After researching manufacturer specifications, published performance data, and aggregated owner feedback across forums and retailers, we evaluated the top exhaust options for the Honda Grom that prioritize power gains. While no bolt-on exhaust dramatically transforms the Grom’s 125cc engine, certain designs do free up measurable horsepower and torque, especially when paired with an ECU tune. Our guide compares seven real products, highlighting real limitations and who should skip each pick.
| Photo | Product | Score | Buy |
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Yoshimura RS-9T Full Exhaust System Best Overall for Power Full system; stainless steel header with carbon fiber or stainless can; 2.5 lb weight savings |
9.0 | 🛒 Check Price |
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M4 GP Carbon Fiber Slip-On Exhaust Best Slip-On for Power Slip-on; carbon fiber can; includes removable baffle; weight 1.5 lb |
8.4 | 🛒 Check Price |
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Two Brothers Racing M-2 Black Series Full Exhaust Best Value Full System Full system; stainless steel header and aluminum muffler; P3 PowerTip included |
8.1 | 🛒 Check Price |
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Akrapovic Racing Line Full Exhaust System Premium Build Quality Full system; titanium header and carbon fiber muffler; ECE approved |
8.7 | 🛒 Check Price |
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Vance & Hines CS One Slip-On Muffler Best Budget Slip-On Slip-on; stainless steel muffler; black ceramic coated; includes mounting hardware |
7.8 | 🛒 Check Price |
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Zoom Brute Full Exhaust System Best for Low-End Torque Full system; mild steel header with black paint; aluminum silencer |
7.3 | 🛒 Check Price |
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K&N Intake and Exhaust Combo Kit Best Combo for Power Includes slip-on muffler and high-flow air filter; designed to work together |
8.2 | 🛒 Check Price |
1. Yoshimura RS-9T Full Exhaust System: Best Overall for Power
The Yoshimura RS-9T is widely regarded as one of the best performing full exhaust systems for the Honda Grom. Based on manufacturer dyno charts and owner feedback, it can add 2-3 horsepower at the wheel when paired with an ECU tune, which is significant for the 125cc platform. The construction is top-tier: a mandrel-bent stainless steel header with a CNC-machined billet end cap and your choice of carbon fiber or stainless steel muffler. It also saves about 2.5 pounds over stock, improving both power-to-weight and handling.
However, the RS-9T is not a simple bolt-on. To realize the advertised power gains, you must invest in an ECU flash or a fuel controller like the Power Commander, adding to the total cost. Without tuning, the gains are modest and the bike may run lean. This system is also louder than stock, which may not suit noise-sensitive riders or those in areas with strict decibel limits. If you are looking for a budget option or a simple slip-on, we recommend looking elsewhere.
- Dyno-verified gains of 2-3 hp with proper tuning, per manufacturer claims and owner reports
- Premium materials: TIG-welded stainless steel header and CNC-machined billet end cap
- Includes a removable spark arrestor and USFS-approved for off-road use
Pros: Noticeable mid-range torque increase; Excellent build quality and fitment
Cons: Requires ECU flash or fuel controller for full power gains
2. M4 GP Carbon Fiber Slip-On Exhaust: Best Slip-On for Power
The M4 GP Carbon Fiber Slip-On is a popular choice for Grom owners seeking a quick power and sound upgrade without the complexity of a full system. In our evaluation, the slip-on design makes installation straightforward, and the carbon fiber canister looks great while saving a bit of weight. With the baffle removed, owners report a slightly more responsive throttle and a deeper exhaust note, though actual horsepower gains are modest, typically less than 1 hp on a stock engine.
This is not a product for those chasing maximum power. If your goal is to extract every possible pony from the Grom, a full exhaust system with a tune will yield better results. Additionally, the carbon fiber can is less durable than stainless steel in a drop, and the slip-on alone does not address the restrictive stock header. We recommend this for riders who want a sporty sound and a slight edge in performance without major modifications.
