing happens if a leak occurs. While filling, I use one hand to fill with a fill bottle, the other hand on the chassis power button, and a surge protector near my feet to quickly power the system down while filling. This allows for a very fast response time when filling to avoid running the pump dry. A dry pump will die very quickly. Also, make sure you use a proper coolant or deionized water with added corrosion inhibitors & biocides. This is going to prolong the life of your blocks and help prevent fungal growths in the water.
      • The other added benefit of using coolant/deionized water is that its electrical conductance is very low, so if a leak does occur on a component, the risk of damage is reduced. Keep in mind that as the coolant/water comes into contact with your metal blocks, it will eventually ionize over time which will change the electrical resistance and ultimately become more conductive. If a leak does occur, simply spray the affected components down with 99% isopropyl alcohol, blow them dry with an ESD safe electric duster (NO VACCUMS!) and let them sit for a few hours prior to powering on. I've walked a few customers through this process on some catastrophic leaks and have yet to see their hardware fail when following these instructions.

    As for getting that block special ordered, I don't know if that is something they can do, but you can always ask their management team. If it is in-stock at any of the other NY stores, they might be able to work something out, but I can't really guarantee this. Overall, your component selection looks fantastic and I think you'll be happy with the end result. It's always nerve racking to build a custom loop on the first time, but that feeling goes away once you get into the groove of it. I don't mind walking you through that process either, so feel free to reach out if you have any questions during the build.

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