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Blown Scarab
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i have a 31 ft scarab 10,000 lbs, with 2 blown 500 inch chevy big blocks with BDS 8-71 blowers with super chillers,, they are hydralic roller motors and turn about 5100 rpms, and run 94-98 mph, gps depends on how much fuel and how many people in the boat, 26 pitch 3 blades are on it, not cleavers. thanks in advance.Pushing 5 1/2 pounds of boost.
 

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Souns like you must have a 1.34 gear ratio in your outdrives. 26 inch props at 5100 rpm dont go 90+ in a 31 scarab. What do you really want to know? Do you want more RPM?. Better handling, better cruise?
 

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Is 5100 RPM the max the motors will pull at WOT? If so, I wouldn't go to a larger diameter prop. It will only reduce the rpm's and lug the motors. It sounds like the RPM's are pretty good right now. You could possibly try a 4 blade Bravo style prop, tey tend to get on plane a bit better than a 3 blade, and have a bit better cruise speed....but... if your boat planes easily, it may not be worth it. Props will run ya 400 bucks each, so it's a lot of money for a small possible increase of performance.



Darrell.
 

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5100rpm, 26 inch pitch, 1.5 drive ratio, 10% slip is 75mph

5100rpm, 26 inch pitch, 1.34 drive ratio, 10% slip is 84mph

5100rpm, 26 inch pitch, 1.34 drive ratio, 0% slip is 94mph

What outdrive do you have? What ratio is it?
 

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I agree. 26" pitch at 5100rpm and 94-98mph don't add up.

As asked before, we need more info on everything to even try to help. Engine parts/specs used, outdrive gearing, etc,etc.

No valuable info = no valuable answer
 

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Get a GPS or Iphone app. Get dyno sheet or find out what peak [email protected] RPM. Park your props right on top of HP peak and let the cruise fall where it falls. Another concern is the Bravo IIs. What is your prop centerline to the bottom of the boat?
 

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I would give Hydromotive props a call

They have the experience and prop styles

However, you need to supply your info in a orderly manner

i,e boat hull, true weight, dyno sheet, drive make, height, gear ratio and use

I bet a 5 blade would give you best overall and fuel mileage
 

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agree

I agree that they have experience and prop styles. I usually go out and get all the information, writing it down on a legal pad before I call. They may ask questions that you don't anticipate. Go ahead and jot down everything you can and go from there. I would also find out of they work on delay timer or not.
 
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