1.75:1 to 1.81:1 lower unit how much difference

[newwguy]

2003 yamaha 250 ox66 My 1.75:1 lower unit is trash and I have a nearly identical lower unit but it is one with a 1.81:1 gear ratio. has anyone made this change? How big is the difference? My current prop is already a tad too much pitch and I have trouble spinning it all the way up. I have 27 pitch prop and it works great but like I said it never gets close to the limiter. 5800 rpm or so is all I have been able to hit.

[21XDC]

You will need to go up about two more pitches to maintain similar RPMs

[newwguy]

I'm hoping that since my motor slightly struggles with my current prop that the new gear ratio will help me and if I have to have the prop reworked some thats ok too.

[JJohnSind]

We used to swap out the HPDI lower unit to the ox66 to get the lower gear ratio and turn a higher pitched prop. It works, and gains speed, but you’ll struggle a bit on the hole shot.

[newwguy]

I figured I'd lose some top end but gain on the lower end with the numerically higher gear ratio. That's how it works on a car anyway.

[JJohnSind]

It works the other way around. The lower gear allows a higher pitched prop, and that turning the same rpm’s = more speed.

[newwguy]

I'm just going to put it on and see what happens. I have nothing to lose.

[21XDC]

1.81 gears are easier to turn than 1.75.... Period.

Beware who you listen to on the internet.

[kensafishin]

What Mike Lohn says. Plus the higher gear will last longer. I have a 99 vmax with original lower unit.