The RTX 4090 has finally met its match

The RTX 4090 is a monster graphics card. It continues to challenge even standard-sized PC cases with its triple-slot size, as well as its thick power cable that can deliver upward of 600 watts. I wanted to fight back. I wanted to put the biggest GPU you can buy in the smallest case possible for the ultimate small form factor gaming experience, and that’s exactly what I did.

Not without plenty of issues, mind you, but I have the RTX 4090 up and running in a 10.4-liter PC case. For context, even a midtower like the Hyte Y40 is 50 liters. It took a lot of planning, plenty of tinkering, and a bit of elbow grease, but the small form factor PC I’ve always dreamed of is here. Here’s how I did it.

Meet the build

I built this PC for gaming. I have an RTX 4090 in it, of course, but also AMD’s Ryzen 7 7800X3D. That’s an important component. Fitting the GPU into a mini-ITX case isn’t hard, but doing so with a powerful CPU is. Before getting to that, though, here’s the build:

We need to start at the bottom because that’s the only reason this build is even possible. The Fractal Terra is a beautiful small form factor case, but it’s also very unique. Similar to the Lian Li A4-H20, the Terra includes a chamber for your graphics card and a chamber for the rest of your build. Separating the components like this is the only way to get everything inside a case this small, with the components attaching to both sides of an internal spine.

The spine on the Terra, however, is adjustable. You can give yourself more room for a CPU cooler or more room for GPU clearance. I almost had to max out the GPU clearance to fit the RTX 4090 in, and even then, I barely have enough room. A clip on the corner of the Terra’s side panel actually catches on the edge of the RTX 4090. I have to contort the case to get the side panel to close properly.

That’s the GPU solved, but as mentioned, the CPU plays a significant role here. There are plenty of tiny CPU coolers, but most can’t handle the Ryzen 7 7800X3D — except for the ID-Cooling IS-55, that is. With a Founder’s Edition RTX 4090 and this CPU cooler, you have just a few millimeters of clearance to get the side panels closed. It’s an extremely tight fit that left basically no room for cable management. I didn’t waste any space inside the PC. I also had to go with some low-profile PNY XLR-8 memory to get the CPU cooler to fit properly.

Although the build is together and functioning, I’d do things differently if I could go back. The Gigabyte B650i Aorus Ultra was a bad choice. It interferes with the cooler and doesn’t provide a secure fit on the CPU. I was able to flip the cooler and barely squeeze it into the Terra, but clearly this isn’t how the build is supposed to go. It looks like Asus ROG Strix B650E-i and MSI MPG B650I Edge both work without clearance issues.

The last note is the Thermalright ASF-Black bracket. You may have seen these types of anti-bending brackets for Intel’s latest CPUs. I’m not worried about bending with the Ryzen 7 7800X3D, but these types of brackets apparently can reduce temperatures by a few degrees. Given the limited space for a CPU cooler — and the fact that the bracket was about $8 — I figured it couldn’t hurt.

That’s the build put together, and it’s working just fine (I’m typing this article on it now). But the question isn’t if everything would fit. I knew it would fit. It’s how this build actually performs, particularly when it comes to heat and thermals.

Optimizing the curve

I hate a noisy gaming PC, which runs counter to the idea of having a small form factor build. By extension, I hate a hot gaming PC, which not only heats up my office (a converted garage) but also produces more fan noise. And from the start, I had a problem on my hands with this build.

The RTX 4090 was fine, but the CPU fan was loud and hot. At idle, I’d clock temperatures sometimes going above 70 degrees Celsius, and I’d occasionally top out at the thermal limit of 89 degrees in games. Noise was worse, climbing up to 50dB while idle and sometimes even reaching up to 60dB under loud. You can see how things held up under 15 minutes at idle and while playing Diablo IV below.

This was on the CPU, which is where I focused my optimizations. The RTX 4090 has been totally fine. Idle, it’ll get down to around 35 degrees, and I’ve never seen it go above 65 degrees under a full load. I really didn’t have any work to do on keeping Nvidia’s monster GPU cool.

