HP losses from Bravo 1X drive
 

What is the HP loss through the Bravo 1X drive (1.5 gear ratio)?

Re: HP losses from Bravo 1X drive
 

30 Hp But Don't Take My Word For It

Re: HP losses from Bravo 1X drive
 

Why not? What do you suggest?

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

Re: HP losses from Bravo 1X drive
 

I WAS NOT SURE 100% SURE.

Re: HP losses from Bravo 1X drive
 

Thanks gentlemen.

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 ?

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

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 ?

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!

Re: HP losses from Bravo 1X drive
 

So has anyone ever tested different drive oils and compared hp loss??? or compared synthetic to conventional?

Re: HP losses from Bravo 1X drive
 

Actually HP is the rate of doing work. The HP losses in the drive is purely do to friction which is converted directly to heat. That heat is why for higher HP engines the drives require drive showers to help remove that heat so as to survive. Lower HP engines do not require drive showers though it sure does not hurt. The HP losses in a drive at any point in time is a function of how much HP is being transferred through that drive or a percent of that HP being transfered. It is generrally assumed that this percentage of frictional loss is basically fixed thought that does not have to be the case. Different drive designs can have different drive HP loss characteristics.

In general as Steve mentioned the main interest about drive HP losses in this site is in regard its effect on the remaining HP available at the prop shaft at WOT for top boat speed. Also of related interest is to be able to accurately compare / corrolate an engine's bench dyno test data/ratings with that from a prop shaft dyno test as obtained through the drive.

I take the 25-30HP Bravo1 drive loss to be associated with motors in the 500HP - 525HP range. I would not expect a 1500HP Stirling to only experience 25-30HP loss through a Bravo 1 if that drive could in fact survive the torque of that motor.....not.

If I am in error on the 25-30hp Bravo 1 drive loss being associated with the 500HP - 525HP range motors please advise.

Re: HP losses from Bravo 1X drive
 

Rule of thumb: one set of gears is 98% efficient (2% loss due to friction). For ease of calculation I assume this loss is constant, it does not increase with RPM or load. But pumping losses, as in wet sump gears flinging oil around, are not constant, they increase faster than RPM (the percentage loss increases with RPM). And if the load on the gears exceeds a certain contact stress, or proper lubrication conditions go away, then friction at the gear teeth may increase and the percentage loss increases to more than 2%.

So a Bravo drive handling 500 HP and delivering 470 HP to the prop is 94% efficient, but push it beyond that 500 HP @ 5200 RPM and it might be only 90% efficient. Convert to dry sump, change oil viscosity and treat the gears to reduce surface roughness and you get some of this back.

To answer the original question, you are close enough if you just assume a 6% loss at all RPM up to 5200. So if you are cruising at a speed that requires 300 HP at the prop, the engine must deliver 318 HP at the crank. The loss is 18 HP. At 200 prop HP the loss is 12 HP etc.etc.

P.S. The HP loss through a Bravo drive at 1500 HP is 1500 HP. :D

Re: HP losses from Bravo 1X drive
 

What about losses at 5,500rpm? 6,000rpm?

Re: HP losses from Bravo 1X drive
 

Ron,
When I was drag racing, the gearcase guru David Steckbauer (formerly of Mercury Racing) and I had several lengthy conversations on this matter.
David's trickest piece is a small 4 1/4" V6 (for the MercXR150) gearcase machined down internally to accept the larger billet bearing carrier and gears for the racing 2.5s, normally in a 4 3/4 housing like the Sportmaster. This may seem trivial, but in spec class racing where every little detail could not be overlooked, this is a really trick item.
It had been rumored that removing the seldom used reverse gear could free up as much as 10/15 horsepower, in these cases. I asked David if this was an urban/racer myth or true.
I could give up reverse easily on a race boat for 15 "free" HP.
He said maybe 1-2 horsepower on a 300 horsepower motor, but I doubt if you will ever feel it or measure it (ET/MPH), because there are so many other variables that have a greater effect on HP, like weather and tuning.
This research was going on at Mercury during the heyday of factory racing (F-1, Mod-VP).
We went on to lubricants. He said this where Mercury was able to pick up discernable HP increases. He said using lightweight synthetics, with high shear strength, netted as much as 10 HP at high RPM (in this case 9000+) and reduced operaing temps considerably, which helped the small volume speedmaster live through a 50 lap circle race on an F-1.
Since drag racing is high horsepower (I was making 600+), but short duration, most of serious hitters adopted this theory.
Some guys were actually running transmission fluid. I used a thin weight Alisyn synthetic in mine.
David says people often confuse (high) viscosity with protection. With petroleum based lubes that is mostly true. He says with synthetics it isn't. They did Timken bearing test on all kinds of oils, petro and synthetic, and the the synthetics, were much better overall, had higher shear strengths, and allowed a decrease in viscosity, which freed up horsepower.
Obviously, Mercury carried this even a step further in their racing inboard drives, by dry sumping the #6 drive, and using synthetic oils.
Regards,
Steve

Re: HP losses from Bravo 1X drive
 

Thanks.

