GY6 Stage 2 Engine Package - 172cc - Fuel Injection

Want to save some cash with a PWK carb instead? ➡️ CLICK HERE ⬅️

Stage 2 builds on our proven Stage 1 package and adds an electronic fuel injection option for riders who want maximum throttle response, no tuning (it's 100% auto-tune), and real-world power you can feel.

This is a true drop-in for all QMJ157 engines—the largest big-bore you can run before case mods. With proper CVT and exhaust, expect around ~13 HP (nearly double stock ~7 HP) with crisp fueling across the rev range.

Reliability first: Among GY6 big-bore options, the 172 cc setup is king for durability. It stays cool without an oil cooler and takes abuse. You’re upgrading away from low-grade stock components to higher-quality parts—so you gain performance and reliability.

ProBld Full Auto-Tune EFI (Stage 2 Upgrade)

Ditch jetting forever. Our ProBld full auto-tune EFI continuously adjusts fueling for temperature, altitude, and load using built-in sensors—so cold starts, mountain rides, and weather swings feel seamless. Just key on and ride.

Why EFI over a carb? No jets to swap, no needle guessing, and no re-tunes after weather or elevation changes. EFI also manages ignition—replacing your CDI and coil for a cleaner, smarter setup.

What’s in the EFI module:

• Throttle body with integrated ECU and fuel injector (pre-installed)
• Atmospheric pressure sensor, throttle position sensor, and narrow-band O₂ sensor with weld-in bung
• Full CNC ProBld EFI intake manifold (anodized) with Viton O-ring and hardware
• High-pressure fuel pump (≈42 psi) with clamp, high-pressure feed and low-pressure return lines
• EFI wiring harness (easy 3-wire install)
• EFI magneto matched to your stator (select 11/12-pole or 18-pole)
• UNI pod air filter (pre-installed)
• Return fuel solution: Drill-in tank nipple (included) or optional EFI gas cap ➡️CLICK HERE⬅️
• EFI ignition coil (CDI function built into ECU)

We also recommend the titanium fuel pump coil mount ➡️CLICK HERE⬅️

Requirements: GY6 QMJ157 engine (150cc or 171/172cc) and an 11, 12, or 18-pole stator (8-pole not supported). Return fuel line to tank required (cap or nipple method).

Already running Stage 1? Stage 2 (EFI) is the plug-and-play fueling + ignition upgrade that unlocks the full potential of your build with zero jetting.

ProBld – Forged Piston Kit (Recommended)

For the strongest, most dialed setup, choose ProBld. The 4032 forged piston gives you forged strength with cast-level reliability for daily riding—built to pull hard and last.

• Pre-measured & installed rings: Precision-gapped and installed—just slide the piston, insert the wrist pin, and go.
• ProBld Big-Valve Head (28 mm / 23 mm): Includes all hardware others skip: intake & exhaust studs, gaskets, nuts, velocity stack, and an NGK plug.
• 5-Axis CNC clocking flange: Port-matched to 27.5 mm for seamless flow; allows full throttle-body alignment for perfect fitment.
• ProBld performance camshaft: Tuned for low-to-mid range power. With the included thin base gasket, you get a broad torque curve that keeps pulling up top.

Why ProBld? It’s what we run ourselves—maximum performance, easier install, and long-term durability.

NCY – Cast Piston Kit (Budget Alternative)

Want to keep costs down without going stock? NCY is a solid daily setup with a cast piston—reliable for commuting, though not as abuse-ready as forged.

• Rings not pre-installed: Unlike ProBld, you’ll need to install and gap the rings yourself.
• NCY Big-Valve Head (28 mm / 23 mm): Ships bare from the factory—we include exhaust studs, exhaust gasket, clocking flange, and an NGK plug so you’re not hunting parts.
• NCY camshaft: Focused on low-end torque. Pair with a gear-up kit to stretch top-end speed while keeping the grunt.

Choose NCY for a value-minded build, or step up to ProBld for the strongest, longest-lasting combo.

We’ve done the testing and trial-and-error so you don’t have to—no guesswork, no wasted time. Pick your kit, choose EFI, bolt it on, and feel the difference every time you twist the throttle.

Your move: Build the scooter it was meant to be—and make it yours.

What’s Included

• 172 cc Cylinder Kit (Cylinder, Piston, Rings, Wrist Pin, Clips, Base Gasket, Head Gasket)
• Big-Valve Performance Head (28 mm Intake / 23 mm Exhaust)
• Performance Camshaft (ProBld or NCY depending on kit)
• 5-Axis CNC Clocking / Leveling Flange
• NGK Spark Plug
• All Mounting Hardware (Intake & Exhaust Studs, Gaskets, Nuts)
• ProBld Full Auto-Tune EFI System (throttle body + ECU, injector, EFI intake manifold with Viton O-ring, UNI pod filter, O₂ sensor + bung, EFI magneto, EFI ignition coil)
• High-Pressure Fuel Pump (≈42 psi) with clamp, feed & return lines
• EFI Wiring Harness (3-wire install)
• Return Fuel Solution (Drill-in tank nipple)

Everything you need for a reliable, high-performance GY6 build—no jetting, no missing parts.

Important Fitment Notice

Verify you have a QMJ157 engine before purchasing. If you don’t have this engine, this kit will not fit. Click here to decode your engine.

EFI requirement: 11, 12, or 18-pole stator (8-pole not supported).

Attention Buggy / Go-Kart Owners: We have not tested every GY6 QMJ157 engine variation found in buggies and go-karts. Purchase at your own risk. Most buggy owners first buy this inexpensive test kit to confirm correct stud spacing and that no case boring is required: GY6 61 mm Test Gasket Kit.