Weird thing. I tried a Pitts muffler on my converted 180, muffler pressure was barely measureable and didn't rise with rpm hardly at all. I blocked one of the two exhaust outlets, pressure rose up to approx .25 psi but same problem, no pressure rise above 1/2 throttle. I guess I'll have to restrict the one outlet until pressure comes up further. Hoping for at least .50 psi but I suspect I'll not see much of a pressure rise with rpm. There are two nipples on the muffler, one for tank pressure and I suppose the other for smoke, even though there is no nozzle that hole is located close to the exhaust port. The Pitts may not be a good candidate for this gas conversion program.