DH Motoring

Regular price $615.00

Shipping calculated at checkout.

Customer Reviews

Based on 6 reviews
Easy Install

It's the middle of Winter so I can't review the performance aspect. The install was made really easy since the piston rings are already installed the the piston is put into the cylinder for you. I would consider myself an intermediate level mechanic and I had no trouble. It's definitely a kit you can do yourself. So far I'm super happy with it. The fact that DHM flashes your ECU and you don't need to spend several hundred dollars on a Power Commander is a massive plus.

Best Complete Kit On the Market!

Super complete kit, comes with everything needed and is totally worth it! This is what the Grom should of came with from the factory!

DH Motoring has my heart <3

This kit was super simple if it’s your first time or even if you have some experience with something like this I’d watch a few different tutorials just to get multiple opinions and views of other people doing it and get a better idea of what needs to be done in what order etc just don’t be too rough and it’ll go smoothly but warning you might need a better battery over the stock one I do have a few gauges after market lights etc but that’s a way bigger piston to turn over than your stock battery is use to sending volts for your starter overall 10/10 David is a great guy really was informative and helpful through any of my questions and the buying process... :) oh p.s. if anyone is curious about speed I have just the kit stock sprockets etc with a full cage and 12 bar, I live in Florida I’m seeeing so far not done with breakin because I work a lot don’t have time for the miles but I’m getting 67mph flats with a hard wind, after breakin I expect to maybe beat that by a mph or so the torque is so much fun you can just gas up a wheelie in 1st with out having to pull.

Best bang for the buck

Ive ordered and installed 8 186cc kits. Big improvement over stock. A must have for a Grom. My personal bike has over 3k miles on this kit so far within less than a year.

Sweet kit

Put this kit on and the bike is a lot more fun. My grom is purely a stunt toy and now it clutches up so easy. I’d say it’s a go if your looking for easy bolt on torque and power

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

**Models with ABS can only be used with non-ABS ecu cores at the moment. You will get an ABS light and ABS will not function but the engine will run just fine. 

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.