Change of Propeller?

[chiln22]

I have just upgraded my 1983 Mercruiser 898(305)I/O to a 1983 350 block with all my same parts. I have a Mercruiser stern drive until with 1.5:1 ratio. I was told earlier that I would probably have to change my propeller blade after I have done this upgrade.<br /><br />I don't know anything about my current propeller other than it is a stainless steel Quicksilver with number on it as follows: 48 16314 A5 17P. I also have another black aluminum propeller that has the number: 48 78120 A40 19P on it. <br /><br />Would anyone be able to tell me if I can just stay with my current prop or will I have to change it?<br /><br />Thanks in advance...JOHN!

 

[TilliamWe]

Re: Change of Propeller?

John, the 17p means it is a 17 pitch prop.<br />the 19p means it's a 19 pitch prop.<br />You will mostlikely need to change the prop.<br />If your "old" 305 turned it's max WOT rpm with the 17 pitch prop, your 350 should turn that same prop to an even higher rpm at WOT. You don;t want to over rev the engine. So would need to change to a "larger" prop, and that 19 pitch prop is "larger" than the 17 pitch.

 

[Bondo]

Re: Change of Propeller?

Ayuh,......... I'd do Sea trials with the 19",+ See What It Does............<br /><br />After a few hours of run time,.. You'll know if you need More Pitch.........<br /><br />Keep an eye on the RPMs......

 

[chiln22]

Re: Change of Propeller?

Bondo...what should I look for while running the 19" prop to see if I need more pitch?

 

[Bondo]

Re: Change of Propeller?

1st you've got to get some Hours on it.......<br /><br />I Think there's an "Engine Break-in" thread going on around here somewhere,....... Look it Up.....<br /><br />After the Break-in,... You'll want your WOT RPMs to be in the 4400/4600rpm range.......<br /><br />If it Over-Revs tooo Easy,... Go to a Bigger Wheel..........

 

[chiln22]

Re: Change of Propeller?

Bondo... Have another question, Will the diameter of the prop make a difference? The prop with 17 pitch has a 15"diameter but the prop with 19 pitch has a 14 or 14 1/2" diameter. I use my boat heavily on skiing and pulling tubers so I want to get the most out of my new engine. Any more suggestions or should I just try out the 17" prop for now?

 

[Bondo]

Re: Change of Propeller?

Basicly,.............<br /><br />Forget about the Diameter Altogether...........<br /><br />You really don't have a choice in the matter,........<br />The Engineer that designed the Prop, took into account the Blade Style, surface area, angle, rake, pitch, diameter,+ Everything Else involved to produce the final product............<br /><br />You get to pick the Pitch, Style,+ Composition of the prop,..... Oh,.. And the # of Blades......<br /><br />If Your Case,.. Right Now,... Put the 19" on it.... I Think you're going to need More,...... But Do the Sea Trials,+ See............

 

[chiln22]

Re: Change of Propeller?

What would be a standard diameter size for my boat then?

 

[Bondo]

Re: Change of Propeller?

Originally posted by Bondo:<br /> Basicly,.............<br /><br />Forget about the Diameter Altogether...........<br /><br />You really don't have a choice in the matter,........<br /> The Engineer that designed the Prop, took into account the Blade Style, surface area, angle, rake, pitch, diameter,+ Everything Else involved to produce the final product............ <br /><br />If Your Case,.. Right Now,... Put the 19" on it.... I Think you're going to need More,...... But Do the Sea Trials,+ See............

 

[olbuddyjack]

Re: Change of Propeller?

Theres a prop selection guide in the "engine faq" section if you want some more info, but the first step is what Bondo says, go for a ride and see what your wot rpms are.