I hope this is not the same design that has been creating too much back pressure and causing seized pistons. 

About a year ago I had a customer send me his engine that had a seized piston.  He said this was the second piston that had seized since he installed the extra long silencer on his Q pipe. 

I had the customer send me his extra long Shearer silencer to inspect.  Flow test did not meet my criteria or expectations.  I built him an extra long HPR silencer for his Q Pipe.  Piston seizures stopped and the customer said it was quiter than the extra long Shearer silencer. 

I built a jig and can make more if anyone is interested.