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Titan
09-16-2010, 12:25 PM
I am upgrading my upper to an XR with my Imco shorty and wondered if I should make a gear change? I am running a 29 pitch Mirage prop and wondered if there was any advantage to changing from 1:50 to 1:36 gears and spinning a smaller prop faster? I've been told that it makes some boats handle better and there is definately more props around to try in the smaller sizes. I was looking for a 29 hydromotive Q4 as the 27 I tried worked really well with less porpoise than the bravo 1 that i was running. Unfortunately I goes to the rev limiter with the 27.

Any thoughts would be appreciated!! Thanks in advance for your advice.

mrfixxall
09-16-2010, 12:43 PM
I am upgrading my upper to an XR with my Imco shorty and wondered if I should make a gear change? I am running a 29 pitch Mirage prop and wondered if there was any advantage to changing from 1:50 to 1:36 gears and spinning a smaller prop faster? I've been told that it makes some boats handle better and there is definately more props around to try in the smaller sizes. I was looking for a 29 hydromotive Q4 as the 27 I tried worked really well with less porpoise than the bravo 1 that i was running. Unfortunately I goes to the rev limiter with the 27.

Any thoughts would be appreciated!! Thanks in advance for your advice.


you will lose the acceleration and the boat wont be as snappy!

RickSE
09-16-2010, 03:14 PM
I've always heard that you want to go the other way on gears and that higher pitch props are more efficient and have less slip, but selection does get harder. Less gear and smaller pitch will put less thrust into the drive though.

yeller
09-17-2010, 01:41 PM
Why upgrade? Why not run the Bravo until it breaks......and that may never happen. Example: My cousin has 1900hrs on his and it's never been apart. At least 1500 of that is with the same or more power than you're running.

Dr. David Fleming
09-17-2010, 01:59 PM
Race engine builder Tyler Crockett just covered this subject in the current issue of Performance Boats - Sept 2010 - his advice is if you are using over a 32P pitch prop the efficiency of the prop is reduced and a gear change to a lower numerical ratio is desired. 1.50 to 1.36 for example. Tyler's reasoning is "...the lower you get your prop slippage down, the more load your are putting on your drive. I have run 32" - pitch props, but any pitch over that, and the bigger props don't seem as efficient. I would use the 1.36 and use the 30" or 32" prop..."

On my Donzi 22ZX - Tyler bitches about me using the 30P prop on my Bravo I Performance drive because "I am loading it" but when I ask him about changing to the Bravo XR he says "no because the XR is a stronger drive but its a slower drive through the water than the the Bravo I" - go figure - do you really need the XR or not?

Planetwarmer
09-18-2010, 02:59 AM
Race engine builder Tyler Crockett just covered this subject in the current issue of Performance Boats - Sept 2010 - his advice is if you are using over a 32P pitch prop the efficiency of the prop is reduced and a gear change to a lower numerical ratio is desired. 1.50 to 1.36 for example. Tyler's reasoning is "...the lower you get your prop slippage down, the more load your are putting on your drive. I have run 32" - pitch props, but any pitch over that, and the bigger props don't seem as efficient. I would use the 1.36 and use the 30" or 32" prop..."

On my Donzi 22ZX - Tyler bitches about me using the 30P prop on my Bravo I Performance drive because "I am loading it" but when I ask him about changing to the Bravo XR he says "no because the XR is a stronger drive but its a slower drive through the water than the the Bravo I" - go figure - do you really need the XR or not?

It takes more HP to turn a heavier drive. The XR will most likely rob more power than the Bravo 1.