ORIGINAL: AndyW
I wonder if a collector ring with much more volume and an exhaust stub would help. There's lots of room. I'd also have a few cooling fins built in.
My last post assumed that the sub piston induction was still present, which the original post obviously states that it has been eliminated, but most mufflers on 'racing' designs do rob power regardless due to back pressure.
Simply providing a greater volume for the exhaust gases to expand into will help but Ihighly doubt that finning the collector will do much at all.