- Designed specifically for the Grom; direct bolt-on without cutting or welding
- Carbon fiber sleeve reduces weight and dissipates heat effectively
- Removable baffle allows adjustment of sound level and backpressure
Pros: Easy installation with basic tools; Noticeable sound improvement and slight power gain with baffle removed
Cons: Power gains are minimal (less than 1 hp) without full system or tune
3. Two Brothers Racing M-2 Black Series Full Exhaust: Best Value Full System
The Two Brothers Racing M-2 Black Series offers a compelling balance of performance and affordability. Based on owner dyno runs and feedback, this full system can deliver around 1.5 to 2 horsepower gains when combined with a fuel controller, making it a strong contender for budget-conscious riders. The stainless steel header and aluminum muffler are durable, and the included P3 PowerTip lets you tweak the exhaust note without tools.
However, the M-2 is not without its flaws. Some users report that the mid-pipe hanger requires bending or shimming for proper alignment, which can frustrate those expecting a perfect bolt-on. The sound, while improved, is not as refined as the Yoshimura, and the power gains are slightly less. If you are willing to spend a bit more for guaranteed fitment and top-tier performance, the RS-9T is a better choice. But for the price, the M-2 is a solid value.
- Includes P3 PowerTip to tune sound and performance without changing the muffler
- Stainless steel header with brushed finish resists corrosion
- Lighter than stock by approximately 3 pounds
Pros: Good power increase for the price (reported 1.5-2 hp with tune); P3 PowerTip allows sound adjustment
Cons: Fitment can be tight; some owners report needing to adjust hanger alignment
4. Akrapovic Racing Line Full Exhaust System: Premium Build Quality
Akrapovic is synonymous with premium exhaust systems, and the Racing Line for the Grom lives up to that reputation. The titanium header and carbon fiber muffler are lightweight and beautifully crafted, reducing weight by over 3.5 pounds. In our research, owner feedback highlights a smooth, linear power increase, typically around 1 to 1.5 horsepower with proper tuning. The sound is deep and refined, not overly loud, and the included dB killer allows legal street use.
However, the Akrapovic is expensive, often costing more than other full systems that offer similar or better peak power gains. For the price, the horsepower per dollar is low, and many owners note that the performance increase is not as dramatic as the Yoshimura. This exhaust is best for riders who value craftsmanship, weight savings, and a refined sound over outright maximum power. If you are on a tight budget or prioritize raw horsepower, we suggest looking at other options.
- Titanium header saves significant weight (approx 3.5 lb over stock)
- Carbon fiber end cap and muffler sleeve with heat shield
- ECE approved; includes dB killer for street use
Pros: Exceptional build quality and materials; Smooth power delivery across the rev range
Cons: High price; value proposition is low for the power gain (1-1.5 hp typical)
5. Vance & Hines CS One Slip-On Muffler: Best Budget Slip-On
The Vance & Hines CS One is a budget-friendly slip-on that delivers a deeper exhaust note and a sportier look without breaking the bank. Installation is straightforward, and the black ceramic coating is durable and heat-resistant. In our evaluation, this is a good entry-level mod for Grom owners who want a more aggressive sound and a slight weight reduction (about 1 pound).
However, do not expect significant power gains. The CS One is primarily a sound and cosmetic upgrade; dyno runs show less than 0.5 horsepower increase on a stock engine. If you are serious about power, you will need a full system and tuning. Also, the muffler is not as quiet as some competitors, so consider local noise regulations. We recommend this for riders on a tight budget or those who only want a sound upgrade.
- Affordable price point for a branded slip-on
- Black ceramic coating resists heat and looks aggressive
- Simple bolt-on installation with included hardware
Pros: Very easy to install; Solid sound improvement over stock
Cons: Minimal power gain; mostly aesthetic and sound upgrade
6. Zoom Brute Full Exhaust System: Best for Low-End Torque
The Zoom Brute is a no-frills full exhaust system that prioritizes low-end torque, making it a favorite among Grom owners who ride in urban stop-and-go traffic. According to owner feedback, the bike feels punchier off the line after installation, and the included re-jetting guide helps carbureted models run correctly. The price is attractive for a full system.
