Changing Gear Ratios on Bravo 3

[jrglombo]

Hey everyone. This forum never lets me down so here we go. I have a 1970 SeaRay SRV 240. Repowered last year with a 383 MPI and Bravo 3 drive from a donor boat. The RPMs were never up to par. 4300 with 22P props, 4500 with 20P props. Well I had a crack in my gear lube monitor tube and my heat failed in inside storage building….water in lower unit POW she’s toast. Cracked down the whole lower casing.

Here’s what I’m trying to accomplish I have a 2.00 Bravo 3 right now. The weight of this old boat I would like to go for the 2.2 ratio. If I’m buying a new lower, I’m considering buying the one for a 2.43. With my math a gear set of 27/32 upper mated to the new 13/24 gear set lower makes a 2.19 ratio. That way I do not need expensive upper gearing and I only need to change the lower since I’m changing it anyways. Am I considering this correctly?

 

[alldodge]

I'm scratching my hear real hard at the moment because the 383 MPI should move the boat pretty good. I would start with a compression test on the motor, and if that checks out scan motor for codes and check fuel pressure

Either that or the boat weights more then original 4400 lbs

 

[jrglombo]

Thanks. I need to get my RPM’s up and I really would like to change gear ratios as I do not believe this 2.0 drive ratio is cutting it. If I’m changing the lower already I’d like to know if my math is working out. The compression test was good, and fuel burn looked good.

 

[alldodge]

ok I'll quit scratching and just try to answer questions

"IF"
you have a 2:00 B3 drive then you should have 32/27 upper and 16/27 lower

to obtain a 2:20 or 2:43 you need a 30/23 upper
So I don't think you can get there

 

[jrglombo]

I definitely have a 2.0 Bravo. 32/27 upper that I am keeping. That mated with a 13/24 lower(purchasing a new lower with this ratio) has a final drive ratio of what? I’m getting 2.19

 

[04fxdwgi25]

Just an example, I have an OEM B3 2.20 drive w/ 28 pitch props and tops out right about 60 mph (under normal water conditions) and RPM sits right at 4600/4650 RPM at WOT on the 454 Mag

 

[nola mike]

I definitely have a 2.0 Bravo. 32/27 upper that I am keeping. That mated with a 13/24 lower(purchasing a new lower with this ratio) has a final drive ratio of what? I’m getting 2.19

I'm getting that as well