Prop Question....

I have a 92 18ft champion powered by a 92 Mariner Efi 175hp with a 25p tempest without a jackplate...I bought the boat like this and prop has been on for awhile without any damage in the engine. The question is if it too much prop for that setup. The reason i ask is because my mechanic says it needs about a 23p for optimal performance. The tach is currently not working but when it did it ran about 5100-5300rpms WOT depending on the load with around 56-60mph depending on load also. I get a pretty good hull shot and i guess good top end. I don't know much about the engine and don't want to damage it by too much prop. My mechanic is a certified mercury tech. What do y'all think?

I wouldn't change anything until you get a working tach so you can see what it's turning @WOT.

I am pretty sure WOT on that motor should be 5500 rpm. Your prop pitch can be dropped 1" by a prop chop which will increase rpm by about 200 rpm....this will also improve hole shot...

your mechanic is right. that efi needs to run 5800ish.

now.. if you are gonna put a jack plate on it. i'd go with a 6" and run the boat again
after you get the tach fixed.. then see what the rpms do. they will go up.. but your
"setup" will be better with proper setback and the correct height.
then fine tune your prop with new numbers.

Solid advice right there.