KTM · PowerParts · Exhaust systems
The KTM FMF Factory Fatty Expansion Chamber is a KTM PowerParts expansion chamber designed for 2-stroke offroad exhaust setups, built to deliver a full sound and improved power delivery. This is a purpose-built component for riders looking to refine exhaust performance with a proven expansion chamber design.
Part number A40505907001 features extra strong sheet steel and an untreated surface. For a matched setup, a combination with an FMF silencer is recommended. Vehicle compatibility is listed for the models shown in the compatibility information below.
Performance
Engineered to support better power delivery, this expansion chamber is aimed at riders who want a stronger, more responsive feel from their 2-stroke offroad exhaust system. It’s a focused upgrade for performance-minded setups where exhaust tuning plays a key role in how power is delivered.
Construction
Constructed from extra strong sheet steel for a robust build suited to offroad use. The durable construction is intended to handle the demands placed on an expansion chamber while maintaining the core characteristics needed for consistent exhaust performance.
Design
Finished with an untreated surface for a raw, purpose-driven look consistent with its functional design. This finish keeps the focus on the expansion chamber’s construction and performance intent without added surface treatment details beyond what’s specified.
As part of KTM PowerParts in the Exhaust systems > 2-stroke Offroad category, the FMF Factory Fatty Expansion Chamber is designed as a targeted exhaust component upgrade. It is described as delivering full sound and better power delivery, making it a strong option for riders tuning their offroad 2-stroke exhaust system toward performance-focused output and character.
For riders building a complete exhaust setup, a combination with an FMF silencer is recommended. Pairing components as suggested can help keep the exhaust system aligned with the intended configuration of this expansion chamber, especially when dialing in overall performance and sound characteristics for offroad use.
| Part Number | A40505907001 |
|---|---|
| Product Line | KTM PowerParts |
| Category | Exhaust systems > 2-stroke Offroad |
| Approvals | AMA Amateur, CCCUO |
| Model — Model Years |
|---|
| 65 SX — 2024–2027 |
Vehicle compatibility as captured from KTM for article number A40505907001.
KTM approval notice: AMA Amateur racing sound compliant.
KTM approval notice: Closed Course Competition Use Only.
