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251 Convincor Cummins Diesel

And in theory I should almost be heavier in the water than the 502. Not much by the time water manifolds etc, but I still think heavier. It seems like with the 502 the prop would've spent more time out of the water than in. Bare with me, I'm learning
 
Problem Child said:
Cool thread . I just really want to see it roll coal right in front of the water nazi:s. I could have swore the Superboat runs 92. hmmmm.
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Lol. According to my wife it doesn't.. the fact is she's only been 86 in it. So I guess she's right

She started out a bit scared of the speed and I wanted her to feel comfortable with it so I've been pretty conservative with tabs- but now she's talked enough trash over this past winter guess I'll raise em on up. :thumb:
 
osr1 said:
And in theory I should almost be heavier in the water than the 502. Not much by the time water manifolds etc, but I still think heavier. It seems like with the 502 the prop would've spent more time out of the water than in. Bare with me, I'm learning
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My guess is that maybe with the 1.5:1 ratio, you aren't spinning the prop fast enough for it to really work properly. I know if I was only spinning my gas motor to 3900 or so and tried trimming up, my boat would fall flat on its face. I'm thinking you need to get that ratio down closer to 1:1 somehow. Then you would be spinning your prop as fast if not faster than the gas motor guys.

By the way, very cool project!!!! I love seeing something different!!
 
Well, Due to delays with the machine shop It looks like I only get to play with one diesel toy this year. The plus side is, that is the boat, and I can use the budget for both on it. Can we talk about what drives are out there that could grow with what I'm doing as far as prop options and gear ratio changes? I really dont wish to move the motor ahead to put a transmission behind it as I would loose my back seat.
 
osr1 said:
Well, Due to delays with the machine shop It looks like I only get to play with one diesel toy this year. The plus side is, that is the boat, and I can use the budget for both on it. Can we talk about what drives are out there that could grow with what I'm doing as far as prop options and gear ratio changes? I really dont wish to move the motor ahead to put a transmission behind it as I would loose my back seat.
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I would say with diesel and all the torque and a bravo based shiftable drive would be an IMCO SCX or a Bmax from The Bravo Shop. Both are around similar price range and can be equipped with multiple gear ratios. The Bmax will bolt right where the bravo does and the Imco will after changing the drive helmet. Downside, they both cost around 14 grand new. Used ones are hard to come by except for the older version Bmax that had issues.

If those are too spendy, trying to find a Bravo x diesel drive would be your next best bet but won't handle much power over a fairly mild cummins. You could also have your drive built to x/xz/xr specs with a lower ratio. All depends on your budget really.

Ultimate drive replacement would be an Arneson, but that's ~24k for the bravo replacement kit.
 
I do want to save some money for finishing the interior etc. Doing some research before joining here I did hear the term XR a few times. People mentioning that in larger crafts where 2 cummins were used to repower, that was the drive being used. I will try and learn more about that. 25k is out of the question for this project. I'd like to keep the drive budget to 5k. However if I wont be happy with the end result then if it has to 14k it has to be 14k. That just wont happen right away. Thank you for the info as always.
 
I would say a cheap route to go, just to see if you heading in the right direction, would be to find a 1.36:1 Bravo drive. You can pick one of those up pretty cheap. Throw it on there and see if dropping the ratio helped any. It might not get you exactly where you want to be, but you would know if you headed the right way.

Also, try giving The Bravo Shop a call and see what they say. They might have some other options for ya.

http://www.bravoshop.net


You might be cheaper to put an extension box on your boat and use that to house a transmission that way you don't have to move your engine forward and could keep your back seat. I know that's what Bill did on his 300 Convincor with the #6 drive.

If you find out what you need and are on Facebook, contact a guy named Mike Mello. He has a warehouse full of used parts and everybody that deals with him has been very happy. I know I bought a Whipple off of him for my Dad's boat and he was awesome to deal with. He might have, or be able to track down what you would need and it would be used saving you some $$$$$.
 
Also, PM Mr. Gadget aka Dick Tryce on here. He is a great guy in MI that builds good upgraded bravo drives. He could change the ratio of your existing drive and upgrade your current case to an XR with steel tower for much less than your stated drive budget probably. He is who will upgrade my drive when I manage to scrape up the funds.
 
It's still high for the budget, but, I did (oddly) find a "New" Bmax close to me. There are a few downsides though, It's older (2010 although new) so I'm not sure if thats one to avoid because of the mention of problems with certain ones. Also on the down side it's a 1.5 ratio and it's a shorty so I'd need to see if gear can be changed, and get a spacer. It is Half the price of a new one though. I talked to the BravoShop (before I knew of this drive) and John took the time to talk with me and of course suggested a numerically lower ratio such as a 1.2:1 or even a 1.1:1 he said. Would be a sweet setup for me if only the gears and maybe a spacer had to ship from so far away.
Still though the money is going to get up there I'm sure anyway. Thats assuming I can have just anyone (reputable shop local maybe) do the gear swap. Sorry to ramble just looking at all avenues.
 
It can be trimmed all the way down because it's too far ahead on the trailer. But this kind of shows it with the lower on.
image_13.jpgimage_12.jpg
 
Have you tried expierementing with different props yet? I would try different props before I tried expierementing with thousands of dollars in drives.I would recommend trying a Bravo One 4 blade in the 30-32P range. They bite great and don't blow out from ventilation. Great project! Where do you boat at?
 
The drive height is right where it should be imo.

Your problem is propshaft rpm- higher pitch wont work because high performance props are designed to work on engines that spin high rpms.
For example a 30p is designed to run at arguably +80mph with the propshaft spinning around 4000 rpms. Your propshaft is spinning more like 2500rpms and not reaching its efficient range.
Bow lift, hull drag, Hull speed vs Prop rpms, are all factors, and everything has to "match" to perform right.

you could put a 40" pitch on your boat and it still wouldnt work.

The 1.36 bravo would likely help the situation but not solve it.
 
not to mention the nose cone on that drive is not helping at all...not that much will short of massive $$$$$$$$
 
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