Geely’s 48.41% Thermal Efficiency Engine 🔥
This video examines Geely’s 1.5-liter mass-production gasoline engine, which claims a verified 48.41% thermal efficiency—beating Toyota, Nissan, BMW, Ford and others. It also powers the Guinness record holder for the most fuel-efficient mass-produced car. Toyota’s latest Dynamic Force engines reach about 41%, so Geely’s advantage is a huge 7.4%.
- Extreme undersquare design: The bore and stroke work out to roughly 70 mm and 97.4 mm (stroke-to-bore ratio 1.39:1), making it one of the most undersquare gasoline engines ever built. A tiny bore reduces blow-by and improves air-fuel mixing; the long stroke extracts more energy per combustion, favoring efficiency over high-revving power.
- Combustion tech: Geely’s “Fire Tornado” and “duckbill” intake create strong in-cylinder tumble. Add 500-bar direct injection, a diesel-like 15.5:1 compression ratio, laser-clad valve seats, and DLC coatings to cut friction.
But none of that explains the huge margin. The real secret is a deep Miller/Atkinson cycle: the intake valves close extremely late, making effective expansion much longer than compression. That boosts efficiency but makes the engine gutless without electric help.
- Main argument: The record isn’t from new combustion science. It’s from a hybrid-first design with larger electric motors and batteries. In Toyota hybrids, the engine is primary and electric motors assist. In Geely’s, the electric motor is primary and the engine assists—it can also help drive the wheels. That allows a much deeper Miller cycle, and that deeper cycle is where the extra efficiency comes from.
- Trade-offs: When the battery is depleted on a long uphill, the small engine can’t both drive the car and recharge. The result is a sudden, noticeable loss of power. Geely uses an “AI power cloud” to anticipate hills and pre-charge on flat ground.
- Why it matters: Toyota uses similar hardware—undersquare bores, high compression, laser-clad seats, DLC. The gap is not magic; it’s a different hybrid philosophy. Still, it’s a landmark for China: it shows Geely has caught up with established global automakers in engine engineering.
Final takeaway: The world’s most efficient mass-produced gasoline engine is really a win for bigger batteries, bigger electric motors, and AI-managed charging—not for combustion breakthroughs. But as proof of Chinese engineering capability, it’s significant.