Hello, I would like to understand the function and the operation of the exhaust butterfly valve inserted in the left exhaust pipe of my Thunderbird Commander. If for whatever reason this is efficient, why only in one of the pipes, why not in both of them. Any advice appreciated.
Thanks Helmut Visor. In the meantime I found a quite reasonable explanation. QUOTE --- The purpose of this system according to the motorcycle manufacturers’ marketing departments is to create back-pressure at lower RPM’s to increase torque. Unfortunately, this probably isn’t the real reason; the true purpose of the exup valves is to meet noise and emissions regulations. The exhaust valves are partially closed at idle and low rpm to reduce noise, and closed again at the upper RPMs to meet peak noise and emissions regulations. The proof of this has been shown on the dyno where removing the valves and retuning the engine creates a flatter better torque curve. --- UNQUOTE It still doesn't explain why only one system I/o two :-(
Welcome! Mabe this link will help explain. It's a tad technical but covers most of it https://www.bennetts.co.uk/bikesocial/news-and-views/features/bikes/how-does-an-exhaust-work
Hi, originally i thought that disconecting the cables would keep the valve open, but it doesn't, it keeps the valve almost closed. So then i opened the valve all the way open by some twisting and bending of metal. The diffrence was crap low rpm power, was horrible, so, i put the cables back on, and hey presto, power came back, more torque and a smoother running engine. When the valve was almost always closed it felt better than always open, but fell on its feet because the gases couldn`t escape after 5,500 rpm, making it feel like shite, had loads of torque because of the back pressure/SCAVENGING effect down low but high rpm failed. That valve is there for a very good reason, so personally i would leave it well alone or buy the akra slip on with the valve. In England the slip on or muffler is called a silencer for a reason, to serve the purpose of silencing noise, not emissions, as many are led to believe. The CAT, silencer and valve all have different applications, that work in perfect harmony in stock form, for stock fueling.
