How many of you have spent the money on a Pitts style myffles to find out the engine did not run like it did with the stock muffler. I also had this problem and came up with a fix for my Evolution 1.0 on my F6F. My Bisson Pitts style muffler had two 3/8 discharge pipes, that look great, but some nitro engines need back presure to run as designed. The stock Evolution muffler has one exhaust outlet. With the pitts muffler having two exhaust outlets, it lost the needed back presure, and ran very poor.

Some people have just plugged the one pipe but it was important to me that both pipes breathing exhaust. I went down to my local auto parts store and picked up a 6" 1/8" brake line with the fittings on. I cut the pipe and removed the two needed fittings. The outlet of the stock muffler is 3/8,( or very close to it) and the ID of the two 1/8 fittings when added together are 3/8, (same size of the single stock exhaut outlet)The threads of the 1/8 fittings will thread right into the pitts exhaust tubes. I cut off the hex heads of the fittings slotted them on the end so I could use a flat bladed screw driver the install them. I first ran them into the tubes, cutting threads in the alumn of the tube, and then removed them. I added some red locktight and then reinstalled them. What this did is reduce the two exhaust tubes size on the pitts muffler to equal the same ID on the single tube on the stock muffler. This brought back the needed back presure for the engine to run and also gave me both pipes discharging exhaust. It now run's great in all operating ranges.