Every upgrade we supply and fit exists because it solves a real problem we’ve seen on real cars, not because it looks good on a parts list. A factory M3W is already a brilliant thing. These are the upgrades that make it noticeably better, in the order we’d actually recommend doing them if you’re working through a list rather than a wish.
1. Fuel Pump Reliability Upgrade
Every M3W leaves the factory with a Chinese-made fuel pump which is prone to unexpected failure. We remove the original pump from the housing and replace it with a USA-made Walbro unit, renowned for its reliability. It’s a straightforward change that removes one of the few faults on this car capable of stopping you at the roadside with no warning at all, which we cover in more detail in our reliability guide.
2. Regulator Rectifier Reliability Upgrade
Again, a common failure point of the factory-fitted equipment. We prefer to upgrade the standard unit to a Harley-Davidson branded device that delivers robustness and consistent performance. On a car running only a lawnmower-sized battery, a charging system you can rely on matters more than it would on a conventional road car.
3. Centa Drive Conversion
If you have a 2012 to 2014 car fitted with a Harley Cush Drive, it is essential to change to a Centa Drive to avoid damage to the crankshaft. Once a Centa Drive is fitted, we recommend fitting the ‘easy roller change’ upgrade, which involves changing the inner core of the Centa Drive and cutting an access hole in the bell housing. This enables you to change the rollers as a maintenance routine without having to remove the engine.
4. Engine Mount Kit
The thumping V-twin gives the M3W its unique character. It does however put great strain on the chassis frame and can cause cracks and failure. Our engine mount kit upgrades the fixings between engine and chassis, reducing vibration and delivering a smoother ride. You can even see out of the rear-view mirrors.
5. Suspension Upgrade
The factory suspension setup is a sensible compromise for a production car built to a price, which is another way of saying it leaves real performance on the table. We supply and fit Öhlins units for owners who want more than that: properly adjustable compression and rebound damping, tuned to how you actually drive the car rather than a single setting that must work for everyone. The difference shows up most on a B-road you know well, where the car simply follows the surface better instead of skipping over it.
Whilst you can pay your money and take your choice of damper upgrades, we strongly recommend the Öhlins setup specifically engineered for the M3W. The handling and performance are transformational, the difference between night and day.
6. Rear Sprocket
The factory rear sprocket is machined from a fairly soft aluminium, which wears quickly once road grit gets trapped against the drive belt and starts acting like grinding paste. Our lightweight steel version solves that durability problem outright, and it sharpens throttle response at the same time. Less unsprung rotating mass at the rear wheel means less energy wasted spinning the sprocket itself up and down, so more of the engine’s output actually reaches the road, and the suspension has an easier time keeping the wheel in contact with it.
7. Performance Upgrades & Weight Saving
If you want more from your M3W than the standard car delivers, then there are a host of options to increase performance and reduce weight. Here are just a few of our favourite upgrades.
Upgraded Camshafts
More power for the S&S V-twin starts here. Reworked to 569 performance specifications, these camshafts open up meaningful mid-range torque and top-end power over stock, professionally mapped for reliability rather than chasing a headline number. There’s a second, less obvious benefit too: fitting them is a practical route to removing the factory “Easy Start” decompression mechanism, a known long-term wear point we cover in our engine guide, in favour of a simpler, more robust standard cam profile that doesn’t rely on a small centrifugal pin staying in perfect working order for years.
Performance Exhausts & Air Filters
A free-flowing exhaust and an improved air filter are key to an unleashed engine, allowing it to breathe and exhaust more freely. Given that the engine was originally designed to be fitted to a motorcycle with short pipes, once installed in the M3W with longer exhausts, performance is restricted. We offer various solutions, so talk to us about the options.
Carbon Fibre Mudguards
A popular upgrade that significantly reduces the M3W’s unsprung weight and consequently reduces bump steer. They offer a stylish design and eliminate the failure points and corrosion associated with the factory-fitted steel mudguards.
8. Disc Brake Conversion (Sold Out, Mk 2 Coming Soon)
The factory drum brake relies on a brake cylinder that was originally sourced from a 1970s Ford Transit. It corrodes, it fades under repeated hard use, and it simply isn’t what you want slowing a car with this much character down a fast B-road. Our signature conversion swaps in a modern caliper and drilled disc, which dissipates heat far more effectively under repeated braking and gives you a firmer, more progressive pedal instead of the long, soft travel the drum setup is known for.
9. 3D-Printed Cabin Accessories
The M3W’s cabin was never designed with storage in mind, and generic universal brackets never quite fit its dimensions properly anyway. Our custom-designed 3D-printed trays, phone mounts and bespoke organisers are modelled specifically for this cabin, so they solve the storage problem without drilling or permanent brackets. The cockpit stays exactly as minimalist as it should, and your phone, wallet and keys stop sliding around the footwell on a spirited drive. It’s a small upgrade compared to the others on this list, but it’s consistently one of the most appreciated once it’s fitted.
Every upgrade above is fitted by us, with proper setup, testing and documentation. Parts are only ever as good as the installation behind them, and we’d rather you judged us on that than on a spec sheet.
Budgeting the Order
If you’re working through this list gradually rather than all at once, prioritise the reliability upgrades first. They earn their place regardless of how you use the car. Once the reliability fundamentals are sorted, think about how you plan to use your M3W: Sunday pub runs, or long-distance touring? Choose performance or weight-saving enhancements to match your driving style. Cosmetics and accessories are entirely down to personal preference. Combining several upgrades into one visit also saves on labour compared with spacing them out over separate bookings, so it’s worth talking through the full list with us even if you’re only planning to commit to one or two straight away.
Upgrades FAQs
A couple of questions worth answering directly.
We’d approach it in two stages. Stage 1 is upgrading to an appropriately designed free-flowing exhaust system and changing from the stock air filter to one that delivers more air flow. Stage 2 is adding our performance camshafts, reworked to 569 specifications for the S&S V-twin and professionally mapped for meaningful mid-range torque and top-end power without compromising reliability.
UK block exemption regulations mean fitting upgrades through an independent specialist doesn’t automatically void a manufacturer warranty, provided the work is documented and carried out to the correct standard, which we do as standard on every job. For insurance, always let your insurer know about any performance modifications, since undisclosed changes can affect a claim.
