HP losses from Bravo 1X drive
Gold Member
12-19-2006, 08:36 AM
#4
Registered
Re: HP losses from Bravo 1X drive
Rage,
25/30 horspower with a XR. Not much if any difference with the X. Mercury rates their black motors at the propshaft, which became industry standard years ago. They rate their HP/racing/blue motors bobtail, and propshaft.
examples are:
496MagHO crankshaft ?/425 propshaft "black"
HP500EFI-500 crankshaft/470 propshaft "blue"
HP525EFI-525 crankshaft/500 propshaft "
HP575SCi-575 crankshaft/550 propshaft "
Regards,
Steve
25/30 horspower with a XR. Not much if any difference with the X. Mercury rates their black motors at the propshaft, which became industry standard years ago. They rate their HP/racing/blue motors bobtail, and propshaft.
examples are:
496MagHO crankshaft ?/425 propshaft "black"
HP500EFI-500 crankshaft/470 propshaft "blue"
HP525EFI-525 crankshaft/500 propshaft "
HP575SCi-575 crankshaft/550 propshaft "
Regards,
Steve
12-19-2006, 10:47 AM
#7
Re: HP losses from Bravo 1X drive
So are you saying that the HP loss from a Bravo One, a Bravo One X and a Bravo One XR drive is pretty much the same ?
Around 25-30 HP ?
I am no expert in transmission loss in a sterndrive, but find it interesting, and I would guess it is dependent on the RPM's ?
So probably the 25/30 HP loss is valid around 5000 RPM's seen from the crankshaft end ?
And at lower RPM's the HP loss is not so much ?
or how does this work ?
Around 25-30 HP ?
I am no expert in transmission loss in a sterndrive, but find it interesting, and I would guess it is dependent on the RPM's ?
So probably the 25/30 HP loss is valid around 5000 RPM's seen from the crankshaft end ?
And at lower RPM's the HP loss is not so much ?
or how does this work ?
12-19-2006, 01:09 PM
#8
Registered
Re: HP losses from Bravo 1X drive
Phazar,
That's what Mercury says, and they have excellent test instrumentation (dynos), so I think 25/30 HP is close.
As far as the differences in the drives, and there are some, such as straight cut gears vs helical cut gears, and heavier bearings and carriers, it isn't going to make that much difference. The frictional losses come (primarily) from 2 sets of 90o gears, 1 universal joint, and a wet sump in all of them.
I have no idea what the HP loss is at partial throttle settings, and I doubt if anyone really cares. 99% of the people on this website are setting up fror maximum top end #s, and your midrange #s are what they are.
I think Rage, like most people, is trying figure out what the WOT HP loss is.
In a wet sump drive, the best gains to be made in heat reduction and frictional losses come from synthetic oils, like
Amsoil, Redline, Royal Purple, etc. Even though they are lower in vicosity, their shear strength is higher. I think we are getting into "Hydrocruiser territory" here. Check out his threads for more information on engine and drive lubricants.
Regards,
Steve
That's what Mercury says, and they have excellent test instrumentation (dynos), so I think 25/30 HP is close.
As far as the differences in the drives, and there are some, such as straight cut gears vs helical cut gears, and heavier bearings and carriers, it isn't going to make that much difference. The frictional losses come (primarily) from 2 sets of 90o gears, 1 universal joint, and a wet sump in all of them.
I have no idea what the HP loss is at partial throttle settings, and I doubt if anyone really cares. 99% of the people on this website are setting up fror maximum top end #s, and your midrange #s are what they are.
I think Rage, like most people, is trying figure out what the WOT HP loss is.
In a wet sump drive, the best gains to be made in heat reduction and frictional losses come from synthetic oils, like
Amsoil, Redline, Royal Purple, etc. Even though they are lower in vicosity, their shear strength is higher. I think we are getting into "Hydrocruiser territory" here. Check out his threads for more information on engine and drive lubricants.
Regards,
Steve
Last edited by Steve Zuckerman; 12-19-2006 at 01:45 PM.
12-19-2006, 01:50 PM
#9
Re: HP losses from Bravo 1X drive
I know a pretty good answer has been provided to the question.
I am just wondering what the real answer is.
The reason I asked is that I don't think it can be a "permanent" loss of 25/30 HP across the RPM range, otherwise you would not be able to turn the shaft in gear using your hand. At least that is what I think using my own logic.
Actually I was thinking whether the drive HP loss, is a percentage of the engine HP power output ?
I know this is theoretical, but if it is e.g. a percentage of the engine HP power output, then the answer to the question is it depends on the power output of the engine.
Really I ask because I like to understand how technical things on my boat work, and there are so many knowledgeable people on this board so may be somebody knows ?
I am just wondering what the real answer is.
The reason I asked is that I don't think it can be a "permanent" loss of 25/30 HP across the RPM range, otherwise you would not be able to turn the shaft in gear using your hand. At least that is what I think using my own logic.
Actually I was thinking whether the drive HP loss, is a percentage of the engine HP power output ?
I know this is theoretical, but if it is e.g. a percentage of the engine HP power output, then the answer to the question is it depends on the power output of the engine.
Really I ask because I like to understand how technical things on my boat work, and there are so many knowledgeable people on this board so may be somebody knows ?
12-20-2006, 08:37 AM
#10
Re: HP losses from Bravo 1X drive
I think that the real truth is that the drive requires TORQUE to turn and at WOT around 5252rpm (where TQ=HP) it requires 30 lb-ft of TQ which is equal to 30 HP. Now at a lower rpm say 2626rpm it will still take the same TQ 30 lb-ft to turn but at this rpm it is only 15 HP. Torque is what we measure!
