2.5. For GB3, British GT and British Touring Car Championships the Noise test shall be conducted as set out within these regulations with the engine running at 3 / 4 maximum speed the Noise level meter at a height of 0.5 metres above the ground(± 0.1 metre) located at 45 ° to and 0.5 metres distant from the exhaust with a maximum permitted Noise level of 118dB( a).
2.6. Temporary Silencers by-pass pipes or the inclusion of temporary parts to achieve silencing requirements are prohibited. Officials may refuse to carry out Noise Checks on vehicles utilising temporary parts in exhaust systems. Organisers are empowered to disqualify in such situations.
2.7. Circuit / Venue owners / Organisers may impose additional restrictions including in the Official Documents.
3. Noise Test Requirements( Appendix 13 Chart 1) Noise testing should be carried out BEFORE taking part in any Competition.
3.1. Specific Regulations apply to Rally( Chapter 13) and Kart Racing( Chapter 18). 3.2. The time and location of Noise testing should be advised to Competitors prior to the Event.
3.3. Measurements will be made at 0.5m from the end of the exhaust pipe with the microphone at an angle of 45 ° with the exhaust outlet and at a height of 0.5 to 1.0m above the ground.
3.4. Where more than one exhaust outlet is present the test will be repeated for each exhaust and the highest reading will be used. In circumstances where the exhaust outlet is not immediately accessible the test may be conducted at 2.0m from the centre line of the vehicle at 90 ° to the centre line of the vehicle with the microphone 1.2m above the ground.
3.5. Measurements should be made outdoors with no large reflecting objects( e. g walls etc.) within 3.0m( in the 0.5m test) or within 10.0m( in the 2.0m test).
3.6. Background Noise levels should be at least 10dB( A) below the measured level.
3.7. Where possible measurements should be taken as close as possible to the vehicle at the defined distances to avoid background Noise.
3.8. Cars of Periods A to D falling within Sections C and D should run engines at two thirds maximum RPM. 3.9. The 2.0m test can be made from either side of the Vehicle. 3.10. The highest reading registered being the one needing to comply with the maximum Noise requirements.
3.11. It is stressed that all participants in Motor Sport Competitors Officials Marshals etc. should be aware of and protect themselves from Noise.
Motorsport UK 2025 National Competition Rules Version 11
Chapter 7 Appendix 8- Exhausts Silencing and Noise Testing 275