Does prop hub diameter have to match lower unit diameter?

[wire2]

I bought a ss "Turbo" prop (Precision Propeller Inc), on eBay listed as fitting a 150 Merc. I needed one for my Merc alpha gen 2 I/O. The prop hub is 3.9", the lower unit dia is 4.75"
It fits the shaft perfectly but will it operate ok in the water like that?

 

[MikDee]

Re: Does prop hub diameter have to match lower unit diameter?

Without seeing it I don't think it matters, but if it's thru the hub exhaust it maybe restricting?

 

[wire2]

Re: Does prop hub diameter have to match lower unit diameter?

Good point Mik, it is a bit smaller exhaust passage than larger prop. Still seems as large as some of the smaller areas of Y pipe & outdrive, though. I'll try to get a picture on here soon.

I have until May to decide.

 

[jimmbo]

Re: Does prop hub diameter have to match lower unit diameter?

The exhaust will be anything but restricted. Using the small hub props on a large gearcase will result in exhaust flowing thru the hub as well as over the hub. Sort of very large vent holes. If your boat is very light it could be benificial to acceleration in allowing the engine to rev up quicker. On a heavier boat it could lead to the prop slipping execssivly and never hooking up.
The 150 inline 6 used the smaller housing.

 

[Silvertip]

Re: Does prop hub diameter have to match lower unit diameter?

On a two-stroke outboard you would have "huge" ventilation issues. On a four stroke those issues remain although to a lesser degree. It may or may not be a problem.