FMF Racing · Two-Stroke Off-Road

FMF Fatty Expansion Chamber

The pipe that built FMF's reputation in the dirt — tuned to fatten up the bottom-to-mid powerband on your 250/300 two-stroke for traction you can actually use. ***DEAL IS VALID FOR USA AND CANADA.

SKU 55505907000

The Fatty isn't about chasing peak horsepower on a dyno sheet — it's about the part of the powerband you live in on a trail. FMF engineers the chamber volume and taper to broaden low-to-mid output, smoothing out the abrupt hit of a big-bore two-stroke into linear, hook-up power. The result is a bike that lugs through technical sections without fouling, drives off the bottom out of corners, and stays composed when the terrain gets nasty.

Every Fatty is CAD-designed and hand-welded in the USA from heavy-gauge nickel-plated steel, then built to bolt straight on using your bike's OEM mounting points. It's the off-road standard for a reason: proven power, proven durability, and a fit that doesn't fight you in the garage.

Why riders run it

Broader low-to-mid powerSmoother, more tractable delivery dialed for trail, enduro, and woods riding.
Sharper throttle responseMore torque off the bottom and cleaner roll-on when you need drive.
Built in the USACAD-engineered and hand-welded for consistent, repeatable performance.
Heavy-gauge steelNickel-plated construction made to survive roost, rocks, and tip-overs.
True bolt-on fitMounts to OEM hangers and points — no fab, no fuss.
System-readyEngineered to pair with FMF silencers (Turbinecore 2 / Q-Stealth) for a complete setup.

Specs

Component	Expansion chamber (pipe only)
Material	Heavy-gauge nickel-plated steel
Engine	250 / 300 two-stroke
Power character	Broad low-to-mid, off-road tuned
Fitment	KTM, Husqvarna & GASGAS · model years 2019–2023 (see chart)
Installation	Direct bolt-on, OEM mounting points
Made in	USA
SKU	55505907000

Heads up: This listing is for the expansion chamber (pipe) only. Confirm your exact model, year, and market in the fitment chart below before ordering.

Fitment Chart

KTM

2023
250 EXC	EU
250 EXC Six Days	EU
250 XC-W	US
300 EXC	BR · EU
300 EXC Erzbergrodeo	EU
300 EXC Six Days	CN · EU
300 XC-W	US
300 XC-W Erzbergrodeo	US
2022
250 EXC TPI	EU
250 EXC Six Days TPI	EU
250 SX	EU
250 XC TPI	US
250 XC-W TPI	US
300 EXC	BR
300 EXC TPI	EU
300 EXC TPI Erzbergrodeo	EU
300 EXC Six Days TPI	ASEAN · CN · EU · PH
300 XC TPI	US
300 XC-W TPI	US
300 XC-W TPI Erzbergrodeo	US
2021
250 EXC TPI	EU
250 EXC TPI Six Days	EU
250 SX	EU
250 XC TPI	US
250 XC-W TPI	US
300 EXC	BR
300 EXC TPI	EU
300 EXC TPI Erzbergrodeo	EU
300 EXC TPI Six Days	CN · EU
300 XC TPI	US
300 XC-W TPI	US
2020
250 EXC TPI	EU
250 EXC Six Days TPI	EU
250 SX	EU · US
250 XC TPI	US
250 XC-W TPI	US
300 EXC	BR
300 EXC TPI	EU
300 EXC Six Days TPI	EU
300 EXC TPI Erzberg Edition	EU
300 XC TPI	US
300 XC-W TPI	US
300 XC-W Six Days TPI	US
2019
250 SX	EU · US
250 XC	US
300 XC	US

Husqvarna

2023
TE 250	EU · US
TE 250 Heritage	EU
TE 300	AR · EU · US
TE 300 Heritage	EU · US
2022
TC 250	EU
TE 250i	EU · US
TE 300i	AR · EU · US
TE 300i Rockstar Edition	EU · US
TX 300i	US
2021
TC 250	EU
TE 250i	EU · US
TE 300i	EU · US
TE 300i Rockstar Edition	EU · US
TX 300i	US
2020
TC 250	EU
TE 250i	EU · US
TE 300i	EU · US
TE 300i Jarvis Edition	EU · US
TX 300i	US
2019
TC 250	EU
TX 300	—

GASGAS

2023
EC 250	EU · US
EC 300	EU · US
EX 250	US
EX 300	US
MC 250	EU
2022
EC 250	EU · US
EC 300	EU · US
EX 250	US
EX 300	US
MC 250	EU
2021
EC 250	EU
EC 300	EU · US
EX 300	US

FMF Brand

FMF Q4 SILENCER KTM/HUSQVARNA/GASGAS 250-501 2024 - A49005981004

FMF POWERCORE 2.1 SILENCER 250/300 SX/XC 23-24 - KTM POWERPARTS - A44005979002 - KTM/Husqvarna/GASGAS

FMF TITANIUM POWERCORE 2.1 SILENCER 250/300 SX/XC 23-24 - KTM POWERPARTS - A44005979003 - KTM/Husqvarna/GASGAS

FMF TURBINECORE 2.1 SILENCER 250/300 SX/XC 23-24 - KTM POWERPARTS - A44005979004 - KTM/Husqvarna/GASGAS

FMF-FACTORY - 4.1-RCT-MUFFLER 450/500 22-24 - A48005981003 - KTM/Husqvarna/GASGAS

FMF Fatty Expansion Chamber Pipe — KTM Husqvarna GASGAS 250 300 2-Stroke (55505907000)