4.3 to 5.7

There are limits to what you can increase in pitch before it becomes inefficient. What is the pitch now?

 

19

 

To maintain the same ratio, the pitch should be a bit over 23". Extreme pitched propellers are good for very light boats at high speed. However, they are really poor for initial acceleration.

 

So according to that chart, higher horse power engine has a lower gear ratio?

 

So I get some of the accessory drive parts in today and moto should be here tomorrow

 

That is correct.

 

Those are mercruiser, do it's the same for volvo penta?

 

Yes, it is the same principle for all engine/propeller matchings, no matter what label colour. It is because the power absorbed by the propeller is primarily depending on the rpm's it is rotating with. A 15" propeller coupled to a 130 hp engine will have to rotate slower than the same screw coupled to a 300 hp engine. Now, if the engines produce max power at about the same rpms, the gearing has to be different. The prop does not know what is turning the shaft, only that it has to rotate at a certain speed to transmit a given power input.

You can use the following rule of thumb for a rough preliminary estimation of diameter or shaft speed : D = 630 * P^0.2/N^0.6;
Here D: diameter in inches, P: power in HP, N: prop shaft speed in rev's/minute.

 

Now you give me alot of mathematics to do but I get your point. All of what i'm throwing at this crate moto it's going to have alot of power.. Holley EFI with timing control enabled.. but I don't think will able to get that gear ratio swap anywhere around here in Maine, cause there isn't much here..

 

What model and year OMC do you have?

 

1996 volvo penta sx colbra

 

If you have a joint venture era drive, it will be interchangeable with other volvo penta parts. You can change the gear ratios on the top, bottom or both.

 

I don't, I wonder how it would cost for a set of gears

 

Volvo Penta gears are expensive and you need a complete set of tools to install and set them up properly. You will be better off to try to trade it in for an outdrive with correct gears.

 

Oh I see