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Diffuser ring removal

Old 09-16-2021, 06:17 PM
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Default Diffuser ring removal

Looking for advice from those who know more than I about a prop mod. Boat is an '87 Baja Sport 220. 330hp 454 and a 1.5:1 Bravo outdrive that's been raised 2". Thru transom exhaust. Distance from bottom of boat to prop CL is 6". I've got a 24 pitch Bravo on it that is box stock. Over all it does really good running 66-67mph (yes GPS) at 4600rpm. Handles well but doesn't want much trim. Trim up just a little for max speed. Any more doesn't help at all. There's no noticeable change in the boat angle when trimming up.
So I'm considering cutting the diffuser off about 5/8". Thought is to kill some of the stern lift and gain a little bow lift (of which it has very little right now). Managing a machine shop I have the equipment to do it easily.
Am I on the right track?
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Old 09-17-2021, 10:43 AM
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You will gain bow lift for sure but not sure what you will lose planing. I had a bravo built by bblades and I asked for max bow lift. He had removed the diffuser as well as added cup and it really lifted the bow.
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Old 09-17-2021, 12:23 PM
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I would try a 25 Mirage Plus
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Old 09-17-2021, 04:34 PM
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Smokediver, It planes really easy. Plus we just cruise for the most part. I go out by myself once in a while to run the snot out of it.

Griff, I'd like to try a 25 Mirage. The coin ain't there right now for buying another prop. Some where, possibly on this site, I read about the diffuser ring removal sometimes being beneficial. So thought it might be worth trying.
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Old 09-17-2021, 06:45 PM
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Well...assuming your tach is right and your prop hasn't had some work done to it...you're already running at over 95% efficiency, e.g. only 5% prop slip, which is...remarkable. My Baja 208 ran similar speeds but was 400 rpm or more higher. The hulls ARE pretty efficient...but the way you have it all hooked up, I'd be hesitant to mess with it!



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Old 09-17-2021, 10:58 PM
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Originally Posted by Smitty275 View Post
Smokediver, It planes really easy. Plus we just cruise for the most part. I go out by myself once in a while to run the snot out of it.

Griff, I'd like to try a 25 Mirage. The coin ain't there right now for buying another prop. Some where, possibly on this site, I read about the diffuser ring removal sometimes being beneficial. So thought it might be worth trying.
What if removing the diffuser ends up sucking ?
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Old 09-17-2021, 11:00 PM
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Originally Posted by bajaman View Post
Well...assuming your tach is right and your prop hasn't had some work done to it...you're already running at over 95% efficiency, e.g. only 5% prop slip, which is...remarkable. My Baja 208 ran similar speeds but was 400 rpm or more higher. The hulls ARE pretty efficient...but the way you have it all hooked up, I'd be hesitant to mess with it!
what happens if you put 23 into the equation as many say Bravo props are typically 1 less than stated.
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Old 09-18-2021, 06:56 AM
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Originally Posted by SB View Post
what happens if you put 23 into the equation as many say Bravo props are typically 1 less than stated.
Would be 1% prop slip...keeping the 66 mph as a constant.


My guess is that the tach is off a bit and the engine is actually running a higher rpm. GPS doesn't lie and we know a TEN percent prop slip is much more realistic, as a minimum:



I had never heard about diffuser ring mods so this is a great thread!

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Old 09-18-2021, 07:24 AM
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Default 25 Mirage

Originally Posted by Smitty275 View Post
Smokediver, It planes really easy. Plus we just cruise for the most part. I go out by myself once in a while to run the snot out of it.

Griff, I'd like to try a 25 Mirage. The coin ain't there right now for buying another prop. Some where, possibly on this site, I read about the diffuser ring removal sometimes being beneficial. So thought it might be worth trying.
Not sure where you are located, but Cool Breeze at LOTO, may have one you can try. They are very easy to work with.
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Old 09-18-2021, 07:26 AM
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It might be a little harder to get on plane if you remove the ring,I would look for one with the ring already removed so at least you have your stock one to fall back on.
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