4.3 to 5.7 swap
 

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.

Thanks
Ryan

I would run the 1.5. It's the drive made to run with that engine. A 1.5 drive would run faster than a 1.8 using the same prop at the same engine RPM.

gear ratio also moves your power bands per rpms

there is reason why marine apps have different gear ratios for different engines.

For the 5.7 Merc did use 1.47 and 1.50 and a 1.65 if I recall the 1.65 was for the 210 hp 5.7 / 350 CID Mercruiser..

Yes you want the 1.5.

Thanks for the advice. What I meant by the same prop was, a different pitch for the different ratios, but in the end the final ratio was the same. I understand what you are saying.

I know my buddy has a 5.0 in his Crownline and it has the 1.65 ratio as well.

I will swap the upper unit at the same time I put the engine in. Thanks for all the advice.

Ryan