More prop or lower gear ratio?
10-21-2014, 12:15 PM
#21
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I had this very issue in my 28 Nordic. I was trouble finding correct prop and the bigger I went (above 30P) the worse it handled, and I was limited by the RPM that I turned or could turn. I went with 1.36 and 28P. Boat goes faster, handles way better and I have room to grow. (although I've tried bigger props with the 1.36 and they don't work as well as the 28P.
Boat accelerates as fast as it ever did.
Good luck-
Boat accelerates as fast as it ever did.
Good luck-
10-21-2014, 12:41 PM
#22
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basically in a nut shell and not to go into huge depths here - as we all know gear ratios move your rpms up or down - your engine makes its peak torque levels down lower than your peak HP up higher (rpms) Torque is what gets these boats up and running. Moving rpm levels up or down moves your peak torque levels - you do not want your peak torque levels down too low or way up high on your rpm range. making peak torque high on the rpm range will make a pig of a boat for cruising - getting on plane, getting out of its own way and so forth.
To further look at it - for longevity of any marine engine, they will last longer running at 75% duty cycle for load periods of running. That duty cycle of 75% is within the range of your peak torque #s. I am basically talking about stock to medium performance set up marine engines built with production parts to above duty performance parts here.
To further look at it - for longevity of any marine engine, they will last longer running at 75% duty cycle for load periods of running. That duty cycle of 75% is within the range of your peak torque #s. I am basically talking about stock to medium performance set up marine engines built with production parts to above duty performance parts here.
10-22-2014, 03:55 AM
#23
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I had the same hull as you and I ran a 1.36 ratio with a stock 30 pitch bravo 1 4 blade prop. The boat would run 92-94 mph @ 5200-5300 rpm all the time. If your looking for 6000 rpm with a 1.36 ratio you may have to go to a 26 pitch or lab your 28, depending on how much torque your making. The boat would get on plane and accelerate very good but it had a little help with a vortech supercharger making over 800 ft # of torque.
10-22-2014, 10:01 PM
#24
Charter Member # 55
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Are you under propped ?....if the 28 pitch prop is letting the engine run in the proper rpm range with a 1.5 ratio drive, and you change the drive ratio to 1.36 ( less gear reduction, faster prop shaft speed than the 1.5), you'll need to drop DOWN at least 1 size in pitch to maintain the same engine rpm.
If you are under propped and have about 1000 rpm left over, you could probably go to the 1.36 and use the 28 pitch prop.
Bravo's start to lose their efficiency above 32" pitch
If you are under propped and have about 1000 rpm left over, you could probably go to the 1.36 and use the 28 pitch prop.
Bravo's start to lose their efficiency above 32" pitch
Going to a 1.36 from a 1.5 is around a 600rpm/3" of pitch difference.
10-23-2014, 08:20 AM
#25
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I'm under propped now and hit the rev limiter with the 28p and testing with a 30p indicated that might not be enough either. If I get better acceleration with a 1.5 and a 32p then a 1.36 and a 18p then that makes the most sense for me.
