DH Motoring

Regular price $615.00

Shipping calculated at checkout.

Customer Reviews

Based on 27 reviews
186 All Inclusive BBK

Can’t beat it for the price. Plenty of low end power to make city riding fun and enough top end to keep up with traffic. Love this kit, and David made it super easy to install.

It’s worth it!!

I will be buying a second kit for our other grom. The power is incredible for this little thing. It is the most put together kit on the market. Do yourself a favor and don’t buy else here and have problems.

186 kit is a Torque Monster

SF Grom.....Very easy install. The kit came with all parts needed. Night and day difference. Turned this grom into a very fun ride. I know need a kit for my OG

Great customer service

I wasn't sure which engine modification path I wanted to take with my 2020 Honda Monkey and right from the beginning David was helpful in answering all my questions and ultimately I settled on this kit. The kit itself is brilliant, nice easy power, the tune feels good I'm very happy. The only negative would be if on the compression stroke the starter motor can struggle to turn over the bike, now this is common for all big bore upgrades and not specific to this kit, just be aware (is easily fixed by rolling the bike backwards off the compression stroke). I can attest that David offers great pre-sales and after sales support, he will see you right. I'll be back for more DHM goodies in the future!

Best bang for your buck

Good price and easy to install alot more power would recommend getting a better starter.
I'm 330 lbs and it will do 60+ no problem

**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.