Does the muffler inlet and outlet have to be the same size as the tubing?

Yes, the muffler inlet and outlet should ideally match the size of the tubing for optimal performance and to maintain proper exhaust flow. Using mismatched sizes can lead to backpressure issues, reduced efficiency, and potentially affect engine performance. However, in some cases, slight variations may be acceptable depending on the specific system design and desired sound characteristics. Always consult manufacturer guidelines for the best results.