Yes, at 1500HP the drive losses are no longer converted to heat but instead converted to the acceleration of the molten metal that was the drive into space.

Re: HP losses from Bravo 1X drive
 

I was told by an engine builder that the difference between my engine's horsepower on the dyno and what I'll actually see at the propshaft is a fixed number of about 25-30 HP at WOT, regardless of the horsepower of the engine. You simply subtract that amount of horsepower.

The reason that makes sense to me is that you can think of the drive as a "black box" with a set of gears, bearings, universal joints and a particular lubricant. At every RPM you turn the input shaft, there will be a corresponding amount of resistance that will have to be overcome by the driving force of the motor. The drive doesn't care if it's got a 50 HP electric motor or a 1000 HP blower motor turning the input shaft - the internal resistance of the drive is going to be the same at any given RPM.

Tomcat's example of using a percentage reduction for a single engine situation works. However, using a percentage reduction in horsepower from one engine to the next could be misleading. Calculating the percentage reduction in horsepower in those two examples, subtracting 30 HP from 50 HP leaves 20 HP at the propshaft for a 60% loss, and in the second example, you'd only see a 3% loss. That's why I don't think it's helpful to try to use percentages to predict the difference between crankshaft horsepower and propshaft horsepower. It's more accurate to subtract a fixed number.

I was also told that a particular Factory 1 race boat striving for a kilo record used the standard Bravo drive because the horsepower loss was noticeably less than for a Bravo XR drive with straight-cut gears.

Re: HP losses from Bravo 1X drive
 

What you say sounds logical for just the "rolling" resistance of the gear box, and probably to wet sump "pumping" losses as well, but I don't believe it applies to losses at the gear teeth.

If you are spinning the input shaft at 5200 RPM with a 50 HP electric motor, then you are spinning the prop in air or spinning a very small prop, and there is next to no load on the propshaft. Under these conditions it will not take 30 HP to spin the drive since much of the loss comes from the gear teeth having to carry a load.

If you are spinning the engine at 5200 RPM with 1000 HP, then the prop is putting a huge load in the gears and the loss will be higher. And with 1000 HP you are definitely exceeding the design of the gear, so more deformation of the teeth under load, more contact area, more friction and higher percentage losses. A loss of 6+% or 60+ HP seems reasonable in this case.

The higher losses on the XR straight cut gears supports this argument. They are stronger due to more tooth contact area, but more contact means more area for friction to happen.

I admit to having reached the limit of my meager knowledge on this subject, and would appreciate a better explanation from someone who really knows this stuff. :D

Re: HP losses from Bravo 1X drive
 

Tomcat, you've got to be right about the increased frictional losses created by loading the gears. That means there will be variation in internal resistance based on how the gears are being loaded. Somewhere, someone has tested this!

Re: HP losses from Bravo 1X drive
 

In listening to the gear case GURUs I heard that
the XR gears are more ductile and tougher to better tolerate the higher torques where as the standard X gears are much harder and therefore also more brittle and less tollerant of higher torque loadings. In the end this I again have heard results in higher wear rate of the XR gears than the X gears wear because the XR gears are softer and the X gears are harder. Higher gear wear rate may (or may not) also be indicative to higher friction losses with the XR gears.

Re: HP losses from Bravo 1X drive
 

So why not measure the amount of HP required to turn a Bravo drive. Oh Yea you can't measure HP, So why not take a TORQUE wrench and measure how much TQ is required to turn over the drive. Synthetic lubes will lessen the TQ required and free up some HP. Who has a drive sitting around and can test this. Or you can test this in the boat in neutral and also in gear to see the added rotational requirements of the engine(the plugs need to be out and the throttle held wide open).

Re: HP losses from Bravo 1X drive
 

The difference between the X and the XR drive are the straight cut instead of bevelled gear teeth, and the 1 1/4" instead of 1" propshaft (and a few other features).
The straight cut gears can handle greater load because the contact point between the gears is flatter and therefore a larger effective surface. The disadvantage is more friction and more noise. I think 30 hp is about right for the XR and 15 - 20 hp for the X. An IMCO SC saps 50 - 60 hp but can handle 700+, as a comparison.

As far as the HP ratings of the Mercury power units go, I can only tell you what is written and what I have experienced.

When Tyler Crockett tested the stock 496HO before fitting CMI headers to it, he recorded 425 hp at the crankshaft, added the headers and saw 485 hp. Other dyno tests have also recorded the 425 hp at the crank. Raylar, for example. If the hp rated by Crocket had been propshaft, that would make a 496 w. CMI´s more powerful than a 500EFI, which it isn´t.

Mercury racing officially promotes its 525 with exactly that amount of propshaft horsepower. The picture taken at the Miami Boat Show this year shows that!
My own 25 Outlaw with the 496HO did 67 mph GPS maxed out on a good day. X drive, labbed bravo 25" @ 4900 rpm.
It now does over 80 mph GPS fitted with a 2006 525 and an IMCO 3" lift extension box. XR drive, labbed bravo 28" @ 5300 rpm.
Let 4 mph be the result of the ext box/ higher x. That´s still 9 mph due to the motor.
The effective horsepower difference between 496HO and 525EFi is about 115 hp.
I can´t explain the speed difference otherwise.

