Undervolting an Intel Core i9-13900K or 14900K on an ASUS Z790 board is the single best change most people can make to these chips. Done right, you drop package temperatures by 10-20°C, cut fan noise, and in a lot of cases gain a little multi-core performance because the CPU stops throttling. This guide walks through the loadline method (AC_LL / DC_LL) that keeps the CPU's own voltage control intact instead of locking it to a fixed Vcore.
Read This First: 13th/14th Gen Stability and Microcode
Before you tune anything, flash the latest BIOS. Intel traced the 13th/14th gen instability and degradation to elevated voltage requests at idle and light load (the "Vmin shift" problem). The fix shipped as microcode 0x12B in September 2024, later supplemented by 0x12F. Load the "Intel Default Settings" (or "Intel Baseline") profile as your starting point, confirm HWiNFO64 reports the new microcode, and only then start undervolting. Tuning a chip on old microcode is how people quietly cooked their CPUs in 2023-2024.
Phase 1: Hardware Analysis & Constraints
The 13900K and 14900K are essentially the same silicon (the 14900K is binned a touch higher and clocks ~200MHz more). Both pull serious power — 250W+ under an all-core load — and both will happily slam into their thermal limit on anything short of a strong 360mm AIO or custom loop. That is exactly why undervolting matters here: you are not chasing records, you are clawing back thermal headroom the chip is wasting.
VRM and Board Capability
Any ASUS Z790 ROG board (Maximus, Strix-E, Strix-F) has more than enough VRM for these chips. The TUF and Prime boards are also fine for undervolting since you are reducing load, not increasing it. The board is not your bottleneck — your cooler and the silicon lottery are.
Hard Limits for 13th/14th Gen i9
Tjmax (throttle point): 100°C. Treat 90°C under sustained load as your practical ceiling for a daily machine.
CPU voltage limit: the chip's internal cap is around 1.72V. Set IA VR Voltage Limit to 1700mV as a safety net, or leave it on Auto and let the CPU manage it.
Daily Vcore under load: there is no single "safe" number, but most well-tuned i9s sit around 1.13V–1.25V under an R23 multi-core load. The real risk is high idle/light-load voltage, which the microcode update and a flatter loadline both help with.
Understanding the Settings You'll Touch
People get lost here because ASUS exposes a dozen voltage-related options and most guides never explain how they interact. Here is the short version that actually matters for undervolting.
| Setting | What it does | Where we land |
|---|---|---|
| AC Loadline (AC_LL) | Sets the requested VID the CPU asks for under load. Lower = lower voltage = your main undervolt lever. | Start 0.20 mohm, tune down |
| DC Loadline (DC_LL) | Tells the CPU how to report/calculate its voltage. Should track your real VRM loadline so power readings stay honest. | ~1.02 mohm with LLC#4 |
| LLC (Load-Line Calibration) | Controls VRM droop under load. #1 = stiffest, #7 = most droop. Intel spec is roughly LLC#3. | LLC#3 or LLC#4 |
| SVID Behavior | Preset voltage personality. "Typical" or "Trained" is a sane baseline; "Best Case" can be too low for an average chip. | Typical Scenario |
| IA VR Voltage Limit | Hard cap on requested voltage. Caps frequency if a clock would need more. | Auto or 1700mV |
Why the loadline method instead of a fixed Vcore?
You can just set a manual override voltage and sync all cores, and plenty of people do. But that throws away the CPU's adaptive behavior — it runs the same voltage idle or loaded. The AC_LL/DC_LL approach keeps the stock adaptive curve and simply shifts how much voltage the chip requests, so idle voltages stay low (which is exactly what the Vmin-shift fix is about). The trade-off is that on 13th/14th gen the V/F curve behaves oddly when you combine a negative offset with OCTVB, which is why loadline tuning has become the community-preferred route.
Phase 2: The Tuning Matrix
This is the core loop. Change one thing, test, write it down, repeat. Do not skip the logging — you will lose track of what worked within an hour otherwise.
Step 1 — Baseline
- Load Intel Default Settings, enable XMP/EXPO, leave everything else stock.
- In HWiNFO64, open Settings and disable "ASUS EC support". It causes polling stalls that cost you 300-400 points in R23 (credit to Falkentyne on overclock.net for this one).
- Run Cinebench R23 for 10 minutes. Record max temp, max Vcore (die-sense), package power, and score.
