What's interesting is that when I researched putting my 0290 exhaust onto my 0320 conversion, I went to the new market & found that the standard exhaust systems sold were listed as fitting both the 0290 and 0320, so I don't believe there's really any difference. For the time I had my cub with the 0320 (sadly, wrecked it this last spring), performance was (so far as I could tell) not an issue. I had been ready to put the hod rod muffler on it (didn't get that done before losing the airplane), which according to anyone I talked with about it, would enhance performance (as well as get rid of the AD on the standard muffler).