OK,just checking.Its true about the muffler that antique stated.Even the baffles reduce flow.Thats why pitts are hollow,also why there louder.The baffles mix and churn the air to reduce the poping effect.Just for a reference,i just converted a shindaiwa 27,used,but it said 140lbs? compression on case.Im at 3000 MSL,i used a G23 carb rotator that fits ok.I used a 11mm carb,2 needles,stock muffler.I am spinning an APC [email protected] ill do tomorrow is put my G23 muffler on it and see if it helps any.[Its hollow].60 -70 lbs is a little low.