Factory4.1 SL (slip-on)

The Factory 4.1 is FMF Racing’s premier performance exhaust system incorporating every conceivable technological advantage taken from the thirty plus years of our racing heritage. Featuring proprietary trade secrets such as the uniquely designed Chamber Core and exclusive PowerBomb header for full systems, the Factory4.1 is guaranteed to produce more horsepower throughout the entire RPM range! The impressive gains observed on the dyno do not give justice to the power that’s put to the ground. After all, would Factory KTM or Yamaha of Troy use anything but the very best performing exhaust systems?

More than “just another race muffler”, the Factory 4.1 has a long list of features that may go unnoticed. FMF pioneered “Factory Forward” engineering; moving the muffler further forward in the frame, shortening the midpipe and muffler length to centralize mass and lower the center of gravity for improved handling. Take the angle cut canister – a distinct look that separates FMF from the pack. There is our exhaust port flange (full systems only) that transmits less vibration and puts less tension on the header. There is our proprietary muffler packing incorporating various substrates of wire mesh, high density fabrics and advanced sound absorption material – FMF’s packing is arguably the best in the industry. Where others skimp, FMF beefs it up to give you unmatched reliability.

Anyone can make a bolt on system, but not anyone can give you the innovations and patent pending technology FMF offers or the quality from making each exhaust ourselves. FMF Racing is performance. Bolt on a Factory 4.1 and FEEL THE POWER!

Factory 4.1 SL – Titanium (Ti) Midpipe
Titanium slip-on muffler with titanium midpipe; same muffler as Factory 4.1 system. Available in natural titanium or blue anodized finish. Fits stock or FMF header.

Factory 4.1 SL – Stainless Steel (S/S) Midpipe
Titanium slip-on muffler with stainless steel midpipe. Available in natural titanium or blue anodized finish. Fits stock or FMF header. - Boosts low-mid torque, broader powerband, more over-rev.

- Features exclusive proprietary Chamber Core technology.
- Factory Forward Engineering centralizes mass, improves handling.
- All titanium construction - canister and endcaps; choice of mid-pipe.
- Made from premium quality American materials.
- Customize with performance tuning inserts and spark arrestor module.
- Meets AMA sound requirements on most models; inserts available for others.