DH Motoring

Regular price $645.00

Shipping calculated at checkout.

Customer Reviews

Based on 62 reviews
Feels like a new bike

Very impressed with this kit! I opted for the reflash as well as the stock intake with the koso tube. The tune is spot on and the grom feels like an entire new bike. Power wheelies like nothing in 1st and second gear. Had a few questions and dave was quick to respond via email. Only thing i would suggest, get longer oil cooler lines if you plan on mounting the oil cooler a bit higher up like I did. Thanks DHM super happy with the kit so far (150 miles of ice racing so far on kit)

Jay Lineberry
Hell yeah

The best kit you can buy hands down and knock out installing in an afternoon. Took it for a ride that morning before install, topped out at 62. Installed kit and rode that night topped out at 71. She’s a ripper now!!!

Jukka Kukkonen
Monkey power

Monkey with bbk 186 kit is powerful and good to drive on highway.I have a 16-t front sprocket and I changed a little colder spark plug than genuine spark plug is.I have driven about 500km.
Thanks David !

Daniel J. Sandberg
Great kit, but starter needs an upgrade too

Love the kit! Installed easy, extra torque is awesome! But the stock starter is barely enough to start it up, what starter is recommended?

Steven M
186 bbk

Great kit. Easy to install. Would prefer if it came with a option to mount the cooler up high instead. Dhm was super quick to ship and easy to get a hold of and answer any questions. Thing starts up and sounds like a completely different bike. Still breaking it in but definitely a good easy bolt on kit would recommend to anyone that wants that extra torque

**Kits are now shipping within 2 weeks from order date!**

We are proud to introduce the first "all inclusive" big bore package for the Honda Grom!

The DHM 186 kit includes everything you need to convert your Honda Grom in to a big bore machine. You no longer have to piece parts together with expensive components to get more power out of your bike. Our kit utilizes hardware from TBParts along with an OEM Honda injector and our software tuning to create a reliable and powerful kit that makes the Grom easier and more fun to ride. 


  • 186cc Cylinder and Piston
  • Complete Oil Cooler Kit
  • OEM Honda PCX150 Fuel Injector
  • DHM Reflash
  • TB Camshaft (you can select an option to reduce the price if you already own one)

Performance Data:
  • 16.5 HP and 14.5 Ft/lbs of torque! A gain of 74% in HP and 67% in torque over a stock bike. (Dyno chart available in photos above)
  • 20-50mph in 5 seconds compared to a stock bike at 9 seconds


TB Camshaft. This kit is designed to be run with the TB camshaft. If you already have one, you do not need to select it. If you do not already own one, please add it by using the drop down menu when ordering.

TB Clutch Kit. If your stock clutch is worn, or you'd just like a harder bite, we offer the TB clutch kit as a $40 upgrade.

How the Reflash works: 

You will need to send us your ECU to be reflashed for proper fueling to run with the kit. If you do not wish to send us your ECU, we can provide a core ECU for an additional fee. Please select your ECU option from the drop down menu when ordering. You can receive a refund of $75 when returning your ecu if you order a core when checking out.

Since our primary business is building race engines, we take a lot of pride and care in our engine assembly. Before shipping, we will check all ring gaps, and we will also align the rings in the piston and install the piston in to the cylinder for you with the alignment we recommend! 

**An upgraded intake and exhaust are not required but are highly recommended!

Completely upgradeable:

Since we are flashing the OEM ecu, you can still use piggybacks on top of this kit should you decide to make any changes. If you would like to add a big valve head or change the cam, etc., you can do so and use your piggyback fuel controller (pcv, etc) to tune it as you normally would. The fact that we've reflashed the stock ecu for fuel and timing will actually provide a better base than the stock, unmodified ecu! 

***Requirements and General Information:

The ECU reflash requires your stock narrowband O2 sensor to be installed and plugged in. If you have removed this to use another fuel controller, you will need to reinstall it. The ecu will learn and adapt over the first 15-20 miles, so acceleration and overall ride ability will increase up to that point. 

Installation instructions are not included. If you are not capable of working on these engines, having a shop perform the install is recommended.

This kit is designed to be bolt-on, reliable power. However, at the end of the day the Grom engine is a very simple air-cooled engine, and heat is the enemy. If you plan on taking regular highway trips, an oil temperature gauge is highly recommended to make sure the engine does not overheat. OPMID and Koso both offer great options.