Upgrading a 50cc scooter with a big bore kit can unlock higher RPM, more torque, and greater top speeds. This article presents five suitable big bore kits designed to fit GY6 engines commonly found in 50cc to 100cc scooters, ATVs, and go-karts. Each option focuses on valve size, bore diameter, and compatibility to help you choose a kit that balances performance with reliable operation. Read on for objective comparisons and guidance to select the right kit for your riding needs.
| Product | Brand | Key Benefit | Suitable Engine |
|---|---|---|---|
| KYMLAA 100cc Big Bore Kit | KYMLAA | 69mm valve length; simple installation; RPM boost | GY6 50cc/60cc/80cc |
| Glixal 100cc Big Bore Kit | Glixal | Large 18.5/20.5mm valves; higher power | GY6 139QMB/139QMA/147QMD |
| TRKIMAL 100cc Big Bore Kit | TRKIMAL | 64mm valve length; easy installation | GY6 50cc/60cc/80cc |
| Glixal ATMT1-011 100cc Kit | Glixal | Specifically for 139QMB/139QMA engines | GY6 139QMB/139QMA |
| Maoyubelt 47mm Big Bore Kit | Maoyubelt | Complete kit with rings and gaskets | GY6 50cc to 80cc |
KYMLAA 100cc Big Bore Kit for GY6
This big cylinder kit is designed to upgrade a gy6 50cc, 60cc, or 80cc engine to 100cc without EGR, enabling higher RPM, more horsepower, and faster top speed. It features a 69mm valve length version for improved airflow and performance gains. Installation is described as straightforward, making it suitable for riders seeking a relatively simple upgrade path while maintaining reliability.
Glixal 100cc Big Bore Kit with Large Valve Head
This kit emphasizes power through a large valve cylinder head assembly (18.5mm/20.5mm). It fits 69mm long valve style heads and is compatible with 139QMB/139QMA/147QMD engines. If your original head uses 64mm valves, it may require rocker arm changes to align with the kit. The design targets higher combustion efficiency and stronger mid-range acceleration, contributing to better overall performance in scooters and ATVs.
TRKIMAL 100cc GY6 Big Bore Kit
TRKIMAL’s kit is designed to upgrade to 100cc with a 64mm valve length version. The package promises easier installation and enhanced RPM capability for 50cc, 60cc, and 80cc Gy6 engines. This option suits riders who want a balance between cost, ease of assembly, and noticeable performance gains, particularly in urban and light highway riding scenarios.
Glixal ATMT1-011 100cc Big Bore Kit
Geared toward 139QMB and 139QMA engines, this kit emphasizes compatibility and reliability. It uses a 50mm inner diameter cylinder and a 13mm piston pin diameter, making it a straightforward upgrade for specific Gy6 configurations. This option is well-suited for riders who need a dependable big bore kit that aligns with common GY6 engine specs.
Maoyubelt 47mm Big Bore Kit
Maoyubelt’s kit features a 47mm bore with a complete assembly including cylinder block, piston, rings, circlips, piston pin, head gasket, and valve oil seals. The kit lists a diameter range (53.2mm) and positions itself as a size-change option to boost engine power. This option is designed for riders wanting a comprehensive package to refresh worn components while increasing displacement.
Buying Guide: Key Considerations For Big Bore Kits
- Engine compatibility: Verify bore diameter, valve size, and the specific Gy6 engine code (e.g., 139QMB, 139QMA, 147QMD) to ensure a proper fit.
- Valve size and flow: Larger valves can improve high-RPM flow, but may require rocker arms or head modifications. Confirm if additional parts are needed for your head type.
- Installation complexity: Some kits are designed for “drop-in” installs, while others may need head work, timing adjustments, or carburetor tuning.
- Performance vs reliability: Higher displacement often increases fuel consumption and heat. Consider cooling, fuel delivery, and ignition compatibility to maintain reliability.
- Supporting components: Assess whether you need a new CDI, clutch kit, head gasket, rings, or harmoniс balance upgrades to support the larger bore.
- Quality and warranty: Select kits from reputable brands and review warranty terms to protect against manufacturing defects.
- Legal and safety considerations: Ensure upgrades comply with local regulations and do not compromise braking or emissions systems.
When planning a big bore upgrade, assemble a complete parts list, verify engine model compatibility, and consider a professional tune if you are not experienced with performance modifications. A careful approach helps maximize power gains while preserving engine longevity and safety on public roads.