Propeller selection info and speeds

Big Block Power
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Re: Propeller selection info and speeds

Post by Big Block Power » Wed Jun 08, 2016 9:18 pm

Yes that's a bit high. I'll check down here maybe can do some 2 day shipping and be cheaper? Do you have a prop shop around. They Normally have a good selection of new and used. Sorry do youth have the SX drive?
I just searched some cl and in Pittsburgh there is a prop and philly has a new 4 blade aluminum 19 for cheap. Worth a try even. Good spare even. He said he will ship anywhere in the usa.
Last edited by Big Block Power on Wed Jun 08, 2016 9:42 pm, edited 2 times in total.
2003 Cobalt 220 8.1gxi
Neenah Wi

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liquid
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Re: Propeller selection info and speeds

Post by liquid » Wed Jun 08, 2016 9:34 pm

There are a plenty of marinas and repair shops and a west marine. I just don't know the inventory or who carries what or even exactly what i want...

I was going to get a 4 blade SS - but that was based on figuring out what pitch I wanted to get to and doing what I do - ridiculous research. I wanted to have a back up prop in case I do something to the new one - but I didn't want to buy a new version of the prop I already have and have that end up being the back up prop. That's stupid, and probably what I have to do at this point. If i have to pay 200 for a prop that I don't need to think about until next spring than so be it. Just wish I knew exactly the prop I wanted now.

Thinking of moving down from a 21 to a 19 when i switch to the 4 banger but i haven't tested at WOT to have enough empirical knowledge.

I'm going to ask my dealer tomorrow for either a loaner for the week or a demo and see what they have laying around. They aim to please so it shouldn't an issue and buy some time to do research.

yes it's an SX RH
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5.0L Volvo Penta GL

Big Block Power
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Re: Propeller selection info and speeds

Post by Big Block Power » Wed Jun 08, 2016 9:46 pm

Look at my thread above yours again I added to it.. Yes I think 19 four blade will work. The issue is the diameter and cupping changes the rpms so much. Yea a test prop would be great for you. I wish there were others here that had the same set up as you but we know that's not the case.
The ss is a 19 three blade and a bit higher than I first thought.
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Re: Propeller selection info and speeds

Post by liquid » Thu Jun 09, 2016 1:35 pm

That 4 blade looks perfect... price is right to try!

How do i find the listing?
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Re: Propeller selection info and speeds

Post by Big Block Power » Thu Jun 09, 2016 7:40 pm

I'm sorry it didn't pop up there was a new posting. Just search Pittsburgh craigslist for Volvo prop it will pop up.
Yea the price is right even if it didn't work perfect but it should be a bit better than what you have and a good spare.
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Re: Propeller selection info and speeds

Post by liquid » Fri Jun 10, 2016 10:42 pm

BB you are a scholar and a gentlemen - I appreciate your helping me out. I spoke to Thomas who was slinging those props. Nice guy and very honest.

It was the wrong pitch.

If i'm running the correct prop (which I am. Spoke to Cobalt about that) then adding a blade will add RPM's obviously. Dropping from 21 to 19 will also add RPM's... so if I do both of these I could very well be exceeding my RPM's if i hammer it. Now i don't worry about me but I do worry about someone else not knowing the limitations of my boat. While I don't often let other people drive there is one that would concern me.

So... i bought the exact same prop - volvo 14.25 x 21 new. Spoke to the techs at my marina and had my old prop shaved down cleanly. Then I left... and kept thinking... which I do incessantly. So I called on my way home with my new prop and old prop in hand and discussed the 4 banger.

They told me to put the new one on and run WOT and report back data - they would take the prop back and order the 4 blades based on my report.

I told them to order the 4 - 14 x 21 as I had already worked out my range and to confirm my thought process with volvo and cobalt.

Just as i was about to put the new prop on the tech called me and said leave it in the box. He's sending me the 4 banger. My assumptions (should be) correct. Adding the blade should add 2-300 RPM which should keep me right in my 4400 - 4800 range. I'm running the cleaned old prop gently this week on vacation.

If you read any of my posts you'll know I do 9/10's of the work beforehand. I think I'll be right where i want to be.

Sidenote - If i say "prop" anywhere near my pregnant wife in the next 10 days she might lose her mind.

Any way. thanks for your help, it's comforting to know there are other lunatics out there.
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Big Block Power
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Re: Propeller selection info and speeds

Post by Big Block Power » Sat Jun 11, 2016 9:32 am

I'm not sure why they said adding a blade will add 200-300 rpm? It may drop that many rpm. I ran a 17p rev 4 a 19p high five a 21p vensura 4 blade a 21p vengeance on my crownline. All stainless.350 mag all ran about 5000-5200rpm max was 5200 on that engine. I have no idea what a aluminum would ruin I would say prob a 21or23p. Of course cupping and diameter makes a huge difference. The way I look at it your adding a blade which is more resistance in the water which in turn will slow the engine down. Well let's see what yours will do when you get it on and what wot wewill be. Glad you got something for this weekend though.
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Re: Propeller selection info and speeds

Post by liquid » Mon Jun 20, 2016 12:05 pm

Vacation was quality - will post pics soon...

Wanted to just add that adding a prop WILL lose RPM's not add like I said in my last post... I was rushing to post that but you're exactly right BB.

Hopefully if I'm in my range of 44 - 4800 and i lose a few hundo I should be right in my sweet spot... Only one way to find out and that's to slap it on.

I'm traveling this weekend so I won't get a chance to try her out for another few weeks. Will update when I can.
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Re: Propeller selection info and speeds

Post by Big Block Power » Mon Jun 20, 2016 6:23 pm

Keep us posted. Can't wait to hear results. I would like to see 4800.
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Re: Propeller selection info and speeds

Post by liquid » Tue Jun 21, 2016 1:36 pm

so more tinkering here folks!

emailed Ken at Prop Gods - if you've poked around on the hull truth or other sites you know his word is pretty much gospel....

Here's his reply:

The prop I like for 4 blades on that setup would be a Powertech SFS4.
Pulls well, still fast on top end.

Pitch will depend on your gear ratio. Should be stamped on a little plate on the side of your outdrive. I think its 1.60 but take a look.

If its 1.60 and your getting 50 MPH on GPS, then I'd go with a 19 pitch.

If that speed is from speedometer, then I'd double check it with a GPS or get a speedometer app on your phone. The gauge in the boats are notoriously inaccurate.

The ultimate acceleration prop for water sports is the Quicksilver QST5.
Docking is not that great, but the holeshot and ability to stay on plane at slower speeds is impressive.

...

If anyone wants his info PM me - I don't want to post it.

So now my question is - Keep the three blade that Cobalt recommends for my rig (14.25 x 21 x 3) and get the Powertech SFS4 as a CHristmas present to myself... Do i exchange the 3 blade for the 4 at my dealer (14 x 21 x 4) that i (now) think is not the ideal pitch and give it a try... Or do I have my dealer order the (14 x 19 x 4) Volvo prop and exchange that for the one I have on there right now?
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