DHM 149cc Big Bore Kit for the 2022 Honda Grom

DH Motoring

Regular price $349.00

Shipping calculated at checkout.

Customer Reviews

Based on 18 reviews
Michael Ivory

I like this kit, I live on a mountain and stock bore was second and third gear shifting back and forth to keep power band, with BBK some hill I climb in 3&4 @ 30-40mph as stock was like 20 max. I don’t race but like as much power I can get out of this small bore bike.

Chris S
DHM 149 bbk

I don’t plan on installing the bbk until the winter but I installed the stage 2 (s1 cam, intake, exhaust, and ecu reflash) on the 23 monkey earlier this year and really like the performance boost. I’m hoping to get another decent decent boost out of the big bore kit. David has always been quick to answer questions and the service from orders has always been fast, thanks!

Kevin Russell
Good power increase over stock

22 grom, 149cc , dhm s1 cam, stock bottom end, home port and polish, 150cc injector, stock ported throttle body, 5 row oil cooler, chimera intake , Kemimoto exhaust stock gearing. The bike runs great I have almost 200 miles on it so far. Break in heat cycles have been done, oil changed twice. It will now hold 60 in 5th on flat ground no tuck with me weighing 200lbs and about 225 with all my gear on. Over all not a huge increase but noticeable. I was hoping that I could get it to cruise 5th @60 mph without being pined , hit 10k in 4th gear and just hold speed better. This kit accomplished all of that. Now to loose some weight so I can hit 70mph in 5th. 10k in 4th gear is 66mph but it’s a screaming. 5th will get close to 63-64 topped out right now with me sitting up. Just not enough power in 5th with a tall overdrive of 0.843 . 4th gear is pretty much the do it all gear on this bike. Pulls from 2000 up to 10k . I recommend this kit for most mild grom or monkey builds.

Ryan Kenny
Great product

First I need to compliment DHM on their great customer service, you have an issue or question send them a email and they reply back very fast.
The quality of parts are top tier, kit went together nicely, haven’t ridden it yet, just waiting for a couple of other things, but can’t wait.
Again can’t say enough about their customer service, You won’t be disappointed dealing with DHM!

Paul Perry
Love it

Great tq increase don’t have to rev to the moon.
For a big guy tq is important.

Thanks David

After over a year of development, our 149cc kit is ready to go!

Kit includes:

  • 55mm Forged Piston with RK Ring kit 
  • 55mm Sleeved cylinder 
  • Base and head gasket set

This kit provides a significant horsepower and torque increase across the entire rev range. Expect gains of 30% in the midrange over a bike with intake, exhaust and cam, and double the horsepower of a stock bike at 8500rpm.

Our ECU flash or an aRacer MiniX and AF2 combo will be required for proper installation.

ECU Flash located HERE

aRacer MiniX HERE and aRacer AF2 HERE

Extra crankcase vents are also recommended, using either of the following:

AvailMS Cam Cover Vent

MO Power Vented Cam Cover

Oil cooler: Kitaco x DHM Oil Cooler Kit

Install Notes:

  • Two base gaskets included. Use both copper and paper gaskets for pump fuel, use only the copper gasket if you are running race fuel.
  • Oil coolers are highly recommended. Keep an eye on oil temps.
  • An NGK CR9E spark plug must be used
  • Ring gaps must be set during install, we recommend .011" on the upper ring and .013" on the lower ring
  • 91 octane is the bare minimum, and 93 is preferred.
  • When using aRacer, download the quickburn for 149cc + S1 cam
  • Honda injector 16450-KZY-701 is the recommended injector for this kit.


Download setup sheet HERE