Step 2 — Set the loadline foundation
Ai Overclock Tuner : XMP I / XMP II
ASUS MCE : Disabled - Enforce All Limits
SVID Behavior : Typical Scenario
Actual VRM Core LLC : Level 4
AC Loadline : 0.20 (mohm)
DC Loadline : 1.02 (mohm)
IA VR Voltage Limit : Auto (or 1700)
CPU Core Ratio : leave stock / Default SettingsBoot, run R23 again, and watch Vcore. A healthy chip lands somewhere around 1.13V–1.18V here. If it crashes or throws WHEA errors in HWiNFO64, your AC_LL is too low for this silicon — bump it up to 0.30 and retest.
Step 3 — Walk AC_LL down to find your floor
Now find the minimum stable voltage. Drop AC_LL in small steps and stress test after each:
AC_LL 0.20 -> test
AC_LL 0.19 -> test (step = 0.01 mohm)
AC_LL 0.18 -> test
...continue until R23 / y-cruncher errors or you WHEA / BSODWhen it finally breaks, step back up by 0.02 for a safety margin. That is your daily AC_LL. Lower AC_LL = lower voltage = cooler chip, but go too far and you get silent WHEA errors that corrupt nothing today and crash you next Tuesday.
Keep LLC and DC_LL matched
If you change LLC, your DC_LL should change to match the board's real loadline, otherwise HWiNFO's power and Vcore reporting drifts from reality. With LLC#4 on most ASUS Z790 boards, DC_LL around 1.02 is a good pairing. Don't chase a stiffer LLC thinking it helps undervolting — a flatter loadline actually keeps light-load voltage lower, which is what you want on these chips.
Step 4 (optional) — V/F point trimming for the last few degrees
Once the loadline undervolt is stable, advanced users can shave specific high-frequency V/F points using ASUS's OCTool / the V/F Point Offset menu. Enter negative millivolt offsets on the top one or two frequency points (for example -50mV on the 5.5GHz point), then validate. This is a fine-tuning step, not a starting point — get the loadline right first.
Phase 3: Validation Protocol
An undervolt that passes a 10-minute benchmark is not stable. It is "probably stable," which is a different thing. Use a layered approach.
| Tool | What it catches | Duration |
|---|---|---|
| Cinebench R23 (loop) | Quick all-core thermal + rough stability check | 30 min for baseline |
| y-cruncher (0x1 / VST / VT3) | Excellent at exposing undervolt instability fast | 1–2 hrs |
| OCCT (CPU + AVX2) | Heat + error checking with a built-in checker | 1 hr |
| Intel XTU stress / IXTU | Some chips only reveal instability here | 30–60 min |
| HWiNFO64 | Watch for WHEA "Bus/Interconnect" errors — the silent killer | Always running |
Baseline stable = passes 30 min R23 + 1 hr y-cruncher with zero WHEA. Daily-driver stable = add a few hours of mixed real use and an overnight y-cruncher or OCCT run with no errors. One Z790 owner on overclock.net made the point well: his rig passed every common test but still threw errors in Intel XTU, so don't treat a single pass as the finish line.
WHEA errors = not stable
If HWiNFO64 logs any WHEA errors during testing, your undervolt is too aggressive even if nothing crashed. Raise AC_LL by 0.01-0.02 and retest. WHEA corrected errors are the early warning; BSODs are the late one.
Phase 4: Logging Spreadsheet
Copy this straight into Excel or Google Sheets. Fill one row per change. This is the difference between dialing in a chip in an afternoon and flailing for a week.
| Date | BIOS Ver | P-Core Ratio | E-Core Ratio | Vcore (BIOS / AC_LL) | Vcore (Load, HWiNFO) | LLC | DC_LL | RAM (XMP) | Max Temp | Stress Test | Pass/Fail | Notes |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| x55 | x44 | AC_LL 0.20 | 4 | 1.02 | 6000C30 | R23 30m | baseline | |||||
| x55 | x44 | AC_LL 0.18 | 4 | 1.02 | 6000C30 | y-cruncher 1h | ||||||
Sources & Credits
Built on community knowledge
The loadline-based undervolting approach here draws on the long-running ASUS Maximus Z790 / Intel 13900K-14900K tuning thread on Overclock.net, particularly the work of RobertoSampaio (the guide's author) on AC_LL/DC_LL tuning and Falkentyne on loadline-to-VID behavior. We've verified the voltage and thermal guidance against Intel's current microcode and default-settings recommendations before publishing. Credit to those contributors — go read the original thread if you want to go deeper.
Keep Tuning
Undervolting is step one. If you're tuning the rest of the system, our DDR5 overclocking guide covers memory timings and voltages for this same Z790 platform, and the ASUS ROG Z790 BIOS settings guide covers the wider BIOS layout. On Team Red? See our AMD Ryzen Curve Optimizer guide.
At WebPC Designs we undervolt every Intel build we ship — it's free performance and longevity. If you'd rather have it dialed in for you, get in touch for a tuning consultation.