Pipe sizes and engines

Ok pipers,
I have a question. It seems that the thing to do nowadays is to go to a larger pipe for a specific engine size. Where as before a 40 size pipe was used on a 40 engine, and a 60 size pipe on a 60 engine. I have an OS 40VF and a Brian Eather #5 pipe for next year's airplane. I was told that my engine would love the larger pipe. I also see some posts that guys are using the 65 pipe on the 61 engines. Can someone explain to me why my engine is going to love the 40 to 60 sze pipe and why we seem to be going to larger pipes for a specific engine size. I have never run a pipe before and so I'm very new to this way of flying. Thanks in advance.

The first tube mufflers we got from Art for our 35 FP used the same size chamber he had been using on the Fox 35 and they didn't work well. Too restrictive. Increasing the length 1/4 inch made the day. With pipes the length is a determining factor, so increasing the volume (diameter) or opening the stinger can allow for more power.

We tried the 65 pipe on Matt's 61 at the advice of Billy Werwage and Randy Smith, and they were right. It did allow more power. It is a little larger diameter than the 61 pipe, but Matt's plane would take it. You might have noticed that not only are the newer pipes larger in diameter, but the engines are also getting noisier. The opening of the stinger has been increased to allow the exhaust to escape better. One thing you will need to watch is that little "rubber ducky" at the end. It will rob power. Some of the newer pipes that Billy is producing have the stinger coming out at an angle so you don't need to add that deflector. This, too, adds less restriction to the power of the engine.

My only question is, "If the 65 pipe improves the 61 engine by increasing the volume, is the 65 pipe now maybe too small for the 65 engine?" Of course, it depends on the size props you want to turn and so forth. You can now run a 14 inch 3-blader with either. And if you are running the smaller props or wanting more fuel efficiency, maybe the smaller pipe is still the way to go.

Leonard Neumann

It doesn't. My reference (not always clear) was for the need for more power. Just like the size of the venturi, you don't need to go to a larger venturi if your present one is working fine. Or more nitro. Or bigger pipe. If you have a need for more power, then you can up the venturi size (to a point) and, perhaps, benefit from a less restrictive pipe. But the pipe, like the venturi, is going to have some point where going bigger won't help and will even hurt. Everything works together and the weakest link is still the weakest link.

Leonard Neumann