RE: JBA .56
Today (New Years Day) I did a little more testing on the JBA .56. I had already tested the Jett-Stream tuned muffler and found it wasn't very helpful on the JBA. I decided to make a quick check with a Tower muffler and the E-3020 from the OS .55AX.
Muffler weights:
JBA: 5.5 oz (This was a different JBA .56 muffler from the one I weighed before and it turned out to be .2 oz heavier)
Tower: 3.8 oz
OS E-3020: 4.2 oz
Notice that the JBA muffler is sort of a slug. When I started weighing Ed's engine and noticed the JBA was really heavy, it gave me the idea to try other mufflers. The JBA is even heavier than a Jett, so it's too bad the Jett didn't work very well.
rpm testing
My Tower mini tach was acting flaky so I used a Thunder Tiger tach. The rpm on the control prop were a few hundred lower than with the Tower tach, but all you reall need is the relative numbers.
Prop 12.25-3.75 APC 3D prop
JBA muffler: 12,700 (This is 300 rpm lower than the original test, but with a different tach)
Tower: 12,300
OS E-3020 12,300
The JBA muffler showed a higher rpm on the first run and I duplicated it again after running the Tower & OS muffler just to make sure. Both times it peaked at 12,700, so I am confident that the JBA muffler on the JBA .56 is faster.
Here's a couple more of my thoughts. I may try the JBA muffler on the OS .55 to see what happens. The other thing is the JBA .56 is really has .579 cu. in. dosplacement, so it's a .58. It may need a 61 sized muffler. It looks in the photo showing the Tower muffler on top and the JBA .56 muffler on the bottom, that the JBA may be slightly larger. The larger size of the forward casting is probably what is adding the extra weight. The second photo shows the JBA on the test stand with the OS and Jett-Stream mufflers.
I did see a thread, maybe a couple of years ago, on some testing of the Tower muffler on an OS .50SZ. He had access to a machine shop and had a longer center section made from thick walled tubing. After he lengthened the center, he noticed an rpm increase.