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Would you like a preflashed ECU?
Would you like a TB clutch kit?


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 or Decha HR 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 or Decha HR Camshaft. This kit is designed to be run with the TB or Decha HR 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 $50 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.

Customer Reviews

Based on 71 reviews
Wesley Chandler
186 bbk kit

Absolutely awesome people at dhm very helpful and very strait forward and easy kit!! My only regret was not doing it sooner! Also get the upgraded spring and lifter plate for ur clutches. U will most def need them



Curtis Wells
Power a grom should have!

This kit was 100% bolt on and very easy to install. Torque is insane I feel like this is the power a grom should have out of the box it completely changes the bike. I am very impressed with the tune on the ecu. I'm on the fence as far as going to the aracer but it runs and idles so good the only benefit would be if I were to switch to different fuels as I don't really plan on going much further with the grom. Time will tell but if you are thinking about installing a BBK just do it!

Awesome Customer Service

So Helpful and Responsive to all emails. They went out of their way to make my experience great. Will buy another for our second Grom soon

Coby Varns
Best upgrade

I’ve put maybe a little over 100 miles on this BBK kit and I have to say it’s probably the best purchase I’ve made for my grom but I would recommend getting a higher CCA battery but maybe that’s me customer service is amazing David was a great help and keeping me updated on when a new shipment would be in and answering questions I had before I committed to my purchase all in all 10/10 for product and customer support