A friend is building a scale SRE and we decided to make the exhaust as realistic as possible, hiding it inside the radial cowling.
On the real aircraft, the exhaust exits via two pipes under the cowl.
As shown in the pictures, the exhaust enters via the center tube - it's connected to the 4-stroke engine with a silicone flex tube.
Fabrication was quite simple. I made it from six separate parts, each machined from 6061 bar stock.
Bob Z.