That isn't a good comparison. Think about the ten speed bikes but with different size rear tires. The tires represent the prop change in size.

With all things equal with only changing drive ratio, yes, this makes sense. But when changing drive ratio AND prop size both have to be factored in.

So... I still don't get why this would have any affect (other than the prop diameter issue, which is just another factor)

If I understand correctly, using the bicycle as a reference you are using the same power at the pedels but changing the work load with the gear change & trying to compensate for the change with tire diameter. My thought is that the rider would tire faster & more stress would be put on all of the componants. Anywhere close in a nutshell?

you are buying 2 more used bravos. now considering tearing 4 apart and building 2 with used gears to make up for the less than optimal gear ratio. and 1.36's were usually used on high power applications, so the chance of them being in really good shape is less good. you are gonna tear 4 drives apart and then have 2 rebuilt correctly and have a big pile of parts that are worth very little disassembled and not good enough to justify reassembling. get your existing drives fixed, or buy 1 used one of the correct ratio.

both bikes will probably sink anyway.

1.36:1 gears transmit less torque to the prop than 1.5:1 gears.
Counter to what has been said already, this allows the drive to handle a bit more power by trading torque for rpm. Rpm is not what hurts drives - excess torque is (at least when we are talking about less than 6000 rpm).

What you need to know is that the B1 lowers all use the same gears. The different ratio is in the upper gears. A 500 ft lb 502 Magnum with a 1.5:1 Bravo will send 592 ft-lb of torque down the vertical shaft into the lower gears. Then you end up with 750 ft-lbs at the prop.

The 1.36:1 Bravo with the same 500 ft-lbs of motor, will send only 537 ft-lbs down the vertical shaft, and only 680 ft-lbs at the prop. When you are pushing more than 470 ft-lbs into a (non X or XR) Bravo, you're going to end up being towed in at some point. In heavy boats running more than a 454 Mag, the 1.36:1 gears are one excellent way to preserve the life of the drive.

Less torque at the prop DOESN"T MEAN that you can't go fast, because you have additional prop speed. And prop speed x pitch is what does the work.

Propped for the SAME wide open throttle RPM, you will likely be within 1 mph of the same ultimate speed. It boils down MORE to which prop blade is matched better to your boat's weight at its propshaft rpm.

You will find people swear that 1.5:1 gears worked better on their boat, and you will find people who swear that 1.36:1 gears worked better on their boat.

A buddy and I had identical 502 Mag powered Formula 311's. The boats were almost identically equipped. The boats ran within 1 mph of each other. He blew up his original 1.36:1 drives and replaced with 1.5:1's. After messing with props, he lost a definite 1 mph. One prop size up, and he lost mph, and one prop size down, and he lost mph. His boat never matched mine for speed again. I blew my drives up, and went back with 1.36:1's and remained a little faster than him. That's about as "apples to apples" as I can give you.

Every now and then, a prop manufacturer has a particular blade that just turns out "better". In other words, let's say the 24 pitch XYZ prop just seems to be magic in a certain application. You can put steeper gears in, and spin a 22 XYZ and not get as good of performance, and you can put more gear in and spin a 26 XYZ and not get as good of performance. In cases like that, it's the "magic" blade that is the reason for better performance.

The same thing goes for some of the popular props. In those cases, the gear ratio that will allow you to run "that prop" may be desirable.

If you blew up your 1.5:1 drives, and you have access to some good 1.36:1 drives cheap, then get them. Play with props. The end result will be fine.

If money is no object, or you can get 1.5 drives for the same money, then stick with what you've got.

MC

I'm just impressed w/ his 74mph in that hull w/ those motors & that he's turning 28's?

GPS #'s?

Yes I was buying them (actually did), they came stock on the identical boat 91 instead of 94 with slightly less hp 385 vs 415. Have all new bearings, seals, etc. They are mint, thanks (Nordic95).

Yes, 100% gps, it's usually in the 73 range but the props are kinda sh1tty.

Pics are 1.36 drive(s), gps and damaged 28's

You and I are on the same page... you are splitting hairs more though. Bottom line is prop + gearing makes the end result.

A huge reason for gearing is props and prop speed. Props are only effective within a finite range of pitch. The kicker in changing gear and props (which can lead to your what you are saying about +- 1 mph) is the diameter of the props are generally different as pitch changes.

???

Mercs complete line of Bravo 4 blades are the same diameter from 22 to 34 pitch

This comes from my particular case, sorry about the confusion. Donzi set up the 28 ZX to run with the Mirage plus. The Mirage plus does change size...

From the factory they were setting boats up with 350 Mags / 1.5 drives / 23p M+ props.

I got my boat... 6.2 (377Mag) / 1.65 drives / 23p M+

Hit the limiters (obviously). They had me try 25p M+ but I still get planing issues that guys with the 350's/1.5/23p props don't have. I am thinking this is a diameter issue. From one of the factory workers: Donzi went as aggressive as they could on the X dimension on this boat. So I'm thinking that I'm just a shade too high with the bigger pitch, smaller diameter props.

With the Bravo 1's I'm fine.