I have a 2007 214FS, 350MAG, Bravo I (1.50 gear ratio). With a 21" SS 3-blade prop, the tach registers a max RPM of 4300 and top speed of 55 on the speedo. With a 19” SS 4-blade, 4,400 rpm at 54 MPH. The tach is set for an 8 cylinder engine, but simply couldn’t be reading correctly. After the tach stopped working this year, it was replaced and now reads a max of 3,800 RPM at 54 MPH with the same 19” 4-blade prop. The engine is rated for 4,800 to 5,200 RPM. Does anyone have any suggestions on what could be wrong with my tach reading?