GY6 Stage 3 Engine Package - 172cc - Fuel Injection

If this kit is sold out, or you want to piece together your own, check out all the parts here 👇

• 172cc Cast Piston Cylinder - Rolling Wrench
• 172cc Forged Piston Cylinder – ProBld
• GY6 61mm Performance Big Valve Head
• GY6 Performance Camshaft – ProBld
  
• NCY Performance Cylinder
  
• NCY Performance Cylinder Head
  
• GY6 Camshaft - NCY
  
• Shorty Pro Clocking Flange
• GY6 Scooter Spark Plug (Pre-gapped)
• 8mm Exhaust Studs + Nuts
• ProBld GY6 Full Auto Tune EFI System
  
• Yoshimura RS2 - Carbon Fiber
• Yoshimura RS - Raw Aluminum
• ProBld Carbon Fiber Weave
• ProBld Stealth Carbon Fiber

Stage 3 takes our Stage 2 EFI setup and pushes things further — adding your choice of performance exhaust and a complete 172cc top-end package. You get the full intake → fuel → engine → exhaust performance path with smoother tuning, quicker throttle response, and real-world power in the ~13+ HP range.

The Details

Stage 3 is the “complete build” tier for the QMJ157 GY6. You’re combining our full Auto-Tune EFI system with a 172cc big-bore top end, upgraded valvetrain, and your choice of exhaust — all engineered to work together as a balanced system. No random mix-and-match parts, no guesswork tuning.

With a proper CVT setup and EFI fueling, most riders see around ~13+ HP — nearly double the stock ~7 HP — and you still retain daily-ride reliability without the need for an oil cooler.

🔥 ProBld Full Auto-Tune EFI System

No jetting. No headaches. EFI auto-adjusts for altitude, temp, and humidity.

• Throttle body w/ integrated ECU + injector
• Atmospheric, TPS & narrow-band O₂ sensors
• Weld-in O₂ bung included
• 5-Axis CNC ProBld intake w/ Viton o-ring
• High-pressure fuel pump + feed/return lines
• EFI harness (minimal hookups)
• EFI magneto + high-output ignition coil
• Made-in-USA UNI pod filter (pre-installed)
• Gas-cap return option or tank-nipple return (both included)

🔥 Exhaust Options (Your Choice)

Choose the system that matches your build. All are matched to EFI + 172cc airflow.

• ProBld Raw Yoshimura-Style: hand-welded, crisp stainless tone.
• Yoshimura Fatty: polished premium finish, deep sound.
• ProBld Ruckus High-Mount: aggressive tone, compact fit.
• ProBld Ruckus Low-Mount: great for stretched/slammed builds.

🔥 ProBld 172cc Forged-Piston Kit (Best Performance)

For the strongest and longest-lasting setup:

• 4032 forged piston (superior strength + heat tolerance)
• Big-valve head (28 mm / 23 mm)
• Rings pre-installed + pre-measured
• ProBld 5-Axis CNC clocking flange
• ProBld cam — strong low-mid torque

💰 NCY 172cc Cast-Piston Kit (Budget Option)

Solid and reliable for everyday riding:

• Cast piston (you install the rings)
• NCY big-valve head
• Clocking flange + NGK plug
• NCY cam focused on smooth bottom-end torque

Want the value build? Go NCY. Want max power + long-term reliability? Go ProBld.

Important Things to Note

• Must be a QMJ157 engine — nothing else will fit.
• Buggy/go-kart GY6 variants can differ — some may require case boring or have different stud spacing.
• If you’re unsure about top-end fitment: Click here for the 61mm Test Gasket Kit
• EFI requires a return fuel line — use the included tank nipple or EFI gas-cap.
• 8-pole stators won’t work — must be 11, 12, or 18-pole.
• If running a stock Ruckus ECU or Rolling Wrench harness, you’ll need the fuel pump simulator.

If you’re not sure about compatibility, reach out — we can confirm everything before you buy.

What's Included

• 172cc Cylinder Kit (piston + rings installed)
• Big-valve cylinder head (28/23 mm) with hardware
• Performance camshaft (ProBld or NCY)
• 5-Axis CNC clocking / leveling flange
• NGK spark plug
• Full Auto-Tune EFI System (TB, ECU, injector, sensors)
• EFI magneto + high-output ignition coil
• EFI harness + fuel pump + lines
• Gas-cap return or tank-nipple return
• Made-in-USA UNI pod filter
• One (1) performance exhaust of your choice

Everything is designed to work together — no guessing what fits.