Moving from 3 Blade to Four?

Roman S

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Aug 1, 2007
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Hi, New to this forum. Having engine rebuilt after bad winterizing experience. 5.7L 350 EFI 290 HP, Alpha 1. Boat Regal 1988 233xl. The original 350 in the boat had a 14/34 x 19 Stainless prop. I was wondering whether a move to a 4 blade 14.3/4 x 15 would be comparable to 14/34 x 19 prop there now? Thanks Roman
 

Bifflefan

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Re: Moving from 3 Blade to Four?

Short answer is no.
A 15p four blade is comparable to a 16p 3 blade.
With your set up I would not go less than a 18p 4 blade, probably a 20p 4 blade will do real good.
 

Roman S

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Re: Moving from 3 Blade to Four?

Thanks for the reply. I have a follow-up. In order to get to the 18 pitch, the diameter of the prop gets smaller. Namely, instead of 14.3/4 diameter, I would be looking at something as small as a 14 inch diameter prop. Thanks again. Roman
 

Dhadley

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Re: Moving from 3 Blade to Four?

Don't worry about diameter at this point. Let's start by looking at 4 blade props made for IOs. Also, when you rebuilt / replaced the 290 did you replace it with another 290? Have you run the 21 3 blade with the new motor? If so, did the 19 put you in the upper end of the top rpm range that you need to be in?
 

Roman S

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Re: Moving from 3 Blade to Four?

Great Questions. The Old motor produced 260 HP. Obviously after being broken in and brand new. That was 22 years ago. When I ran the new engine with the 19 pitch, I felt it was slow to get on plane. It is a heavy boat. That's why I was looking for some advice on the 4 blade. A little more stern lift. I am not sure whether the 30 extra ponies make that much of a difference. I may be wrong.
Roman
 

TilliamWe

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Re: Moving from 3 Blade to Four?

I think you'll find it's actually going to be more than 30 extra horsepower. Back in 1988, Mercruiser rated their engines at the crankshaft. Today, your engine should be rated at the propshaft. (Although with it being a replacement, crate engine, it could be crank horsepower as well). So it's possible that while your old engine was really 230hp at the prop, your new one is 290 at the prop. 60hp will make a difference.
I'll bet you a nickel, if your old 260 was turning the proper WOT rpms with that 19 pitch 3 blade, you'll be able to turn a 19 pitch 4 blade, with your new 290hp 5.7.
 

jason32038

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Re: Moving from 3 Blade to Four?

If you keep the same pitch and size prop and switch to a 4 blade the max rpm will drop about 200-250 rpm but if you're having it rebuilt I would switch to a 14 3/4x19 4 blade. Smoother acceleration and less vibration.
 

Roman S

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Re: Moving from 3 Blade to Four?

Generally, I plan on going with an aluminum prop for starters and a few years. The closest I can find to the original 19 pitch is a 14.5, 14.25 diamater. These are widly avaialble. So I should not worry too much about the smaller diameter of the prop, as long as pitch is correct?
Roman
 

Roman S

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Re: Moving from 3 Blade to Four?

Went to take a look at the engine specs. It is a 350 5.7 l marine power EFI. The power rating is 325HP at the crankshaft.
ROman
 

Dhadley

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Re: Moving from 3 Blade to Four?

Good motor choice, we've had very good luck with them. When you ran the old 19 and mentioned a slow holeshot, how was the top end? What rpm did you get?
 

Roman S

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Re: Moving from 3 Blade to Four?

Thanks for the replies everyone. I cannot remember. The new motor will be put in in the spring. I will probably startout with the 19 pitch that I have now. See what the top end is like and then make a inteeligent guess as to what 4 blade will work. When I get that info, I will be here again.
Roman
 

Roman S

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Re: Moving from 3 Blade to Four?

I keep probing into this thing and it gets better. The original prop on the boat was 14.5x17, not 19 as I stated before. The boat, when loaded was always hard to get up on plane. With the new engine and 30 to 40 extra ponies, perhaps a 14.5x 18 or 19, might do the trik. It will be a start. Roman
 

TilliamWe

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Re: Moving from 3 Blade to Four?

I keep probing into this thing and it gets better. The original prop on the boat was 14.5x17, not 19 as I stated before. The boat, when loaded was always hard to get up on plane. With the new engine and 30 to 40 extra ponies, perhaps a 14.5x 18 or 19, might do the trik. It will be a start. Roman

I agree.
 

