I've never tried playing around with any boats trying to crank up their speed (been faithfull to stock equipment for the last 10 years). Anyways I've got a Yamarin 5400 Big Ride coupled with a 2-stroke 50HP Yamaha Pro motor (don't remember what year/model).<br /><br />I'm going to put a 90HP 4-stroke engine on this boat and that would leave my old motor useless. Now a 50HP Yamaha Pro looks exactly like a 75HP Yamaha at the outside and the inside. I wonder if there are any differences between these (except that something would be limiting the 50HP engine) and would it be possible to turn this engine to a 75HP one by bying some 75HP spare parts and replacing the stuff in my 50HP engine with these?<br /><br />I'm going to buy a new prop and a light weight catamaran. What modifications should I do to get maximum speed? What are the optimum RPMs? Should I change the stock prop I get with my 90HP 4-stroke and does it help a lot?<br /><br />Thanks in advance<br />Edvard
