Ok, now that I have your attention - I have a OS .61FX that I'd like to put a pitts style muffler on and have one laying around from a ST G-90. Haven't measured the bolt pattern yet, but was wondering if it would work. What are the requirements when it comes to swapping mufflers between manufacturers and sizes. Is there a volumetric chart anywhere stating the required muffler 'volume' for a specific size engine...almost like a prop-chart?

Can I measure the standard muffler that came with my OS, calculate the volume and do the same for the Pitts style to ensure it's 'about' the same. Any issues I may be missing.

If all else fails I'll just look to buy one.