Tail_Gunner

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Re: Moving from 3 Blade to Four?

Hi, New to this forum. Having engine rebuilt after bad winterizing experience. 5.7L 350 EFI 290 HP, Alpha 1. Boat Regal 1988 233xl. The original 350 in the boat had a 14/34 x 19 Stainless prop. I was wondering whether a move to a 4 blade 14.3/4 x 15 would be comparable to 14/34 x 19 prop there now? Thanks Roman


That is a loaded statement....How was the 350 rebuilt...So do you still have FI.... diameter is not a factor

3 blades will give the highest top end speed avaible
4 blades will give you lower paning speeds and better midrange performance everyday of the week....95% of your boating should occur there.

Stilletto bay pro 11 absolutey shine in the 4 blade ss arena if your boat is under 4000 lbs
 

Robbabob

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Re: Moving from 3 Blade to Four?

Thanks for the replies everyone. I cannot remember. The new motor will be put in in the spring. I will probably startout with the 19 pitch that I have now. See what the top end is like and then make a inteeligent guess as to what 4 blade will work. When I get that info, I will be here again.
Roman

I think this is your smartest move. although everyone has given great input on what should work for you, don't spend any extra money on a prop until you know what the performance will truly be. Real data from the current 19p will yield the best prop to share with you.

Good luck!
 

Roman S

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Re: Moving from 3 Blade to Four?

You guys are fantastic. Thanks for the replies. The motor will be brand new. New gm 5.7 L base from michigan motorz. Everything else I had on the 2009 will be reused, so it will still be MPI. 325 crankshaft HP
The prop on the alpha 1 now is a 17 pitch, not 19. I was originally wrong. The boat is a Regal 233xl. It is heavy. With only me aboard, it will place nicely, though slowly. Put on a few other people on board and it can take some time to get up. I am not sure what to do with 40 extra ponies or so. But I will start with a 4 blade 17 pitch. I can move to 19 pitch if needed. I will keep the 17 as a spare.
I don't race the boat, it is for midrange cruising. And, I generally have it well loaded with people, within weight limits of course.
The original prop with the 260hp Merc when brand new 22 years ago was a SS 17 pitch prop.

One more thing. When I was looking for the size of the original prop on this boat motor combination, crazycharlie had a boat like mine. He could not get good planning with the original combo. He put a 16x14 prop on his to grab more water.
Thanks again Roman
 

Dhadley

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Re: Moving from 3 Blade to Four?

At this point we're not concerned a lot with holeshot. We need to know what the top rpm is with the prop that you have, that's our baseline. From your last post we're a bit confused. Have you run the new motor or not?
 

fossill

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Re: Moving from 3 Blade to Four?

Forget the 4 blade. Get a Merc Hi Five and you'll never look back.
 

Robbabob

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Re: Moving from 3 Blade to Four?

You guys are fantastic. Thanks for the replies. The motor will be brand new. New gm 5.7 L base from michigan motorz. Everything else I had on the 2009 will be reused, so it will still be MPI. 325 crankshaft HP
The prop on the alpha 1 now is a 17 pitch, not 19. I was originally wrong. The boat is a Regal 233xl. It is heavy. With only me aboard, it will place nicely, though slowly. Put on a few other people on board and it can take some time to get up. I am not sure what to do with 40 extra ponies or so. But I will start with a 4 blade 17 pitch. I can move to 19 pitch if needed. I will keep the 17 as a spare.
I don't race the boat, it is for midrange cruising. And, I generally have it well loaded with people, within weight limits of course.
The original prop with the 260hp Merc when brand new 22 years ago was a SS 17 pitch prop.

One more thing. When I was looking for the size of the original prop on this boat motor combination, crazycharlie had a boat like mine. He could not get good planning with the original combo. He put a 16x14 prop on his to grab more water.
Thanks again Roman

Baseline prop/engine setups are designed to prevent the over rev, thus hole-shot tends to be lacking.

With regards to your prop selection, you'll be fine having a smaller pitch and watching rpm levels. Primary concern would be to have too much pitch and cause a lot of strain on the motor. It sounds like you're not in that area at all.

Hope we get a follow up early next season!

:cool:
 
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