Bravo basics in gearing
 

I apologize if this has been beaten to death already but I did a search with no solid answers.

My Bravo 1 originally had the 1:5 ratio but the previous owner changed it to 1.65:1. Is the gearing change in the upper, lower, or both? Can I just buy one half with the 1.5 ratio?

Also, does a billet top cap help reliability?

My Baja 272 is currently propped with the 1.65 setup but I just upped the power and figured reverting back to the original ratio would be easier than buying new props as I have a variety for different conditions.

The upper gears change the ratio for a regular Bravo

Buying a prop will be much cheaper.

I'll probably just grab another whole drive and keep this one as a spare. Anyone try the billet caps on the B1 with any improvement? I heard that it helps keep the cases from flexing but haven't heard any first hand experience.

How much Power did you add??

Unsure yet, but it should be right about 600-650 total. I know a B1 is inadequate but have read everything from people running their 800hp with no problems to blowing them up with the stock 454 mag. I'm just hoping to get through the summer and sort that out next winter.

gear ratios go hand and hand for where the highest torque output lands in what rpm range. That range is important for marine apps

If you added more than about 100-120hp, then the gear change from 1.65 to 1.50 will probably not be enough to reuse the props you have anyway.

How do you determine what ratio you are running? I have #6's and would like to learn.

If the drive is off, you can count revolutions of the drive input shaft, compared to the prop. If it is a 1.5 drive, the propshaft will make 1 turn, and the input shaft will make 1.5 turns, or to make it easier to see,, for every 3 turns of the input shaft, the propshaft will turn 2 times.

Appreciate the explanation 33. I couldn't find that anywhere.
Matt

It was slightly over-propped to begin with and the gear change calculated out to be a 2pitch difference. I've seen some B1 top halves go for pretty cheap and was entertaining the idea of grabbing one to see how things worked out before going big on a whole new drive. I think that I may end up jusr upgrading the drive and start swapping props to get the right fit.

Roughly and generally speaking, is a B1X drive good for about 650hp on a 27' 5Klb open bow boat, or should I just head straight to the classifieds for an XR drive? From what I've read a billit top cap and plenty of cooling goes a long ways for longevity.

Are there ggod and bad years for bravos? My current unit is a 1996 OL unit.

We do it a different way. Turn the prop shaft 10 turns, count the input. Divide input count by propshaft turns (10) , so 15/10 = 1.5, 13.5/10 = 1.35, etc.

Makes it a little easier when the ratios are close.

good idea, thanks

Also the weak link in a bravo is the upper. So a second upper is what is most needed for a spare to get thru the weekend anyway...