Koso North America 170cc Big Bore Cylinder/Head Kit for Honda Grom

Ready to wake up your Grom? The Koso North America 170cc Big Bore Cylinder/Head Kit is the definitive displacement upgrade for Honda Grom riders who want real, measurable power gains without sacrificing reliability. Drop the stock 125cc limitations and step up to a purpose-built 170cc setup engineered for performance from the ground up.

The centerpiece is a unique four-valve cylinder head that dramatically improves airflow over the OEM two-valve design — more air in, more power out. Paired with a forged piston for superior strength and heat resistance, this kit is built to handle the demands of spirited street riding, track days, and everything in between.

Features

• 170cc displacement — significant power and torque increase over stock 125cc
• Four-valve cylinder head design for improved airflow and combustion efficiency
• Forged piston for enhanced durability and heat resistance
• Stainless steel 24mm intake valves
• Stainless steel 20mm exhaust valves
• Direct bolt-on fitment — no case splitting required
• Compatible with OG Grom, SF Grom, and 1st Gen Monkey

Fitment

• Honda Grom (OG / MSX125) — All Years
• Honda Grom (SF) — All Years
• Honda Monkey (1st Gen / 125) — All Years

SKU: MB623003 | Weight: 5 lbs