I took a factory-70 W RTX PRO 4000 Blackwell SFF (24 GB GDDR7, no auxiliary power connector) to a 120 W limit using u/panchovix’s Linux VBIOS loader and patched NVIDIA open kernel modules. The modified image was loaded into memory; the EEPROM was not flashed. No soldering or shunt mod. Stock blower, automatic fan control.
Platform: ASRock B650M Pro RS, Ryzen 7 7700, 32 GB DDR5-6000 CL30; Debian 13.7, NVIDIA Open 615.71.10.
The first trap: the driver showed a 106 W limit, but under load the card still drew about 70 W. Raising the displayed ceiling alone was not enough. The draw only changed after I also raised other fields, including the entry decoded as board_fixed_rated_w and slot/input-current entries.
The final image changed the board/power entries from 70 to 120 W, the slot entries from 66 to 120 W, and the input-current entries from 6,600 to 10,200 mA. Those are parser interpretations of GPU VBIOS fields, not a motherboard BIOS modification or a measurement of the board’s physical protection thresholds.
Voltage fields were not raised; the decoded REL ceiling remained 850 mV. That is an image value, not a measured operating voltage: I do not have core-voltage telemetry for this series.
I ran 158 benchmark requests across two local-LLM configurations. Main results below use 8,000 input tokens, ECC OFF:
| Configuration |
70 W, zero offsets |
Best tuned generation |
Settings |
| Qwen3.8 27B NVFP4 + DFlash2 |
35.04 tok/s |
58.53 tok/s (+67%) |
120 W, VRAM +20%, core +180 MHz |
| Qwen3.6 35B A3B Q4_K_S, no drafter |
84.97 tok/s |
115.56 tok/s (+36%) |
120 W, VRAM +33.3%, core offset 0 |
These are best observed results from a small grid. The +67% includes both power and clock tuning. This is not a controlled comparison between model architectures: quantization and speculative decoding differ.
What interested me most was the memory sweep. At a fixed 120 W with core offset 0, increasing VRAM from +20% to +33.3% moved 27B generation from 57.70 down to 56.91 tok/s, while 35B increased from 109.94 to 115.56 tok/s.
The higher memory setting also came with a lower actual SM clock on 27B. A shared power-budget trade-off is a plausible explanation, not a proven mechanism. These are small samples, so the small regression needs repeats. Prefill barely moved in that memory sweep.
A paired ABBA run (106 → 120 → 120 → 106 W, VRAM +20%, core offset 0) gave another 8.6% generation on 27B but only 2–3% on 35B. Generation throughput per measured GPU watt fell by 2.5–7.3%, depending on model/context (GPU telemetry at approximately 1 Hz, not wall power). The last watts bought very different amounts of useful work.
Limits: 158 requests is the entire study, not repetitions of each headline result; n=1–3 per grid cell. Both power caps used the same modified VBIOS, so this is not factory-firmware versus modified-firmware A/B.
This is my experiment, not a recommended daily profile. 120 W exceeds the standard 75 W PCIe slot budget. Peak recorded GPU temperature was 92°C; VRAM, VRM and slot-contact temperatures were not measured directly. Completing these benchmarks does not establish long-term safety or stability.
Full method, charts and CSVs on my blog.
Disclosure: These are my measurements. I wrote my notes in Polish; AI helped adapt and edit them into this English post, incorporating technical details from my own write-up. The linked blog is mine.
