Mercruiser 165 (4.1 L6) Prop Pitch question

[998cc]

All. I am continuing with my 1972 Gulfstream project and would like the benefit of your experience here. I understand the relationship of pitch to speed versus power but do not know the relationship of pitch and diameter as they relate to my specific needs. Looking online, finding this info, especially for a 40-odd year old drive has been a challenge.

What I want to end up with is a boat that I can use for both fishing and water-ski/wake boarding. For trolling, I'll use a trolling motor. Top speed is not a concern as long as the boat will pull a skier and plane. The black aluminum prop on the boat has seen better days and is unmarked for pitch/dia as far as I can tell. I do have a second outdrive with a nice stainless prop with a pitch/dia of 12-3/4 X21. Does this sound like a prop that will get me into the realm?

Thanks.

Russ

 

[airshot]

Re: Mercruiser 165 (4.1 L6) Prop Pitch question

Need alot more info....boat size, weight, tach readings at wot etc.

 

[998cc]

Re: Mercruiser 165 (4.1 L6) Prop Pitch question

You're right; after giving it more thought, a lot more info is definitely necessary to nail it down. It's an 18 foot, V-hull, closed bow, 6 seater. A pretty standard 1970's ski boat. Weight is unknown, and I have never had it in the water, so WOT and tach readings are not available. Perhaps the best approach will be to just wait until I get the outdrive done, get'er in the water and see what she does with the stainless prop installed.

Thanks
Russ

 

[jestor68]

Re: Mercruiser 165 (4.1 L6) Prop Pitch question

Here is some basic info to work from.

The Mercruiser 165 is a 3.7 Liter in line 6 cylinder motor. Like new compression is about 150 psi. The standard gear ratio would be 1.7. Spline count is 15. Recommended full throttle rpm range is 4000-4600 rpm.

The 21 pitch should get you within the rpm range, although I suspect a 15 X 19 pitch would work better for your stated application.

 

[998cc]

Re: Mercruiser 165 (4.1 L6) Prop Pitch question

The 21 pitch should get you within the rpm range, although I suspect a 15 X 19 pitch would work better for your stated application.

So, to get my bearings here, is the 15X19 a higher or lower "ratio" so to speak? Will it result in more power or more speed per any given RPM than the 12-3/4X21? I sense that the 15X19 will result in more power, less speed. (which is likely a good thing for my needs)

Thanks!