RE: CARF-Models P-47 Thunderbolt
Jack,
The smooth ends are just slightly over 20mm in dia. This means they slip right over the Moki exhaust stubs. I cut slots in the copper pipe so that the hose clamps could crimp them down tight around the Moki stubs.
At the very end of the pipe, the diameter is slightly larger (too large to fit on Moki stubs) and it is these end pieces I cut off and used for the angle cut exhaust outlets, silver soldering them to the ends of the copper pipe.
I have not yet run the engine with these 12 inch extensions, so cannot attest to how they affect performance.