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DHM 149cc All Inclusive Big Bore Kit for the 2022-2025 Honda Grom

Crankcase Vent
ECU Flash Options

Here you'll find a comprehensive kit containing nearly everything you need to big bore your 2022-2024 Honda Grom (You'll need your own aftermarket intake and exhaust and we do have options linked below). By purchasing this comprehensive kit we make it as simple as possible to install by pre-gapping the piston rings before shipping. 


  • DHM 149cc Forged Piston and Cylinder Kit
  • DHM S1 Camshaft
  • Kitaco x DHM 5-row Oil Cooler Kit
  • High flow Honda fuel injector
  • AvailMS or MO Power Crankcase Vent Kit
  • NGK CR9E Spark Plug
  • DHM ECU Flash Service

Other Requirements:

  • Premium fuel (at least 91 octane, 93 is even better)
  • Quality synthetic oil of 10w40 weight or 20w50 for warmer climates

Base pricing requires you to mail your ECU in so we can program it. Once we receive it we'll flash it and send it back out with the kit so that it can all be installed together. You do have the option of purchasing a preflashed ECU as well for an additional $110.

If you already have your own aftermarket intake and exhaust setup, this kit is all you'll need. If you need an intake and exhaust, we do have a few options here:



Customer Reviews

Based on 2 reviews
James LeBlanc

All good from start to finish.
Comunications,quality,assembly,a breeze to install.
No need to look any further than DHM for 149 cc all inclusive BBK.

John Rodriguez Jr

I had the stage 2 setup (intake, Dhm s1 cam, and exhaust) prior to the 149cc big bore kit. And wow, I can tell a difference in the power and torque this kit provides. This is such an awesome kit. I’m very satisfied with the 149cc big bore kit.