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Propshaft VS Crank HP ratings..

Old 03-23-2002, 08:28 PM
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I've wondered about these transmission loss stories over the years. According to "BAM" 14 lbs of torque between 4,000 to 6,000 rpms equates to 10.66 hp @ 4,000 rpm, 14.3 hp @ 5300 rpm and 15.99 hp @ 6,000 rpm.

I have a boating buddy wants to do an Arneson application in a small cat. We've heard the transmission eats 50 hp alone and that was too much for him. The drive apparently doesn't eat very much hp at all, so 10 to 16 hp for the transmission, and what, the same amount or so for the drive, makes for a driveline loss of only about 20 to 32 hp. This compared to a Bravo sounds great. Compared to a BMax or other Bravo upgrade sounds even better.

Any thoughts?
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Old 03-23-2002, 09:16 PM
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I agree with Boatless. I think the gears meshing on the right angles are most of the loss. Go out on a limb and say 15 HP for each angle, so a stern drive like a Bravo costs 30 HP, and a TRS with trans cost 45 HP. Bigger gears, more contact area, more loss. I hope Marc will spin a few someday and let us know. Love this board!
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Old 03-23-2002, 09:31 PM
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Seems a little low,a 115hp OMC went to a 88-90 hp when they changed to propshaft rating.A 140 went to a 120.
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Old 03-23-2002, 09:45 PM
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I might be wrong, but I think the corrected HP standard also changed. Anybody know for sure?
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Old 03-23-2002, 10:13 PM
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it sure did-as far as the old mercs--the 140's that were measured at the cranks--are now measured at the prop shaft--115hp--the math is a little fuzzy caus the timing and carbs were tweeked--look at the specs on the sbi PROPSHAFT DYNO--max is somthing around 470 (no torque specs checked)
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Old 03-23-2002, 10:19 PM
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oh yeh--throw the drive oil in there and you loose more hp--the outboard guys need to look for a CLE dry sump system
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Old 03-24-2002, 09:17 AM
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I think that the old way of measuring Hp was done without accessories. That is no alternator, power steering, sea pump, etc. Now they are measured with all accessories attached.
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