Gear Ratio / Prop Pitch Question
04-16-2003, 01:09 PM
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Gear Ratio / Prop Pitch Question
Question...
How do you determine best gear ratio prop pitch for your setup. I currently have a Donzi 22 Classic with a 454MAG (385hp) and a 1.5R Blackhawk drive. I am currently spinning a set of 29P props at 4400 RPM max. I am seeing 71.5 or so GPS, so that gives me about an 10% - 11% slip factor...
My question is this, should I just put on a pair of 27P props to get my RPM to where it should be, around 4800 - 4900 RPM or so, or would you regear the drive to a 1.65R, and use a set of 31P props? Would changing the gear ratio help me to get my engine up into the powerband? How much does a kit cost to upgrade the gears to the new Bravo X style?
Thanks!!
Woodsy
How do you determine best gear ratio prop pitch for your setup. I currently have a Donzi 22 Classic with a 454MAG (385hp) and a 1.5R Blackhawk drive. I am currently spinning a set of 29P props at 4400 RPM max. I am seeing 71.5 or so GPS, so that gives me about an 10% - 11% slip factor...
My question is this, should I just put on a pair of 27P props to get my RPM to where it should be, around 4800 - 4900 RPM or so, or would you regear the drive to a 1.65R, and use a set of 31P props? Would changing the gear ratio help me to get my engine up into the powerband? How much does a kit cost to upgrade the gears to the new Bravo X style?
Thanks!!
Woodsy
04-16-2003, 01:22 PM
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For best performance, spin your engine up to 5000-5100rpms. I would just change rpops to the 27's, then see where you're at. Still might need some more rpm. Then you can get them labbed.
04-16-2003, 05:55 PM
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Woodsy,
am I correct in assuming that you added a Blackhawk to a standard 22 Classic? If yes, you will not have the rocker which most factory Blackhawk hulls have.
What is the distance of the centerline of the prop shaft to trailing edgge of the hull?
With the power you have, the boat should be faster. I assume it is one of the above issues that is off.
My personal preference would be the taller gear ratio, but I will admit that the 1.65 ratio is more fragile, which especially with a Blackhawk may become a problem. Blackhawk props are becoming difficult to find. Let me know if you wantt to test 27s and can't find any.
am I correct in assuming that you added a Blackhawk to a standard 22 Classic? If yes, you will not have the rocker which most factory Blackhawk hulls have.
What is the distance of the centerline of the prop shaft to trailing edgge of the hull?
With the power you have, the boat should be faster. I assume it is one of the above issues that is off.
My personal preference would be the taller gear ratio, but I will admit that the 1.65 ratio is more fragile, which especially with a Blackhawk may become a problem. Blackhawk props are becoming difficult to find. Let me know if you wantt to test 27s and can't find any.
