Right prop for mismatched engine combo?

[Darkhorse1201]

I have a 1992 Sunbird 18' with a 4.3 V6 OMC and a 5.0 outdrive (I verified this with the numbers). I just bought the boat and it did not come with a prop. What size and pitch should I be looking for? I beleive the 4.3 came with 14.25" x 19. Should I pitch up, down or stay the same due to the different ratio in the 5.0 outdrive? Thanks in advance

 

[Haut Medoc]

Re: Right prop for mismatched engine combo?

I would run it with what you have & see what your WOT is as opposed what it should be.....You are gonna have to go down in pitch, I would think....With the wrong gear ratio, you may never get it quite right....Trial & error on this one....Good Luck!

 

[Richard Petersen]

Re: Right prop for mismatched engine combo?

18.5' bowrider with 5.0 L 220 hp, perfect on 14.25 X 21 X 3 blade Alum.=56 GPS. 4900 rpm-limiter on.

 

[jtexas]

Re: Right prop for mismatched engine combo?

jk, what he has is no prop...I predict it'll overrev... sorry just couldn't resist. <br /><br />to mathematically adjust for the new outdrive, old gear ratio divided by new gear ratio times the old prop size equals new prop size.<br /><br />That would give you a higher pitch if the ratio is higher (prop turning slower at same RPM) and vice versa.<br /><br />I'm no expert, this is just a theoretical reference point. There's also weight difference and other prop characteristics...<br /><br />good luck & have fun!

 

[Darkhorse1201]

Re: Right prop for mismatched engine combo?

4.3 ratio is 1.68 and 5.0 is 1.57 - at least thats what I was told on another forum. I guessing that a 14.5" x 19 would be my best bet. (based on the learned opinions from this site.)

 

[Haut Medoc]

Re: Right prop for mismatched engine combo?

Jtexas, missed that! Thought he said he had 14 x 19....swsidlo.....That sounds like a good place to start....JK

 

[stevens]

Re: Right prop for mismatched engine combo?

"swsidlo" ????<br /><br />Edit: Never mind - I see it now. For a minute I thought it was some internet acronym that had passed me by. Like it took me a while to decipher "ROFLMAO"....

 

[Darkhorse1201]

Re: Right prop for mismatched engine combo?

Thanks everybody - Does anyone know how to figure final gear ratio? P.S.by the way WHAT does ROFLMAO mean?

 

[Haut Medoc]

Re: Right prop for mismatched engine combo?

Rolling on the floor laughing my a$$ off.....Can't help with the gear ratios, sorry....JK

 

[vipzach]

Re: Right prop for mismatched engine combo?

If that v6 came with enough power, say around 200, the v8 drive ratio may work just fine!? I think a 14x19 would be a good place to start. Just keep an eye on those rpm's.<br /><br />Go to some local prop shops and see if they will let you "try before you buy" Let them know what you have and that you have every entention to buy a prop, just don't know which one.

 

[Bondo]

Re: Right prop for mismatched engine combo?

4.3 ratio is 1.68 and 5.0 is 1.57 -

That's About 4/5"s of Prop Pitch,........<br /><br />If the 4.3l ran a 19" prop with the 1.68/1 ratio,................<br />You're going to Need a 15" or Smaller Pitch to run the 1.57/1 ratio drive................

 

[Darkhorse1201]

Re: Right prop for mismatched engine combo?

I just checked and I got the ratios backwards. The 4.3 ran 1.57 ratio and the 5.0 ran a 1.68. I guess I will have to buy a couple of props in those ranges outlined above and experiment until I get the RPMs close. Thanks