| Spec | GX270 | GX390 |
|---|---|---|
| Displacement | 270 cc | 389 cc |
| Bore × stroke | 77 × 58 mm | 88 × 64 mm |
| Net power | 8.4 hp (6.3 kW) @ 3,600 rpm | 11.7 hp (8.7 kW) @ 3,600 rpm |
| Net torque | 14.1 lb-ft (19.1 Nm) @ 2,500 rpm | 19.5 lb-ft (26.5 Nm) @ 2,500 rpm |
| Compression ratio | 8.5:1 | 8.2:1 |
| Oil capacity | 1.16 US qt (1.1 L) | 1.16 US qt (1.1 L) |
| Fuel tank | 5.6 US qt (5.3 L) | 6.4 US qt (6.1 L) |
| Dry weight | 55 lb (25 kg) | 69 lb (31.5 kg) |
| Ignition | Digital CDI, variable timing | Digital CDI, variable timing |
| Starting | Recoil / electric | Recoil / electric |
| Size (L × W × H, min) | 15.0 × 16.9 × 16.6 in (380 × 429 × 422 mm) | 16.0 × 19.1 × 17.7 in (407 × 485 × 449 mm) |
Source: Honda Engines official specification pages (engines.honda.com/models/model-detail/large-gx, engines.honda.com/models/model-detail/x-large-gx), checked 2 Nov 2026. Power is SAE J1349 net output measured by Honda; engines installed in equipment may vary. This site is independent and not affiliated with Honda.
What the difference means
- Torque is what you feel in a tiller, pump or go-kart pulling from low speed: 14.1 vs 19.5 lb-ft at 2,500 rpm.
- Mounting: they belong to different Honda size classes (15.0 × 16.9 × 16.6 in (380 × 429 × 422 mm) vs 16.0 × 19.1 × 17.7 in (407 × 485 × 449 mm)), so the bolt pattern and frame space differ – a swap usually needs a new mounting plate.
- Shaft: both come in several PTO shaft types (straight, tapered, threaded, reduction). The type letter after the model name on the engine label tells you which.
- Fuel use rises with load and displacement; the bigger engine only costs more fuel when you actually use its extra power.
Rule of thumb: pick the smaller engine when the equipment maker lists it as an option and you run it at part load; pick the larger one for pumps, splitters and karts that run near full load for long periods.