DH Motoring

Regular price $615.00

Shipping calculated at checkout.

Customer Reviews

Based on 33 reviews
Great customer service

Very pleased with the purchase.
David communicated with me during a shipping delay due to a backordered part.
Received it today....
Let the fun begin.

Grom now has enough power to move a fat guy.

It was like riding a different motorcycle. Where I ride I would always have to downshift on hills, and now with the bbk I can pull any of the hills in 4th gear. I highly recommend this kit. For reference I weigh 300lbs. The only thing I wish is that the oil cooler kit came with a little longer oil lines.

Awesome product and service!

David is by far the best I’ve felt with when it comes to customer service! He will help with anything you need. Installed product and sounds and rides amazing.


COVID has been a hard time for anyone selling parts. David had some delays , but communicated with me and kept me in the loop. I appreciate that tremendously. He even overnighted the packed ( at his cost ) to help get the parts to me ASAP. I won’t Hesitate to work with him again

Great parts, great service

If I need anything for my grom and dhm has it I’m getting it there. David is knowable and willing to help. I over torqued the oil cooler bolts and broke one and David sent me a replacement for free. He also answered my many questions and helped me get the best set up for me. The kit is great bike feels completely different. It’s also the best deal and most complete kit I’ve seen, coupled with David’s service it’s a no brainer. If you’re on the fence, get it.

**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

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.