When running my wife's 1" Pacific last fall, we noticed a hard sounding exhaust and the engine was firing hard even when hauling minimal load on flat ground. Reviewing the problem, the exhaust tee was just a straight through tee that didn't divert the exhaust up to the stack and the cylinders were fighting each other.
With minimal space available and a short turn around needed, I turned to 3D CAD and metal 3D printing to fix the problem. A design was made up in SolidWorks to allow separate flows until the exhaust is in the vertical orientation and to review the cross section throughout to not cause a pinch point. The picture below is the end result of the modeling.
- Cross Section View
The model was sent to Shapeways and printed in bronze fused stainless steel. Upon receiving the part, a few dimensions were undersized and needed to be bored out. Note the brass pipe on top was not 3D printed and was pressed in and Loctite 680 was used to retain it.
- Boring Hole
After boring, Teflon sleeves were pressed in and bored for the flanges to better seal the part and allow for movement when heated/cooled.
- Teflon sleeve
The final result was exactly as designed and fit well within the engine.
- Final Assembly
The blower and exhaust ring were reattached to the top and the engine was ran on air to review the performance.
- Installed in engine
Where previously the exhaust was loud and noticeable, the bark was drastically reduced (with no load) but the airflow on the exhaust was increased. (I wish I took airflow measurements before the modification to see the change) The engine is going to be fired up this Memorial Day at St. Croix and will advise on the performance differences (as well if the wife approves of the fix
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