chris82007

Hi Everyone.

I need a new B1 outdrive.
Current B1 is a 1.5 ratio and I run a Mirage Plus 21 to 5000 rpm @55mph

I sometimes like to run my Mirage Plus 23 but my hole shot sucks and upper rpm is down a little, I forget but I think around 45-4600 rpms.

Would going to a 1.65 B1 help the hole shot running the 23p?

Thank you!

302Sport

According to prop slip app the 1.65 will put you at 5020RPM with a 23P at 55mph, and yes, a 1.65 will give you more torque.

Griff

Going to a 1.65 will give you an increase of 500-600rpm using the same prop

Tartilla

​What is the benefit? Seems like the change cancels itself out.

Am I missing something?

SB

iTrader: (1)

Some formulas and fountains used 1.65 gear bravo drives. Also, Years back a few prop shops around then would say the 28” bravo prop was one of the best. Interestingly, the boats i mentioned usually had 28” bravos. Sometimes 26” ‘s.

302Sport

Theoretically spinning a higher pitch prop slower is putting more torque to the water.

Tartilla

Is this a phenomenon of the hydro dynamics of less frictional loss of the faster spinning lower pitch prop?

Must be a chart of efficiency much like a turbo efficiency chart.

Is it more tq to water, or less loss so more net tq?
​​
I've always preferred to get more rpm (within reason) and a lower pitch. Easier on gearing & trans, and doesn't lug the engine.

302Sport

It’s just always the preferred setup. If he could find a set of 1.85:1 drives and spin a 26P the boat would probably run even better.

302Sport

You’re talking about just slapping a higher pitch prop on and lowering your RPM’s. I’m talking about changing gear ratios and pitch for the same net rpm.

Brad Christy

Tartilla,

I'm with you. A prop is nothing more than another gear in the drive train. If you gear up at one end, then gear down at the other, resulting in the same final gearing, I'd think you've wasted your time/money/effort. There are obviously other factors at play, parasitic loss due to drag in the drive line and at the prop, differences in hydrodynamics from one prop or prop style to the next, etc, and I suppose one could potentially find some magic sweet spot between prop pitches that didn't exist with the original outdrive gearing. But to change the gearing in the outdrive, only to gear it back to starting final gearing with the prop seems pointless unless you're chasing some other factor.

Thanks. Brad.