I have a 2004 Crownline 180 and I am installing a 260hp merc 5.7. My boat currently has the 190hp 4.3 with the 1.8 gearing, but I have the option to run the 1.5 gearing that came with the 5.7. I have read a lot of things that said the 1.8 will work fine and they make plenty of props for it. I have also read that with equivalent props, the 1.8 will actually net me a higher top speed. I was wondering what everyone else thought of this. I plan on pulling the motor in a week or so. Thanks for all the help in advance.
years ago I installed a 305 in place of an inline 6, with an older MerCruiser I drive. I used the original drive and propped it for the correct wide open throttle RPM. It has worked fine for 20 plus years, but if I had an 8cyl gear ration drive I would install it in a second just because the boat would have "better manners" while maneuvering at slow speed. Plus, you will have more prop choices if you are using a more mid-range pitch. The engineers at MerCruiser selected the engine specific gear ratios for a reason.
In my opinion, use the drive with the 8cyl gear ratio if you have one available. Overall you should be happier with the result.