Propshaft VS Crank HP ratings..
#3
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A better rule of thumb is to figure about 6% loss between crank and prop with non-transmission drives like the Bravo. (The higher the load, the more friction you have to deal with.) Losses through transmissions will be higher.
Example: Hp500 x .94 = 470 propshaft hp (as rated by Mercury)
Example: Hp500 x .94 = 470 propshaft hp (as rated by Mercury)
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#4
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The higher the load...
C_Spray - Does that mean that if I put 600 HP through a bravo the loss will be more than 6%? Is it also true that losses through gears are related to RPM as well, maybe RPM squared or cubed?
Where's Rambunctious....what do you say?
Where's Rambunctious....what do you say?
#5
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tomcat, I would say that the 6% covers the additional loss.
6% of 500= 30
6% of 600= 36
I've heard that the transmission drives, absorb more hp the heavier they are built. I think I read where the Merc drive absorbs 20hp and the Borgwarner absorbs 30hp. Some of the guys that work on these Trans may know a little more exact.
6% of 500= 30
6% of 600= 36
I've heard that the transmission drives, absorb more hp the heavier they are built. I think I read where the Merc drive absorbs 20hp and the Borgwarner absorbs 30hp. Some of the guys that work on these Trans may know a little more exact.
#6
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We have a dyno that actually measures the power required to turn a transmission (or crash box for that matter). See Trans Tester for details. On the average, the torque required to turn a stock Velvet drive (current model, the early ones are worse) is about 18 ft lbs any place between 4000 and 6000 rpm, it does go up a bit after that. One of our modified units takes about 14 ft lbs and our dry sump is about 10, and goes up to 12 or so at 7000 RPM. A regular crash box is about 5 ft lbs. When in forward there are no gears involved, so as far as the engine is concerned the transmission is just a straight connection to the drive (with the above drag). The loss as a result of the transmission is fixed and not related to load or any kind of percentage, but of course HP = RPM x TORQUE/5252 so the loss does go up with RPM.
One of these days I will make the adapter to hang a drive on it and at least get an idea of the no-load power required just to turn it.
One of these days I will make the adapter to hang a drive on it and at least get an idea of the no-load power required just to turn it.
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Marc
www.mercruiserparts.com
www.go-fast.com
www.bammarine.com
www.cyborgtransmissions.com
It's not alive -www.BoatStuffExpress.com - temporarily retired
#7
Marc, That's exactly what we need!! Make the adapter and then test the TQ required to turn the drives.
XZ, XR, IMCO Extreme, IMCO SC Extreme, B-Max.
1.5 and 1.36 ratios.
3000-6000rpm.
Mercury lube and then amsoil synthetic lube.
OK, are you done yet. We need this data. Hey Tomcat, are you interested?
XZ, XR, IMCO Extreme, IMCO SC Extreme, B-Max.
1.5 and 1.36 ratios.
3000-6000rpm.
Mercury lube and then amsoil synthetic lube.
OK, are you done yet. We need this data. Hey Tomcat, are you interested?
#9
This info could help explain the speed loss some are experiencing with the XR and B-MAX drives. The effect of ratios, rpm's, and synthetic lube would be very enlightning.
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the math is pretty clear--every right angle eats up a curtain percentage--thats why the motorcycles (that race/go fast) use chains--less right angles--the V-MAX kit from driveshaft to chain makes a big difference as far as rear wheel hp.