When I built my first motor on my 2000 fastech 271 it dynod 693hp. Boat would run right at 80 on gps with 100 gallons of fuel and 4 people onboard spinning a box stock 28 pitch bravo 1 prop and a standard length 1.50 bravo Xr. Current motor is 713hp and it is way underpropped . Get 80+ out of it running the same 28p bravo one prop with plenty of throttle left. Tried running a bigger prop but the time to get up on plane is soooo slow so 28p is good all around. Tried running a 5 blade but the hull does not like it. Jeff wurl

By the way when my boat had the box stock 502 mag I could get 68 mph on gps with a labbed 28 pitch bravo one prop and the 1.65 drive . You have a motor problem or you motor is not producing anywhere near 675 hp. Jeff wurl