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???'s about outdrive final ratio

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???'s about outdrive final ratio

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Old 05-06-2014, 02:38 PM
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Default ???'s about outdrive final ratio

So as I was surfing here last week I stumbled across the Bmax drives a member has for sale in SS forum and I started thinking about the fact I didn't refresh or repower this winter as I'd hoped to.
I've always tried to be proactive rather than reactive and am strongly considering buying stronger drives before the engines get redone or replaced.
I understand that 1.30 vs 1.50 requires downsizing pitch. My buddy told me 1.30 final drives were for lower rpm diesels and the info I've seen on threads also refers to smaller pitch on equal power.
What I'd like to know is that is there a specific formula for hp/torque increase that would offset the need for changing pitch, kind of like the amount of extra hp it takes on each side to gain 1mph
If after upping power accordingly do y'all think that the same pitch (26) with a 5 blade prop instead of 4 blade would place undue strain on the old style B-max drives. My understanding is that 1.30 is harder on a drive than 1.50 just as a 5 blade is harder on the drive than a 4 blade so this could essentially be twice as hard on a drive.
And one last question for you guys. How much would y'all feel that a pair of new style B1 sweptbacks in excellent condition with 80 hrs, oil changed twice with bravo shop synthetic would be worth.
I bought them a couple of years ago because I thought I'd be taking my old ones to the limit with the new power I didn't install this winter.
I paid 6k for the pair when I purchased them.

Thanks for any insight,
Kelly
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Old 05-07-2014, 01:28 AM
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There is no difference in strength with different ratio Bmax drives.

You would probably need to add about 150hp per engine to keep the same props at the same rpm going from a 1.50 to a 1.30.
If you go to 5 blade instead of a 4 blade, you need to drop 2-3 of pitch.

You used Bravos' would probably be worth around 2k each.
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Old 05-07-2014, 12:36 PM
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I guess I learn something new everyday cause I didn't know that you also drop pitch when going up one blade
My understanding is with 5 you get better cruise and come up easier.
When I bought those drives I thought they might have been worth less but they were so clean I looked past the price. The guys shop, boat, and eveything he had within was spotless. I could just tell he took pride in taking care of his stuff.
Griff, thanks for your input
See ya,
Kelly
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Old 05-07-2014, 12:56 PM
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Originally Posted by huskyrider View Post
I guess I learn something new everyday cause I didn't know that you also drop pitch when going up one blade
My understanding is with 5 you get better cruise and come up easier.
When I bought those drives I thought they might have been worth less but they were so clean I looked past the price. The guys shop, boat, and eveything he had within was spotless. I could just tell he took pride in taking care of his stuff.
Griff, thanks for your input
See ya,
Kelly
Really depends on the prop Kelly.

A 4 blade bravo is considered 1 pitch number too high by most prop shops, ei; a 32 4 blade is really a 31.

Now go to a five blade Maximus and the diameter goes up from 15.25 to 15.75 and they are considered heavy on the pitch side maybe a 32 is considered a 33+ with that prop. Most lab these back down to 15.25 for performance boats

However, most adding blades are trying to reduce slip, so losing a few rpms up top can actually increase top speed and mid range running the same pitch as before. If you have a high x or high hp you usually don't go down in pitch. If you have deep legs on a big heavy straight bottom boat you will need to drop pitch to turn the 5-6 blades effectively.
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Old 05-07-2014, 01:34 PM
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I'd guess that I fall in the deep leg flat bottom group as my current and the ones I purchased certainly appear factory depth. They don't look like shorty lowers.
Do y'all know if my extension boxes change the elevation of the prop relative to the boat like the shorties do or does it remain the same.
The props are way back in the swim zone behind my molded to the hull swim platform and not beneath it like I see on pics of other 38 specials where they are completely protected from above if a swimmer jumped straight down into the water.
As always, thank you guys for all your input.
I pick up more valued info every time y'all assist me.
See ya,
Kelly
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