Repower Help. What ratio OD ?

W

wire knot

Petty Officer 2nd Class
Joined
Aug 24, 2006
Messages
137
Its been awhile since i've posted, But I could use some help.

I'm in the process of repwering a 1975 Mako 23. It had a V8
OMC that I gave up on 2 years ago.
Im looking at 5.7 MPI
The Hull is 3600lb(dry) and the transome has been filled.

My questions are

1: would you prefer merc or VP, why?
2: what determines the ratio of the outdrive?

Thanks
WK
 
H

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: Repower Help.

Re: Repower Help.

Howdy,


If you're going to buy new Merc and VP will be close to the same price.

If you're going to buy(scrounge) used, you find a better selection of Merc stuff out there. Go to Ebay any day of the week, and you'll find at least 3 times more Merc than VP.

Having said that, when i pulled my OMC 460 King Cobra, If I had found a BigBlock+ Volvo DPS combo, I would have bought it!

I never did...... but I did find several Mercruiser SBC/BBC Bravos I/II/III locally.


The drive ratio is usually determined by the size of the engine and the size of the boat.

Most runabout boats with a 350 cu-in V-8 use a 1.5:1 ratio..... I think there's a Mercruiser calculator out there that will further refine the suggested ratio for the engine and hull size/wt etc....


btw, that boat you have is big & heavy. I would look at minimum 300 (propshaft) HP and either a Volvo Duo-Prop or Mercruiser Bravo III.




Cheers,


Rick
 
W

wire knot

Petty Officer 2nd Class
Joined
Aug 24, 2006
Messages
137
Re: Repower Help.

Re: Repower Help.

Thanks Rick,
Im gonna buy new.
I had a chance to run the old power some, it was 225hp. So I know
the performance with that set-up. Im looking at 5.7 mpi which is
300hp. haven't made up my mind on the Bravo 1,2,3 yet.

Was hoping someone might get into some theory like, if you have
xxx ratio you'll prob need xxx prop, because you'll get xyz -mph/mpg/
hole shot, ect.

thanks
DL
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Repower Help.

Re: Repower Help.

When you buy the new engine package, it will come with the proper gear ratio in the outdrive for that engine. The prop sizes are determined by boat size, weight, hull type etc. First thing you need to know is EXACTLY what engine and drive you will be getting.
 
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