However, the build quality is a compromise. The mild steel header is not stainless, so it can rust over time, especially in wet climates. Many users also report that the header pipe does not align perfectly with the cylinder head, requiring bending or shimming. The power gains are modest overall, and the top-end performance may suffer compared to stainless systems. If you are looking for a durable, high-quality system, we recommend spending more. The Zoom Brute is best for budget-minded riders who are comfortable with some DIY adjustment.
- Designed to improve low-end torque for better acceleration from stops
- Includes a removable spark arrestor for off-road use
- Comes with a re-jetting guide for carbureted models
Pros: Noticeable low-end torque improvement per owner reports; Inexpensive compared to other full systems
Cons: Mild steel header is prone to rust if not maintained; Fitment issues reported; may require modification
7. K&N Intake and Exhaust Combo Kit: Best Combo for Power
The K&N Intake and Exhaust Combo Kit offers a convenient way to improve both intake and exhaust flow on the Grom. The kit includes a high-flow air filter and a slip-on muffler designed to complement each other. In our research, owners report a crisper throttle response and a slight increase in horsepower, typically around 1 hp when combined with proper tuning. The reusable air filter also saves money over time.
However, this kit is not a full exhaust system, so the power gains are limited. The slip-on muffler still uses the restrictive stock header, which is the main bottleneck. For maximum power, a full system like the Yoshimura or Two Brothers is superior. Additionally, installation requires removing the stock airbox, which can be tricky for beginners. We recommend this kit for riders who want a mild performance boost with the convenience of a matched set, but serious power seekers should look elsewhere.
- Engineered as a matched set for optimal air/fuel flow
- High-flow K&N air filter is reusable and washable
- Slip-on muffler reduces backpressure for improved exhaust flow
Pros: Convenient all-in-one upgrade; Noticeable throttle response improvement when used together
Cons: Slip-on muffler alone limits overall power potential compared to full system
Frequently Asked Questions
Will a Grom exhaust add noticeable horsepower?
Yes, but the gains are modest. Based on manufacturer specs and owner dyno runs, a full exhaust system with an ECU tune can add 2-3 horsepower at the wheel, which is a significant percentage increase for the 125cc engine. Slip-ons alone typically add less than 1 hp. Real-world seat-of-the-pants feel is improved throttle response and a stronger mid-range.
Do I need a tune with a new exhaust?
For best results, yes. Without a tune, the engine may run lean, causing overheating and potential damage over time. Most full exhaust systems require a fuel controller or ECU flash to realize the advertised power gains. Some slip-ons can be used without a tune, but the gains are minimal and the air-fuel ratio may still be off.
What is the difference between a slip-on and a full exhaust system?
A slip-on replaces only the muffler, while a full system replaces the header pipe and muffler. Full systems offer greater power gains because they eliminate the restrictive stock header. Slip-ons are easier to install and cheaper, but they provide mostly sound and weight savings with minimal power increase.
Are Grom exhausts street legal?
It depends on local noise and emissions laws. Many aftermarket exhausts come with a removable dB killer or spark arrestor. Some are ECE approved (like Akrapovic) or USFS approved. Check your local regulations. Removing the baffle often makes the exhaust too loud for street use and may result in fines.
Which Grom exhaust is the quietest?
Based on owner feedback, the Akrapovic Racing Line with the dB killer installed is one of the quietest aftermarket options, with a deep tone that is not overly loud. The Yoshimura RS-9T is also relatively tame with the baffle in. Slip-ons like the Vance & Hines CS One can be louder. If noise is a concern, look for systems with a removable baffle and good reviews regarding sound level.
Our Verdict
After comparing specifications, owner feedback, and performance data, the Yoshimura RS-9T Full Exhaust System stands out as the best overall for power gains, offering a proven 2-3 hp increase with proper tuning and excellent build quality. For a more budget-friendly option that still delivers solid performance, the Two Brothers Racing M-2 Black Series is a strong runner-up, especially for riders willing to invest in a fuel controller.
Last reviewed and spec-checked: May 24, 2025. We re-check our picks and listings periodically.
