Looks impressive. I noticed that there are baffles in the tailpipe, [Try pushing a long rod up the back end?], probably situated through the pipe, so there will be a fair bit of back pressure, which would cause this. I'm not sure if the same thing happens with bike engines?
I wonder if the baffles are responsible for the low bhp? Just a thought!
Black & Tan M3W, Caterham CSR, Mini Cooper D Clubman, Macgregor 26M, Powabyke.