DOMA Expansion Chamber for BETA RR 250, RR 300, RX 300 2013-2025

The DOMA 100415 expansion chamber is designed for BETA RR 250, RR 300, RX 300 from 2013 to 2025. On a two-stroke, the expansion chamber isn't just a pipe: its cones send back a pressure wave that fills the cylinder better at the right rpm. Its shape gives the engine its character, and a dented pipe costs power.

Key features

• Handmade in Calais, France.
• 1 mm raw steel, laser-cut parts, pressed and then welded on a jig.
• Developed on the dyno and on the track.
• Works with the stock silencer or a Doma silencer.

Specifications

• Brand: DOMA
• Manufacturer part number: 100415
• Engine: 2-stroke

Who is it for?

• Stock pipe dented or cracked after a crash.
• Looking for more response and more power.

Good to know

Competition use only: this pipe is not road-legal.

Fitting tips

1. Reuse the stock connecting O-rings if they're in good condition (not included), or fit a new exhaust gasket.
2. Offer up the pipe without forcing it, fit all the mounts, then tighten.
3. Warm up the engine and check for leaks at the joints.
4. Check the colour of the spark plug after the first few rides.

Why DOMA?

A French workshop based in Calais since 1992, Doma Racing designs and handbuilds two-stroke expansion chambers and silencers. A 125 world title in 2000 with Grant Langston and original equipment at KTM: a brand run by two-stroke enthusiasts.

Spare parts and items to plan

• Exhaust gasket : ATHENA M753004300094 · ATHENA S410060012011
• Spark plug : NGK 3961 · NGK 90982

Frequently asked questions

Do I need to change the silencer?
No: the pipe works with the stock silencer or a Doma silencer.

Is it road-legal?
No: for competition use on closed circuits only.

Compatibility

Check the exact model and year of your bike in the list below before ordering.

Fits:
BETA RR 250 2025
BETA RR 250 2024
BETA RR 250 2023
BETA RR 250 2022
BETA RR 250 2021
BETA RR 250 2020
BETA RR 250 2019
BETA RR 250 2018
BETA RR 250 2017
BETA RR 250 2016
BETA RR 250 2015
BETA RR 250 2014
BETA RR 250 2013
BETA RR 300 2025
BETA RR 300 2024
BETA RR 300 2023
BETA RR 300 2022
BETA RR 300 2021
BETA RR 300 2020
BETA RR 300 2019
BETA RR 300 2018
BETA RR 300 2017
BETA RR 300 2016
BETA RR 300 2015
BETA RR 300 2014
BETA RR 300 2013
BETA RX 300 2025
BETA RX 300 2024
BETA RX 300 2023