What octane gas will I have to run in a stock 2000 7.4 MPI ? The guy I bought it from said 87 should be ok. I am wondering how much difference if any a higher octane will make .

87 or 89 is fine. I highly doubt it will make any diff. on that engine to run 91+

Happy boating

power will go down with the higher octane fuel. the computer program and engine are configured for 87 octane.

X2

and 91 will make your transom sooty.

It was designed for 87 octain, the important thing is keep the fuel fresh. Only fill the tank with what you will burn out in a couple of weeks.