toyo321

I have been doing a ton of reading and I have a concern about my current project. I am upgrading HP in my boat, "24 ft." from the stock 330hp 7.4 to 650HP 509 setup. I have swapped out everything, Transom assembly to a HP and Bravo XS drive, also Imco full hydraulic steering to the helm, manual trim indicators and a ton of other engine compartment changes.

I know that when any boat manufacturer originally designs a boat they do it around a certain power and drive combo so they have a X dimension based on that stock factory package and in my case it was a 23p Mirage Plus. But my concern is that everyone I have talked to says that when I make this jump to 650HP I have to use a 4 blade prop or I will be blowing out everywhere. I bought two Bravo 1 props from a OSO member a stock 28 and a 30 to start with and I have heard that in order for these props to run effectively the X dimension on the boat needs to be shortened to optimize these props.

Has any one with the same type of project have any good advice about what to expect when when making this type of change in power and in props , and what happened when they did their upgrade.

The thing is I know all prop's do things differently with certain traits to different hulls. Does any one have any relative experience when they repowered their boat HP by a factor of 2 and what happened after they did their upgrade.

I know there is going to be a lot of seat time to get it dialed in but any advice would be of great help.

the deep

iTrader: (8)

I went through a similar process a while back with a 1988 FourWinns 210 Horizon powered by a sbc 350ci . I built a very stout 383ci and installed with CMI polished headers and dry tails . At wfo you could not turn the boat and the slightest ripple would start a nasty chine walk . The following winter i dismantled everything and reglassed the the transom . I raised the x by 1 7/8 " . A ton of work but a big payoff . The boat handled like a dream and had a radared speed of 68mph . This speed run was in very rough conditions with wifey screaming so i like to think there was a little more there . Still a very fast FourWinns open bow . A friend of mine added a procharger to his Crownline 454ci mag and the same problem with steering and chine walking . He installed a -2" Imco and Bravo I prop done by Cutting Edge Propellers and most of the problems disappeared although it will still torque roll to the left . Over powered hull me thinks . Anyway yes , a shortened drive or raised x dimension will cure some ills caused by bigger power . Bravo I prop will give you bite but unless tuned by a pro will give stern lift issues . This is probably my longest post to date , i'm usually short and to the point .

toyo321

So if the torque roll is going to be an issue I guess I am going have to invest in some K Planes. I was hopping that I could wait but I would rather get it done now than hit the water and then be SOL because I didn't do it over the winter. Better to have all the right stuff in place to now that the engine is out of the boat.

the deep

iTrader: (8)

I couldn't say if that will be an issue for you , every hull is different . Someone here will probably know the answer to that question .
" There is nothing half so much worth doing as simply messing about in boats " K. Grahame

the deep

iTrader: (8)

This may be of interest to you . Similar boat . http://www.offshoreonly.com/forums/g...0hp-worth.html

professor_speed

http://www.offshoreonly.com/forums/g...va-spyder.html

I would pm some of the guys here and see what worked for them

toyo321

I have combed these forums for everything with my Boat. I wish I could have contacted KidNova. He was close to what I have done but I am definitely over his 502 install.

Like I said I will wait to get it in the water and see what happens. Like I said I will have to put in the seat time to find out what tweaking will need to be done.