Honda Grom Modifications 2026: Best Upgrades, Costs & What to Know

What Are Honda Grom Engine Modifications?

Engine modifications for the Honda Grom aim to increase horsepower, torque, and throttle response from the stock 124cc engine. The stock Grom produces approximately 9.7 horsepower at the rear wheel (Dynojet data, 2026). Typical mods include exhaust systems, intake upgrades, and ECU flashing or piggyback tuners. A well-executed combination can raise output to 13–15 hp.

Exhaust Systems

Replacing the stock muffler is the most common first mod. The stock exhaust is heavy and restrictive, weighing roughly 8 pounds. Aftermarket options like the Yoshimura RS-9 ($399), Two Brothers Racing S1R ($349), and FMF Q4 ($329) save 3–5 pounds and produce a deeper, more aggressive tone without being deafening. Expect a 1–2 hp gain with a proper ECU tune.

Full exhaust systems (header + muffler) like the M4 GP Full System ($489) offer higher gains but increase installation complexity. Note that some exhausts exceed 96 dB at idle, check local noise ordinances.

Intake Upgrades

A high-flow air filter like the K&N SU-5588 ($49) or DNA Performance ($62) allows the engine to breathe better. Pairing an intake with an exhaust and ECU tune is the most effective sequence; a standalone intake without tuning can actually reduce performance by leaning out the air-fuel mixture.

ECU Tuning & Flashing

The stock ECU runs a conservative fuel map. Reflashing it, via services like DHM (David's House of Motorcycles) or Powervision 3 ($399), optimizes fuel and ignition timing for aftermarket parts. A flash alone can add 1–2 hp on a stock engine. DIY flashing is possible with Nelson Racing Engines Grom ECU Flash Tool ($179) but requires some technical comfort.

Stock Honda Grom suspension is adequate for city commuting but soft for spirited riding. The front fork uses 31mm non-adjustable tubes; the rear has a single shock with preload adjustability only. Upgrading suspension transforms stability, cornering confidence, and braking performance.

Front Fork Upgrades

The most cost-effective front-end improvement is replacing the fork oil and springs. Race Tech Gold Valve Cartridge Emulators ($219) paired with Race Tech .65 kg/mm springs ($95) improve compression and rebound damping dramatically. For a pre-built solution, Ohlins 650-1472 ($1,099) cartridges offer full adjustability but require professional installation. Many Grom owners report a 30% improvement in front-end feedback with a basic spring/oil swap (common forum consensus, 2025–2026).

Rear Shock Upgrade

The stock rear shock sags under load and lacks rebound damping. The most popular upgrade is the Ohlins HO705 ($599), a fully adjustable shock with spring preload, compression, and rebound. Bitubo WME ($489) offers similar performance at a lower price. A quality rear shock improves rear-plant and reduces pogo-ing over bumps.

Stabilizer Bars

A fork brace or stabilizer bar like the GPRO Fork Brace ($89) reduces flex during heavy braking. Combined with upgraded suspension, the Grom feels planted through corners at highway speeds (55–65 mph).

Tires & Brakes

Stock IRC tires offer adequate grip for commuting but limit lean angle and wet-weather confidence. Upgrading to Michelin Pilot Street Radial (front $79, rear $89) or Bridgestone Battlax BT45 ($110 each) improves traction noticeably. For brakes, stainless steel braided lines like Galfer Grom 3-Line Kit ($89) provide stronger, more progressive lever feel over the stock rubber lines.

Cosmetic mods are the most visible way to personalize a Grom. They range from simple decals to full fairing kits. Comfort upgrades, seats, handlebars, and mirrors, affect how the bike feels on longer rides.

Seats

The stock seat foam is thin and firm. Corbin Gunfighter ($375) offers contour molding and firmer foam that reduces fatigue on rides over two hours. Djorna Windscreen ($89) reduces wind pressure on the chest at highway speeds, making longer trips more comfortable.

Handlebars & Controls

ProTaper Mini High bars ($79) improve ergonomics for taller riders by raising the grip position 1.5 inches. ASV C5 Grom Levers ($119) provide adjustable reach, smoother action, and a more positive feel at the lever. Install requires drilling new handlebar holes or buying a new top triple clamp (e.g., Barker's Grom Top Clamp, $99).

Bodywork & Lighting

Full fairing kits like Tyga Style ABS Fairing Set ($399) transform the Grom’s appearance in the style of a miniature sportbike. LED headlight upgrades, O'Fluorescent M-Stroke Headlight ($149), vastly improve nighttime visibility. Integrated rear taillights (e.g., MotoMinded Grom Integrated Taillight, $119) clean up the tail and add sequential turn signals. Expect installation time of 2–4 hours for full fairings, and 30 minutes for the headlight.

The most common Grom modding mistake is stacking parts, adding an exhaust, intake, and cam without a proper ECU tune. Without tuning, the engine runs lean, risking detonation and overheating. Another frequent error is cheaping out on suspension. A $200 exhaust may sound good, but a $300 shock upgrade will improve the ride far more. Avoid budget-tier Chinese exhausts, they often blow out packing within 2,000 miles and can fail noise tests.

Budget Considerations

A realistic budget for a well-rounded, street-focused Grom build is $1,000–$1,500:

• Exhaust + intake + ECU flash: ~$700
• Rear shock upgrade: ~$500
• Tires (set): ~$180
• Braided brake lines: ~$90

For a full track/performance build with suspension cartridges, big-bore kit (e.g., 181cc from BBR, $899), and cam (e.g., DHM Stage 3 Cam, $219), budget at least $4,000 including labor.

Warranty consideration: Extensive modifications may void certain aspects of Honda's factory warranty. Keep stock parts to swap back if needed.

Expert Tips

• Install an ECU tune before or simultaneously with an intake/exhaust upgrade to avoid a lean condition.
• Buy a shock that matches your weight, springs are available for specific rider weight ranges.
• Check local noise laws before installing a straight-through exhaust; many tracks enforce 96 dB limits.
• Keep stock parts in a bin, they retain re-sale value for new owners and allow easy reversals.
• Torque all bolts to spec (Grom service manual) to avoid stripped threads on aluminum parts.

Mistakes to Avoid

• Adding performance parts without a tune, lean mixture can damage the engine.
• Buying a cheap, unbranded exhaust, poor build quality, high noise, short lifespan.
• Ignoring suspension when adding power, a 13 hp Grom with stock suspension understeers badly.
• Assuming all aftermarket parts fit all model years, check compatibility with your 2013–2020 or 2020+ model.

Pros and Cons

👍 Pros: Lightweight and easy to work on; massive aftermarket support; mechanical work is straightforward and rewarding; low cost per mod; excellent resale value for well-documented builds.

👎 Cons: Small displacement limits speed even after mods; tuning can be tedious without a professional; some parts (big-bore kits) require engine disassembly; noise restrictions may limit exhaust choices.

Bottom Line

Honda Grom modifications are a practical and fun way to personalize performance and looks. For most riders, the best investments are a quality exhaust, ECU tune, and a rear shock upgrade. Avoid cheap parts and always tune when changing air-fuel ratios. A well-thought-out build significantly improves the Grom experience without breaking the bank.