But S flow also straight through muffler, only it return and then out again as in S. Why got so much back pressure?No i think the problem was caused because my s flow (jian hang) and mid swirl bullet (kent wong exhaust) both have the function of storing backpressure in the exhaust system n cause too many pressure in the exhaust system not allowing the pressure to exit smoothly n my rpm cant rise smoothly.... if im correct la