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750hp for 1988 convincor 251??

R

rico649

Member
So I got my new checkmate convincor in last week( well old but new to me). I'm currently re-doing the floor so she can be solid once I'm ready to touch the water. My initial plan was to run twin mercury 3.0 efi 250hp engines. I was planning on taking one off of my starflite and purchasing a second one. My convicnor is an inboard version so would've had to install a bracket to mount the engines. Now I have a change of plans. I'm about to purchase a 750hp 540ci engine built by Chief Engines down in Miami. My uncle had twins in his 38' sutphen but one blew so He's selling me the other one. Before I make that move, I want to know if you guys think 750hp will be too much power for my 25'? Personally, I've never seen none with that amount of power and want to know whether it'll be practical, and also what kind of speeds should I expect if I can hold it?
 
rico649 said:
So I got my new checkmate convincor in last week( well old but new to me). I'm currently re-doing the floor so she can be solid once I'm ready to touch the water. My initial plan was to run twin mercury 3.0 efi 250hp engines. I was planning on taking one off of my starflite and purchasing a second one. My convicnor is an inboard version so would've had to install a bracket to mount the engines. Now I have a change of plans. I'm about to purchase a 750hp 540ci engine built by Chief Engines down in Miami. My uncle had twins in his 38' sutphen but one blew so He's selling me the other one. Before I make that move, I want to know if you guys think 750hp will be too much power for my 25'? Personally, I've never seen none with that amount of power and want to know whether it'll be practical, and also what kind of speeds should I expect if I can hold it?
Click to expand...

First and foremost, where are the pics of your new boat???????

Anyways my neigbor has a 500+ hp 502ci in a 19' baja and he cannot go full throttle. He essentially has exceeded what the hull can handle and it gets very unstable past 80mph and 3/4 throttle.

Now with that being said, I am sure with some K planes and a speedmaster lower unit he could probably get it more driveable, but the short version is I would be comfortable saying he has too much power.

As far as your boat goes it all depends on how fast your boat can run comfortably. Probably you are going to go way past the practical hull speed and its going to be squirrelly. With all that being said if I were in your position I can't say that I wouldn't try it anyways:D
 
Several have put big power in a 251/253

Make sure you have hydraulic external steering. Is an absolute must at that hp. Boat should respond well and with some seat time you can handle her. Will be a new learning curve for sure though.
 
Thanks for the feedback guys. I don't know how to upload images to the thread. If you can tell me how to, I will... thanks in advance
 
you would need to upload them to a photo hosting site like photobucket or something similar then attach them in the post.
 
Damn! Wish I had that problem!! 100% agree with G.F. Hydraulic steering is a must! Most likely need something more substantial than a stock bravo1. Speed... I would guess in the mid 90 range? Sammie "Viper1" & others on here would have much better insight. I have a 1988 251 as well.
 
The motor in my 259 dyno'd right at 700 and I have seen low 80s on gps. That boat is a little lighter and a little narrower from what I have read. It depends on the setup and torque curve but mid 80s shouldn't be a problem if you get it set up.
 
Motor in my 253 was 700+ (supposed to be around 750 @6300 rpm) but I never got the top end speed figured out on it due to losing power steering belts above 6000 rpm. I was easily scratching on 80 and still accelerating when that happened. Hydro steering saved my azz majorly when that happened. I'd have been in the hospital if not for that. At least if you lose hydraulics, you can hold the wheel in a straight position, can't turn it, but you can hold straight until you can pull back. Without the hydro steering the boat will rip the wheel from your hand and go into sharp right hand instant turn. Not good stuff.
 
Photos of Convincor

Just picked her up from the port.

http://s1224.photobucket.com/user/Rico649/media/Mobile%20Uploads/image_zpskksniebw.jpg.html?o=0
In back of the yard, starting surgery. Pulling the old floor to redo.
http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zpsixydsuek.jpg.html?o=5

Old floor is up

http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zpsnsmgmiuf.jpg.html?o=2

Back View

http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zpsb6zppbpz.jpg.html?o=3
Measuring new wood before it is installed and glassed

http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zpsabtymbca.jpg.html?o=1


Hopefully, the floor will be done by Friday the latest. Than I'll have to go and pull the inboard from the Sutphen and start installation by early next week.
 
in my 251 ran close to 600hp, without Hyd steering, tested a few times, pulled the engine, not safe, my 253, 700+ no issues with full dual ram steering, but at 80+ things can still go wrong in a hurry, boats can handle it if you can..
 
New Floor installed.

So, am a little bit ahead of schedule. The new floor is down and just waiting to cure properly.

http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zpsiejyjq25.jpg.html?sort=3&o=3

http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zpsccbealaw.jpg.html?sort=3&o=1

http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zpssrcai55i.jpg.html?sort=3&o=2

http://s1224.photobucket.com/user/Rico649/media/Mobile Uploads/image_zps97fmntko.jpg.html?sort=3&o=0

We used 5/8 pressure treated wood. That wood is real heavy, but I wanted to make sure that the boat is solid so I don't have to go back in the floor again. After all, I'm in the islands and will be participating in Poker runs and island hoping from time to time.
 
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