3 blade to a 4 blade prop
 

Guys,
I have a 2000 Mariah jubilee 24 deck boat 5.7 liter 2 barrow carb that I own with a friend. He would like more power for pulling heavier skiers. He thinks I should change the intake and carb to 4 barrel to get the extra power he wishes. I am a former auto/truck tech and now a trainer and am tentative with this due to previous hot rod engine issues (throwing money at something blindly can just produce more issues). The boat orginally came off the ocean at the Florida Keys and now resides in Minnesota on the Mississippi. It is rarely used except for acouple of weeks in July. All the families gather for this time and the boat is used heavily. The engine runs well back apears to have a slight stall (not quite a hestitation) when pulling a good size skier out of the water. I got it to improve last year by advancing the timing abit (timing chain looks to be in good condition). I thnk a carb rebuild will help as well (accelerator pump probably needs replacement).
However, he has always wanted some more power.. top speed is not a real concern. I am not sure if adding a 4 barrel carb will help. I have read recently on the Mercruiser site that going from a 3 blade to a 4 blade prop can help with torque out of the hole. The boat should plane faster with quicker acceleration, but you will lose some top in speed. Is this a possiblity as I have 3 blade props (see below) ? if so, how expensive i(ballpark) s it for the props? Can they be changed easily? or any other ideas as how I can improve this?
Thx for any help you can offer.

FYI: the boat has the black coating on the hull since it was in the ocean. Does this have an affect on power and can anyone suggest a way of removing it. I friend said watered down muratic acid. Seemed a bit harsh for the hull and the guy removing it.

Re: 3 blade to a 4 blade prop
 

First need to know what your WOT(wide open throttle) is at with your 22P props you have now.
You need to be in the 4400-4800 RPM range. A touch more(5000 RPM) isn't a biggie , but less is no good.:shakehead:

Check out these for giggles , but the price is spendy.:eek_animated:
Stainless Steel Propellers, Boat Props, Marine Accessories | Hill Marine

Re: 3 blade to a 4 blade prop
 

You could always read the STICKYS at the top of this forum....

Re: 3 blade to a 4 blade prop
 

I spoke with someone at iboats.com and they thought it best to just change the 3 blade pitch from 22p to 21p. Any thoughts on this? will it help?

Re: 3 blade to a 4 blade prop
 

I check the stickys on Mikey.. thx..

Re: 3 blade to a 4 blade prop
 

What is the advantage of going with 3/4 blade combo compared to a 4/4 blade combo?

Re: 3 blade to a 4 blade prop
 

No idea. Never seen a duo-prop mismatched like that.

Re: 3 blade to a 4 blade prop
 

Read Larry's post #2. You need to know you rpm's at WOT with existing props first. Any changes without that info is only guesswork.

Re: 3 blade to a 4 blade prop
 

I'm told 4500 rpm.. Will going from 3 blade to 4 blade really affect that while keeping the same pitch? I realize I'll lose some top end speed but will rpm be affected since the pitch won't be changed?

Re: 3 blade to a 4 blade prop
 

If you go from a 3 blade to a 4 blade in the same pitch you will increase your rpms probably by 150 or so. If you are accurate at 4500 then you could drop to a 20" pitch 3 blade prop which will bring you up around 4900 - 5000 at WOT but you will see a significant increase in low - mid range ooomph. Keep the 22" props for cruising or simply sell them to offset the cost of new props.

Re: 3 blade to a 4 blade prop
 

I can get my hands on 21 pitch 3 blades. Would that work better yet?

Re: 3 blade to a 4 blade prop
 

21 pitch props will work better than your 22's for what you want to do with your boat.

Re: 3 blade to a 4 blade prop
 

We got a good deal for a nice used set of 20's 3 blade installed. Since we will be running higher rpm's is there anything I should consider adding? is one of those Holley 500 cfm worth adding or just keep it the same (though I'll probably rebuild it)? it currently has a the 2 barrel rochester on the 5.7L. thx

Re: 3 blade to a 4 blade prop
 

No the prop change should be fine. Switching over to a 4bbl will only use more fuel.

Re: 3 blade to a 4 blade prop
 

I agree, I was thinking of the holley 500 cfm 2 barrell though. I think the rochester is probaly 250 - 300 cfm.

Re: 3 blade to a 4 blade prop
 

Leave it alone and go have fun!
That will work great for the "play" mode your looking for.
Just don't let her go above 5 grand , and you'll be fine.:wink_thumbup:

Re: 3 blade to a 4 blade prop
 

good point.. will do :)