Chainsaw Repair

Right now I am experimenting with a 372XP top exit muffler as my test subject. I am going to try two approaches. First a 0.800 ID pipe done in the usual manner, sticking out the bar side of the muffler. I have done up three of these all with different length pipes. Pipe lengths are 1.5, 1.75 and 2.25 inches. All with the same internal protrusion depth.

It dawned on me that 0.800 ID pipe may be a little large when combined with the factory exit. So, I made up a copper blocking plate that goes where the screen would go. This way I can run the saw with modified mufflers with and without the factory exit being open. I will post some pictures of the mufflers later in the day, so that everyone can inspect. The outlets are thin wall steel pipe.

Next I am going to make up a couple of 'tuned pipe' versions e.g. the stinger on a piped saw. There are plenty of expansion chamber design programs out there but unfortunately there are none for the box style mufflers used on chainsaws. So this will present a lot of messing around. There is a secondary challenge here in that you cannot have 5-7 inches of pipe sticking out the side of a work saw. However looking at the pictures 660 posted, it is possible to hide most of the length inside the muffler just as was done on the 550 pictured. For a tuned pipe to work correctly and deliver results it has to be the only exit on the box. Also if using 0.800 pipe that pipe cannot be within 0.800 from any corner or internal wall of the muffler. The pipe does not have to be straight either, it can be curved like a pretzel if that gets the length you need inside the box. Looking into some flexible steel pipe similar to the jacket on old BX cable to try this with.