Raijintek Forkis DDC Ultra CPU Water Block Pump Combo, Reviewed

The easiest option for anyone who’s given up trying to fit a giant heatsink atop their CPU or rely upon their motherboard to support its weight may be to swap in a closed-loop cooler, but the world of liquid cooling offers so much more to those who are open to adding a little extra effort.  After all, why would anyone want to settle for a single 420mm-format cooler when they already own a case that supports two? Of course you’ll still need a water block…and a pump…

The Forkis DDC Ultra solves the fitment problem of mounting long graphics cards through the space needed for pump/reservoir combo such as the Antila D5 RBW ADD (try saying that five times, fast). CPU-mounted pumps have been popular ever since closed-loop coolers were introduced, and Raijintek isn’t even the first company to upsize one to match the larger capacity of open-loop components: Both Swiftech formerly had two versions of the block-mounted open-loop pump, and Alphacool is still selling its two versions.

The Forkis DDC Ultra’s Acetal top features threads for two G1/4 fittings and a six-pin header from which only four pins are used. It’s almost as if Raijintek overprovisioned it to support ARGB and then just skipped the lighting function.

A nickel-plated copper cold plate is polished almost perfectly on the bottom to mate with the CPU and has internal fins to increase contact area with liquid coolant. Since this heat exchanger is copper, you’ll probably want to use brass fittings and a copper radiator to prevent electrolytic corrosion. Those whose corrosion or sludge buildup fears are harder to address may like to add a bit of automotive antifreeze to their coolant, as those usually contain corrosion and microbial inhibitors.

The installation kit includes the water pump/CPU block combo, a four-conductor cable with two SATA power pins and two PWM fan pins, a dual-pattern Intel socket support plate for LGA 1150 through 2066, a replacement pump bracket that has AMD AM5/AM4 and AM3/AM2 spacing, a wrench for included standoffs, a putty spreader and packet of thermal compound, a set of spring screws with plastic washers, a set of AMD standoffs that screw into the motherboard’s original cooler support plate, a set of spacers for earlier AMD motherboards, a set of M3 threaded standoffs for the included Intel mainstream socket support plate, and a set of standoffs that are threaded to match the factory support plates of Intel’s 2011/2066 boards.

Per Raijintek’s latest instructions, the thinner package height of Intel’s LGA 1700 is addressed by leaving out the spacers that would go under the standoffs in LGA 1150-1200 installations. AMD installations look similar, but AMD builders don’t have to add the extra plate to the backs of their boards.

Raijintek also tells us to continue using the plastic washers that came with the spring screws, but alas we got tired of fighting to get the screws to reach the standoffs and mounted the thing without those. It seamed to be tight enough…

You may have noticed quick connectors in the above photo: Those came from the Alphacool components used in our motherboard testing platform. Since we had already began using that platform in our Core 1 Aurora review, we simply swapped out the platform’s D5 pump-equipped Eisbecher for our reservoir-only spare.

System Configuration
CPU	Intel Core i9-13900K: 24C/32T, 3.0-5.8 GHz, 36 MB L3 Cache, LGA 1700 O/C to 5.00 GHz at 1.25 V Core
Motherboard	ASRock Z690 Taichi: LGA 1700, BIOS 13.05
RAM	Patriot Viper Venom RGB 2x16GB (32GB) DDR5-6200 CL40-40-40-76
System Drive	Sabrent Rocket 4 Plus 2TB PCIe 4.0 M.2 SSD
Case	Cooler Master HAF XB, open, with EATX-mod tray
LC Components	Alphacool Eisbecher 150mm, NexXxoS UT60 X-Flow 240mm, Vardar F4-120ER

Cavitation occurs when an impeller (or propeller) spins so fast that it pulls apart the liquid, turning it into a gas. Those gas bubbles typically end up hitting the next impeller blade and making a noise that, depending on the design, sounds like anything from a rock tumbler to a buzz saw. Here’s what it sounds like as the Forkis DDC Ultra goes from off to full RPM:

Vapor bubbles reduce the effectiveness of both the pump and the heat exchanger, so it became obvious that we’d need to test the pump at multiple speeds. Unlike manually controlled pumps, the Forkis DDC Ultra’s PWM control allows us to tune it in BIOS or even let the board automatically manage its RPM based on CPU temperature. Thus, while our normal method for setting up a D5-powered open loop is to gradually turn down its control knob until the bubbles go away, we simply tested Raijintek’s DDC pump at full speed (~4600 RPM), a 60% PWM setting that eliminated noticeable cavitation (~3700 RPM), and a 40% PWM setting that brought its noise down to D5 levels (~2900 RPM).

Test Configuration
Load Software	Prime95 Version 30.8 Torture Test, Small FFTs
H/W Monitoring	HWiNFO64 v7.42-5030

All of that effort leads us to just one chart: Alphcool’s Core 1 Aurora leads by around 3° until the coolant starts getting warm, with the narrowing of results hinting that we might consider installing a larger radiator. Surprisingly, cavitation did not show increased temperatures at 100% PWM, despite all the bubbles and noise.

Raijintek Forkis DDC Ultra p/n 0R40B00265
Pros:	Cons:
Very good cooling performance Removable cable for easier service Integrated pump at supposed low cost	Limited availability, with no samples in USA
The Verdict:
Raijintek’s Forkis DDC Ultra offers the performance and installation convenience needed to win over some buyers…if only they could currently buy it.