Gaming laptops often prioritize thermal balance and efficiency over raw performance, but the enthusiast community continually pushes these limits. A recent report highlights a striking example: through a simple hardware tweak, one user managed to unlock massive hidden performance in an RTX 4090 Laptop GPU—approaching RTX 5090-level benchmarks.
This modification comes from Reddit user u/thatavidreadertrue, who performed a shunt mod on the GeForce RTX 4090 Laptop GPU inside an ASUS ROG Zephyrus M16 (GU604VY). The “shunt mod” works by altering the GPU’s power-sensing circuit. Normally, power is monitored through tiny resistors known as shunt resistors. By reducing their effective resistance, the GPU’s controller underestimates real power draw, effectively raising its power limit.
In this case, the user connected a 1 mΩ resistor in parallel with the existing 5 mΩ shunt, dropping the effective resistance to around 0.83 mΩ. The GPU then “believed” it was drawing only 40–45 W, when the actual power reached ~240 W. This trick allowed the GPU to sustain higher clocks—but also dramatically increased heat output and power stress.
🔥 Thermal Engineering and Power Management #
To counteract the thermal surge, the user upgraded the cooling system extensively. The factory thermal paste was replaced with Honeywell PTM 7950 (a phase-change thermal material), and the VRM pads were swapped for Upisren UX Pro Ultra to enhance heat conduction. Even with these measures, the Zephyrus M16’s compact cooling system was operating at its limits.
No temperature logs were shared, but several 3DMark benchmark results were published. Compared to the unmodified GPU, the shunt-modded version achieved an average performance gain of 35.5%, with most subtests showing 20%+ improvements. In some tests, the results nearly matched those of an RTX 5090 Laptop GPU, suggesting the RTX 4090 mobile chip still holds untapped headroom when unconstrained by power limits.
⚙️ Risks, Rewards, and Lessons Learned #
The shunt mod effectively removes the GPU’s power ceiling, enabling higher voltage and frequency states—but it also significantly increases thermal and electrical stress. Without adequate cooling or VRM reinforcement, the risk of thermal runaway is real. Moreover, such a modification voids the warranty and can cause long-term degradation of the power delivery circuitry.
This experiment highlights that the RTX 4090 Laptop GPU still possesses remarkable untapped performance when allowed more current and thermal budget. Yet manufacturers intentionally restrict this range to maintain balance between noise, heat, reliability, and longevity—critical factors in mobile systems.
For enthusiasts, the case offers a fascinating example of extreme performance tuning and underscores the delicate balance between engineering discipline and DIY ambition. For OEMs, it serves as a live stress test of design margins and product segmentation. Ultimately, this story reinforces a timeless truth in PC engineering: pushing boundaries always comes with trade-offs.