Thread: Mufflers and Exhaust Pipes of different size

My Haflinger has a bike muffler that will not be legal as it exits in front of the rear wheel. As it might take me some time to source a proper muffler I am thinking about making up a muffler and tail pipe. The issue is the muffler sits vertically in the car and there is not room for it to mount under the car as you would in other vehicles.

What I want to do is use the smallest 'hot dog' muffler onto the current exhaust pipe and then plumb a tail pipe out the back.

The main issue I face is the smallest size inlet for the hotdog that I can find 40mm where the Haffie exhaust is 32mm. Now matching the pipe to the muffler is not an issue but I have no idea what it is likely to do to engine performance. Clearly if the muffler inlet was smaller than the exhaust pipe the engine would be strangled somewhat but as it will be larger, can I assume there will be no issues for the engine - will the reduced back pressure be an issue. Likewise the outlet of the muffler will be a bit large so making the tail pipe smaller (32mm) is that likely to cause issues with engine performance.

Cheers

garry

Any discontinuity in the exhaust pipe will result in reflections of the pressure pulse. If you make the transition gradual it will be better than a step change.

I doubt it will make much of a performance difference, such that you would feel it.