FMF - KTM Factory Fatty Expansion Chamber

KTM – FMF Factory Fatty Expansion Chamber

The FMF Factory Fatty Expansion Chamber brings factory-level performance to every ride. Inspired by the original “works” cone pipes used by professional race teams, the Factory Fatty is hand-built with premium materials and meticulous craftsmanship to deliver a smoother, broader power curve across the entire RPM range. Whether you’re charging through tight singletrack or hitting wide-open straights, this pipe delivers more low-end torque, stronger midrange pull, and a longer over-rev for total control and confidence.

Constructed from lightweight 20-gauge steel for the main body and 19-gauge steel at the header, the Factory Fatty strikes the perfect balance between durability and responsiveness. Each pipe features hand-pounded seams for unrestricted flow and precision fitment with included O-rings on most models. The result is the unmistakable performance feel that FMF is known for — crisp throttle response, full-bodied power delivery, and a raw, race-ready sound.

Pair it with an FMF silencer for maximum performance and the kind of throttle feel that makes two-strokes come alive.

Why We Like It:

The Factory Fatty gives your KTM that pure, mechanical punch every rider loves from a two-stroke — crisp off-idle torque, strong midrange pull, and that hard-hitting top end that never quits. It looks as good as it performs with its raw steel finish and hand-built quality that screams factory race bike.

Why It’ll Work for You:

This pipe improves how your KTM runs across the whole RPM range. The thinner steel body lets the engine respond faster, and the cone shape helps the exhaust flow more smoothly. That means steadier power from low speed through high revs. It’s built strong enough for rough riding, fits easily without modification, and makes throttle control more predictable when you’re climbing, cornering, or getting on the gas out of turns.

Key Features:

• Broadens and smooths power delivery across the entire RPM range
• Increases low-end torque, midrange pull, and over-rev power
• 20-gauge steel body and 19-gauge header for optimal strength and response
• Hand-pounded seams for smooth internal flow
• Includes O-rings for proper sealing and easy installation
• Raw “works” style finish for authentic race look
• Designed to perform best when paired with an FMF silencer
• Proven on KTM two-strokes in off-road and motocross applications