Bravo drives gear ratio change
 

I have 38' T/S Cig Top Gun with Bravo I drives. They currently are 1:36 ratio with 26 pitch Bravo props pushing just under 600hp. Top speed is 87mph but 84mph all day. They have given me no problems whatsoever but I know it's a matter of time so I'm gentle with them. I am giving serious consideration on the XR upgrade this winter (which is all the budget will allow). All of the local guys tell me to switch to 1:50 gear ratio for better performance. Will this give me any difference in top speed of the boat or is it just mid-range? I feel the current set up has plenty of punch in the middle. Am I correct in that the 1:36 ratio is a little easier on the drives? Just looking for some feedback..... Thanks

I switched from 1.36 to 1.5 on my 38 Powerplay. Picked up 4 mph and there is probably more to be had. It did cause a number of other issues when I made the change. I don't have Bravo's though, I have B-max's. I did run in to some issues.

The gear change drastically increased leverage and I had to add spacers to drop the drives down another 1" to get the boat on plane. I tried the drives 1 1/2" deeper, but raised them back up 1/2". Sure I could have purchased some 5 blade props, but I was worried about breaking gears due to the extra bite. I wanted to stay with 4 blades.

I went from 26 Bravo 1's and am currently turning 32's but also have a set of 34's. I rarely run my boat WOT, so top speed is not an ultimate concern. I made the switch when I was freshening the drive since it needed new gears anyway.

I guess what I'm saying is be prepared to do some tweaking if your prop shaft depth is fairly high and have a good assortment of props to test.

I was told just the opposite as far as the 1.5 gear ratio being easier on the drives.

XR's arent bullet proof.

A friend of mine has a 02' 38 TS TG w/500EFI's and XR's

In 09' we put a upper gear set in one side because
the teeth were falling apart, last year the opposite side
broke a tooth off and junked a whole upper out.

And then there's my experiences with them on my own boat, but it's depressing, so I'll spare you.;)

Also XR's consume a little bit more power than the standard helical gears do, so be prepared for a slight speed loss.

If you're really looking for a better mousetrap look at a IMCO
SCX, or the BMAX ( they're under new ownership)

What he said!

John, how did changing the gear ratio increase leverage? I'm lost on that one buddy.

Probably a bad choice of words. Torque at the prop would change. ie: an engine producing 1000 ftlbs of torque would have 1360 ftlbs at the prop with 1.36 gears and 1500 ftlbs with 1.5 gears. Maybe my logic is off or I'm missing something. I know you spent a lot of time on the setup on your 29 Outlaw. See this thread about my gear change experience. http://www.offshoreonly.com/forums/d...ng-advise.html

It's all smoke & mirrors & magic buttons to me, but I see what you're theorizing.:drink:

I would think that keeping the gears closer to 1:1 would be easier on the gears and turning more rpm at the prop would also be easier on the drive (less torque per revolution on the propshaft and lower part of the drive). I suspect the speed difference could be due to less slip with the larger pitch prop at hight speeds. These are just my basic engineering thoughts. There are always trade offs.

Excellent feed back. You have me a bit concerned because my drive height is a bit on the high side. I have had others recommend the 5 blade props but I would tend to agree that the four blades would be easier on the drives.

I know XR's are not bullet proof but consider I was told the Bravo I's wouldn't last a season, so I still consider it an upgrade over my current set up.

I would hate to lose any top end with the ratio change...which is my basic question

As far as prop shaft depth. Mine with NO spacers is 2" below the transom. I am currently at 3 1/2", but have also tried 2 1/2" and 4". It is amazing the difference that 1/2" makes.

How you treat the sticks is going to have a BIG effect on the life of the gears and drives.

I've heard the Bravos have less drag and will be the fastest. You will most likely lose MPH with the XR's, IMCO's and B-Max's, but you will gain strength and reliability.