I'm running a 17ft v hull. 115hp v-4 2 stroke 1978. the current prop is a 19 pitch. I have cranked her up to 6500 rpms and there was some room left to go. Is my tach way off or can this motor turn that many rpms. The hole shot is good and I can cruise at 4000 and keep it on plane. The speedometer says that I am only going 30 mph at 6000 rpms. I am looking at replacing the prop soon because the one on the boat looks orig. any sugg. thanks in advance.