Hi Ben! You can make and manage appointments for appeals on vehicle modification and inspection matters at LTA Customer Service Centre, 10 Sin Ming Drive, via their Digital Services at the following link: https://go.gov.sg/lta-eappointment
For the exhaust system, which consists of the exhaust manifold, catalytic converter and muffler, is used as part of a vehicle's exhaust-emission control system to ensure that the exhaust emission meets environmental standards. Before modifying the exhaust system, you need to get LTA’s approval by submitting these for evaluation:
Certification from the product manufacturer stating that the proposed aftermarket exhaust system is suitable for the make and model of the vehicle
Test reports from LTA- or NEA-recognised test laboratories to show that the aftermarket exhaust system, when fitted to your vehicle, complies with noise and exhaust emission standards for your vehicle model
You are not allowed to remove catalytic converters and mufflers, as it will adversely affect the exhaust emission characteristics of the vehicle.