GY6 Stage 1 Engine Package - 172cc

This kit is for riders who want real, reliable power without the research rabbit hole. Every component is tested to work together—no case boring, no surprises. It’s a true drop-in for all QMJ157 engines and the largest big-bore you can run before case mods.

When it comes to big bore kits for the GY6, nothing is more reliable than the 172cc kit. Here’s why: the engine stays cool without needing an oil cooler, and it can take a serious beating. These kits are very reliable—often even more so than the stock motor.

Normally, when performance goes up, reliability goes down—but not here. The stock GY6 engine is built with low-quality Chinese components, while this kit upgrades you to high-quality Taiwanese components. You’re not just increasing power—you’re improving the heart of your engine.

With the right supporting parts (CVT, exhaust, and a PWK carb), expect up to ~13 HP—nearly double stock (~7 HP).

ProBld – Forged Piston Kit (Recommended)

If you want the strongest, most dialed setup, choose ProBld. It features a 4032 forged piston—giving you forged strength with cast-level reliability for daily riding.

• Pre-measured & installed rings: We do the tedious work for you. Rings are precision-gapped and installed in the cylinder—just slide the piston, insert the wrist pin, and go.
• ProBld Big-Valve Head (28 mm intake / 23 mm exhaust): Purpose-built for 172cc. Comes complete with all the hardware others skip: intake & exhaust studs, nuts, gaskets, a velocity stack, and an NGK spark plug.
• 5-axis CNC leveling/clocking flange: Port-matched to 27.5 mm for perfect flow, lets you level and clock your carb in any direction—critical for big-body PWK fitment.
• ProBld performance camshaft: Tuned for low-to-mid range punch. Paired with the included thin base gasket, you get a broad curve that pulls hard up top, too.

Why ProBld? It’s the kit we run ourselves. Maximum performance, less install hassle, longer-term durability.

NCY – Cast Piston Kit (Budget-Friendly)

Looking to keep costs down without going stock? The NCY version is a solid daily setup with a cast piston—reliable for commuting, though it won’t take repeated hard abuse like a forged piston.

• Rings not pre-installed: Unlike ProBld, you’ll need to install and gap the rings yourself.
• NCY Big-Valve Head (28 mm intake / 23 mm exhaust): Good quality, but ships bare from the factory. We add the essentials—exhaust studs, exhaust gasket, clocking flange—plus an NGK plug.
• NCY camshaft: Focused on low-end torque. Pairing with a gear-up kit is recommended to stretch that powerband at higher speeds.

Ride with Confidence

You want a scooter that runs right and rips. We’ve done the testing and trial-and-error so you don’t have to—no guesswork, no wasted time. Pick your kit, bolt it on, and feel the difference every time you twist the throttle.

Your move: Choose your kit and build the bike it was meant to be.

Important Fitment Notice

It’s very important that you verify you have a QMJ157 engine before purchasing. If you don’t have this engine, this kit will not fit. Click here to learn how to decode your engine.

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: Click here for the GY6 61mm Test Gasket Kit.