Oh cool, only 2 weeks before splashing!

Tom,
Check this out. I was throwing this by JC about the 1:35 ratio XR drive. It has been beefed up at all the critical points. Appears to get around 400 more rpm to the prop.
I wonder if Zup or any of the other guys have tried one.

oops, forgot the link. here it is.


http://www.go-fast.com/sterndrive_gear_ratios.htm

I was running the 1.36 gears on my American Offshore until it blew(250hrs). I swithed to 1.50 and a bigger prop for less gear load like it says in the article. Yes, more speed with the 1.36 but a higher load on the drive gears. Should I go back to 1.36 gears? Let's research it. One good thing is the new XR is alot stronger than the one I had. Thanks FX!

Tom,
From what I read, all those areas were addressed and beefed up to correct any problems. But you did answer my question. I did the calculations on Superbabi, using Kracks figures. Then changing the HP. Says Babi will do 88 with a stock bottom ( his is blueprinted.) But that is in the ballpark of what we were figuring anyway. Then I ran the program with a 1.35 and his speed went to 94. Personally, I think it's worth looking into. Check out the link on the NEW XR drive.

http://www.go-fast.com/mercruiser_bravo_sterndrives.htm


Rick

FX, You are going to gain engine rpm on the other gears but that must be reduced by the different size prop. The only difference in reality is the lesser drag on a smaller pitch prop. The speed difference IMO will be minor. Do I make sense?

Let me add to that. Changing ratio will eather speed up or slow down acceleration. You have a peak rpm limit and that's where you prop it at. If your top speed is 88 with 600hp then you will get there faster or slower depending on gear ratio and prop sellection, but not a big difference in top speed #'s.

most likely loose it out of the hole, but gain on top end. Even changing the prop 2", it still comes out ahead.

One advantage of a custom engine like the 572 or 600ci is it can make peak hp up to 7000rpm if it's not a heavy boat. Equates to faster acceleration and higher top speeds cause you will be able to run a smaller prop and turn it higher rpm.

From what I have read, the best/most efficient Bravo I prop pitch is 28-30".
I have also read that a 1.5 ratio drive is better for the transfer of torque. This makes the most sense as you would have a higher ratio. Remember torque is what really counts...
Last is that most say is that if your boat does not crack 100mph a 1.5 drive is better for over all performance...

The Zuperboat was originally rigged with a 1.36 drive as she ran near 100 with 750HP. Mike also ran with the 1.36 but said that the boat should have a 1.5 for better acceleration.

Gary's boat will likely perform better with a 1.5 ratio drive.
Tom's boat with 800HP will be more on the edge for the 1.36 ratio.

One other thing to consider guys: Professor Jcap and Fastedy are running a 1.5 drives...
They have done more testing than anyone...