Drive ratio
 

Trying to decide what outdrive gear ratio to go with after my upcoming engine swap...

The boat is a Velocity 290sc.. Currently has a 496 Mag HO and a 1.5 ratio Bravo X ..

Running a Hydromotive P5X 25p, fastest I've seen has been 69.9 MPH..

Others with the same hull / power have reported 72 mph with a labbed Bravo 28....

My new engine dyno'd at 1020 HP @6000 RPM in full marine dress..

So, using a boat speed calculator using 72 mph at 425 horse puts me at 110 mph with 1020 hp..
(which seems close as I know of another 290sc with 750 ish hp that runs 94 mph ...)


SO, that being said, figuring on about 11% slip, a 33 pitch (Bravo 34 ?) prop would theoretically put my boat at 110 mph at 6000 RPM with a 1.5 ratio drive..
OR 29 pitch (Bravo 30 ?) with a 1.30 gear ratio..


Which one would you go with ?

I've come across a few used Bmax drives & Imco SCx's with the 1.3 ratio..
haven't come across any used with the 1.5 ratio yet, but may be able to swing a new one once I get my other boat sold..

THANKS !

Doug

Personally I would stay far away from the SCX, at least take a really close look at the lower housing and imagine how it will go through the water.

Sounds like a few ifs here. If you can turn a 34 prop up to 6000 rpm would be the first.

Not sure what you are saying?? I lost a Little speed BUT 4 summers now and NO DRIVE LOSS- Compared to usually 2 drives a Summer-- U add it up. I have only about 750 HP.

I think you can put XR lowers on it if you prefer. I didn't. I prefer to USE my boat lol

I'm saying from my personal experience I would stay away from the SCX.

I would likely use the "SC" lower with it if I got an SCX.. Most don't seem to loose much speed with this combo..

However, I've found better deals on 1.30 ratio Bmax's.. just don't know how the ratio change will affect overall performance.. :)

What about the new SCX blueprinted lower? Looks like its more efficient than an XR by a mile.

I ran a 280 with 798 HP through a Max Machine 1:36 ratio, standard bravo upper and lower cases. Broke the drive twice in 10 years. If I was to build another one, I would go with the SCX upper with either a sport master or sc lower case

The design of the SCX lower housing is the problem area, there's a huge lump in the middle that only got worse when they made the 1400. The only reason to buy an SCX is for durability, running the SCX upper with an SC lower doesn't really make a lot of sense if you're already breaking SC lowers.

[QUOTE=Keith Atlanta;4518778]What about the new SCX blueprinted lower? Looks like its more efficient than an XR by a mile.[/QUOTE

If you're talking about the 1400, look at it up close and then tell us what you think. The bullet is about an inch bigger than the SC so it doesn't match up to a Bravo prop, there's a massive lump in the middle of the housing and on and on.