Upgrading a 50cc scooter with a big bore kit can unlock more RPM, added horsepower, and higher top speeds. This guide highlights five top options that fit 50cc to 100cc engines in the Gy6 family, focusing on reliable kits with larger valves, easier installation, and strong performance signals. Below are targeted picks with key features to consider, followed by a buying guide to compare options and ensure a solid match for your scooter’s setup.
| Product | Brand | Key Feature |
|---|---|---|
| GY6 Cylinder Rebuild Kits Kymlaa 100cc Big Bore Kit | KYMLAA | 69mm valve length, 100cc upgrade, simple installation |
| Glixal GY6 100cc Big Bore Kit with Large Valve Cylinder Head | Glixal | 18.5/20.5mm valves, large valve head for more power |
| GY6 Cylinder Rebuild Kits Trkimal 100cc Big Bore Kit | TRKIMAL | 64mm valve length, straightforward installation |
| Glixal ATMT1-011 139QMB Big Bore Kit | Glixal | 50mm cylinder bore, compatibility with 139QMB/139QMA |
| Maoyubelt 47mm Big Bore Kit | Maoyubelt | Diameter 47mm, tall power increase from 50cc to 80cc |
KYMLAA 100cc Big Bore Kit for Gy6 50cc to 100cc
This kit is designed to upgrade a Gy6 engine from 50cc or 60cc up to 100cc, without EGR, enabling higher RPM and more power. The 69mm valve length version supports improved intake and exhaust flow for better performance. It is positioned as a straightforward installation option, making it suitable for hobbyists and riders who want a noticeable boost without complex modifications.
Glixal 100cc Big Bore Kit With Large Valve Head
Glixal’s kit focuses on a large valve cylinder head assembly (18.5/20.5mm). This setup is aimed at extracting more power from 139QMB/139QMA/147QMD engines and is compatible with 69mm long valve style heads. If your current head uses smaller valves, you may need to replace rocker arms as included in the kit to maximize performance gains. The kit emphasizes improved airflow for higher horsepower output.
TRKIMAL 100cc Big Bore Kit for 64mm Valve Gy6
This big bore option is geared toward Gy6 engines with a 64mm valve length, offering a robust upgrade path from 50cc or 60cc configurations to 100cc. It emphasizes easier installation and a balance of RPM rise with practical driveability, making it a popular choice for riders who want noticeable acceleration without sacrificing reliability.
Glixal ATMT1-011 139QMB 139QMA Big Bore Kit
This kit is specifically noted for the GY6 139QMB 4-stroke engine family. It provides a 50mm inner cylinder diameter with a focus on reliable performance improvements. It’s a straightforward upgrade that aims to deliver more torque and smoother power delivery, aligning well with riders looking for a practical, drop-in enhancement to their scooter’s core engine.
Maoyubelt 47mm Big Bore Kit For Gy6
Maoyubelt’s kit increases cylinder bore to 47mm, expanding the power potential of Gy6-based scooters from 50cc up to an 80cc range. It includes a complete set with piston rings, clips, head gasket, and valve seals, providing a full upgrade package. The kit is marketed as a way to change engine size and unleash stronger performance, appealing to riders who want a relatively simple, all-included upgrade path.
Buying Guide: Key Considerations For Big Bore Upgrades
- Engine compatibility: Verify bore size, valve length, and cylinder head compatibility with your specific Gy6 model and year. Some kits target 69mm valve setups, others use 64mm or 50mm configurations. Mismatches can require additional parts or may not fit properly.
- Valve size and head design: Larger valves can improve airflow and power but may require rocker arm adjustments or head work. Consider whether your kit includes a compatible cylinder head or if extra components are needed.
- Installation complexity: Some kits are “drop-in” but others need precise timing, head machining, or ECU/ignition recalibration. Assess your mechanical skills or budget for professional installation if needed.
- Ignition and CDI: Certain kits pair with performance ignition coils or racing CDIs. Ensure compatibility with your existing ignition system and check for required wiring or mounting changes.
- Supporting components: Upgrading to a bigger bore may require upgraded studs, gaskets, pistons, rings, and seals. Review included parts and determine if you need to source additional items.
- Jetting and fuel delivery: A larger bore can alter air-fuel requirements. Be prepared to adjust carburetor jets or EFI tuning to maintain optimal combustion and drivability.
- Reliability vs. performance: Some kits prioritize maximum horsepower, potentially at the cost of power delivery smoothness or longevity. Consider the riding style and maintenance commitment you’re willing to undertake.
- Legal and warranty considerations: Big bore upgrades can impact warranty status and local emissions rules. Check local regulations and any manufacturer warranty implications before installation.
- Price and availability: Compare kit contents, included hardware, and support from the seller. A slightly higher price may reflect a more complete kit with detailed instructions and proper fitment.
- Maintenance implications: With increased displacement, regular maintenance frequency may rise. Plan for more frequent oil changes, valve clearance checks, and cooling considerations.
All five selections target the core goal: expanding displacement and improving airflow to deliver more RPM and power on a Gy6 50cc scooter platform. When choosing, align the kit’s valve size, bore diameter, and compatibility with your engine family and year. Coupled with proper installation and tuning, these kits can substantially boost performance while preserving rideability.