The solution for the CPU? Undervolting. Undervolting isn’t about running a processor at a lower speed. It’s quite the opposite, in fact. The idea is to overclock your CPU but cap the frequency. By telling your CPU to run at a higher clock speed, but limiting it from reaching that clock speed, you move the whole curve of voltage up. This means your CPU will hit its normal boost clock speed at a lower voltage. If a processor can hit 5.2GHz at 1.2V, for example, you can overclock it to hit 5.4GHz at that same voltage. With this applied, you’ll hit the original 5.2GHz at a lower voltage.

That’s a technical explanation for something that is actually pretty simple to do, particularly with an AMD CPU. You can use the Curve Optimizer either within your motherboard’s BIOS or with the Ryzen Master utility to create a negative offset. It essentially makes it so that, for any given clock speed and voltage, you’re reducing the voltage by a certain amount. AMD allows you to set an offset of up to -30, but not all chips will be able to reach that level. For my Ryzen 7 7800X3D, I found that an offset of -20 was stable.

After setting the offset, the next step is to set some sort of cap, be it on clock speed, temperature, or power. The Ryzen 7 7800X3D is rated for 120W of power, but it rarely reaches that point. Even under a full Cinebench load, the processor never went over 90W, and in games, it would rarely crack 50W. There’s a whole separate discussion to have here, but I settled on a power limit of 70W. It sounds like I’m shaving 50W off of the chip, but I’m really not.

This took some trial and error, and if you plan on undervolting, you’ll have to go back and forth a bit, as well. You can see the massive difference it made under a full Cinebench load, though. I was actually above to gain some clock speed back due to the processor not thermal throttling, and while shaving 10 degrees off of my maximum temperature. For all of that, I dropped 1% of the performance, which isn’t enough worth highlighting.

Going a step further

The CPU was the biggest hurdle to overcome, but I wanted to optimize further. That started with undervolting the RTX 4090, which was less useful than I thought it would be. I ended up shaving 95 millivolts, taking the voltage from 1.05V to 0.945V targeting 2,775MHz as the boost clock speed. The RTX 4090 technically has a boost clock speed around 2,500MHz, though there’s quite a range. I found that the card I have settled at 2,775MHz under a full load.

You can see how the undervolt went in Cinebench R24’s GPU benchmark. I shaved a hair of power and temperature while keeping an almost identical score, but I wouldn’t say this is a significant change. You can see a difference in a 10-minute Cinebench run, but I haven’t noticed a meaningful difference in longer gameplay sessions. Still, this is technically better, and I’m not losing any performance, so I have the undervolt running.

From there, I focused my efforts on a proper fan curve, trying to combat the noise that I was getting out of the PC. I’m happy to have the fans ramp up under a full load, but I prefer to keep things quiet when there isn’t much strain on the PC — even if that means running at higher temperatures.

For the task, I used Fan Control. I’ve written previously about setting a proper fan curve, but just like undervolting, it’s a process of trial and error. Checking my idle temperatures after the undervolt, I tried to set the curve to keep the fan speeds low around that area, keeping them from ramping up until I transition into something more demanding. I’m still dialing in the curve for the CPU, but I’m pretty happy with where it’s at now.

After undervolting on the CPU and GPU, and setting a proper fan curve, here’s where I ended up after 15 minutes at idle and in Diablo IV: 

It’s a huge improvement. Temperatures are way down compared to where they were at previously, and noise has been significantly reduced, as well (particularly while playing games). I’m not totally satisfied with the idle temperatures, so I’ll be working to balance the noise and temperatures with the fan curve going forward. Compared to where the PC was at, though, this is a massive improvement.

Since building this PC, I haven’t stopped looking over in awe at just how much hardware you can pack in such a small box. It’s been a transition going from a standard midtower to a small form factor case, particularly with the noise and heat. But after getting my hands dirty with undervolting, I’m happy with where the PC has ended up.

I’m saving a ton of desk space without sacrificing any power, as well. This is just about the highest-end gaming PC you can build right now, but it takes up less space than a game console. I’ve never really considered myself big on small form factor PCs, but after moving the RTX 4090 into the Fractal Terra, I might’ve been converted.

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