Re: HP losses from Bravo 1X drive
 

I was just looking in an old stern drive manual I have and it specifies:
1989: 7.4L: 330 crankshaft HP
1989: 454 Mag: 365 crankshaft HP
1990: 7.4L: 300 propshaft HP (Bravo One)
1990: 454 Mag: 360 propshaft HP (Bravo One)
1991: 7.4L: 300 propshaft HP (Bravo One)
1991: 454 Mag: 350 propshaft HP (Bravo One)

So why a loss of 30 HP on the 7.4l and only 5 HP on the 454 Mag in 1990 through a Bravo One drive ?
And then a loss of 30 HP on the 7.4l and only 15 HP on the 454 Mag in 1991 ?

I think Mercury Marines HP ratings are a little inconsistent, which makes it difficult to calculate the loss at WOT in the drive.

Re: HP losses from Bravo 1X drive
 

Someone please put a torque wrench on a drive and see how much to make it turn.

Re: HP losses from Bravo 1X drive
 

It would seem that the torque that you would record when the drive is just sitting there would be a lot less than the torque that would be required to turn the drive with the gears and bearings fully loaded when the engine is maxed out at WOT. Just a thought.

Re: HP losses from Bravo 1X drive
 

I have a boat I'm just completing. It has a pair of Whipple supercharged small blocks. I dynod both engines after completing them. I am going to put the prop shaft dyno on it next week and measure them again using a Bravo X drive. I should get a pretty good idea of what power is consumed. The engines made 570 HP at the flywheel. I'll be using the same dyno to prop shaft test them so It should be very accurate. I'll post the results.

Re: HP losses from Bravo 1X drive
 

Those numbers would be completely irrelevant!!!

The bearings are not acting hydro-dynamically at that point. If you look at the friction curve of any journal bearing system, it approximates a logarithmic function plus a constant: Very high at near zero speed, then approaching a lower constant as speed increases.

Re: HP losses from Bravo 1X drive
 

That will be very interesting! The way the dyno loads the outdrive gears (hopefully similiar to the way a prop would load them) we could also expect to see the logarithmic reduction of propshaft HP as you increase the RPM. Do you use the Land & Sea dyno?

Re: HP losses from Bravo 1X drive
 

Marty,if a drive is set up with the right bearing preload/rolling resistance the tq required to turn it sitting on stand even imcluding oil is less than 5 ft/lbs,closer to 2 or 3. Now I'm sure that under a load at 6000 rpm's it must go up drastically,Smitty

Re: HP losses from Bravo 1X drive
 

I agree with everything you said except there is less tooth contact on xr upper teeth vs std bravo upper teeth as only one tooth is in contact,its just much stronger due to tooth having a much thicker root strength,Smitty

Re: HP losses from Bravo 1X drive
 

I haven't compared a measured hp loss but I can tell you this summer when I was trying different surface finishes and treatments on lower bravo gears in my quest to find something that will extend there life I ran 75/140 royal purple and was never able to break 90 mph. At the end of the season in almost identical weather conditions/water temps I once again saw mid 92's after switching back to 75/90 royal purple. I am going to do more back to back testing in the spring/summer with heavy vs light oil to see if it was just a fluke or if there is really that much difference,Smitty

Re: HP losses from Bravo 1X drive
 

In my limited testing I don't feel std x or bravo gears are any harder than xr gears,they are all made from 8620 steel with a case hardness of around 60-61 rockwell. Some of the first xr pinion gears had accelerated wear due to improper heat treating but they generally wear faster due to fact only one tooth is in contact at any given time vs sevearl on a std bravo upper. As I mentioned earlier the one tooth has a base/root thickness 4-5 times thicker than a std upper tooth so it doesn't fail catastrophically under a highload.The final surface finish on the gears I'm having done for my customers is very smooth,almost like a mirror,and they don't seem to bite into each other as the teeth mesh together which will create less friction and longer life,Smitty

Re: HP losses from Bravo 1X drive
 

Yes, it's the L&S. I use the same absorber for prop shaft or engine stand.

Re: HP losses from Bravo 1X drive
 

Anything on Redline (heavy) shockproof gear lube?

Re: HP losses from Bravo 1X drive
 

I have a friend that drag races the 2.5's here and all he uses is the Alisyn oil. I used it type 2 in a Imco drive, it is a lot thinner than the merc stufff.I could spin the prop by hand like a fan blade.

Re: HP losses from Bravo 1X drive
 

Rob,
I have used Merc, RP, and Alisyn. Gear wear seems the same with all three, but the boat is faster with the synthetics.
I am using Alisyn engine oil too.
Who is your drag racing friend? I may know him.
Happy Holidays,
Steve

Re: HP losses from Bravo 1X drive
 

Dewitt and Daryl with Boat Works,Ridgeland Ms,boat name Dock Rocker.its a Traid .The Motec stuff they use is pretty cool.They started out with it on Alcohol with about 30%nitro,the last few year they did the 2 stage nitrous deal.Ive heard them talk about Steckbauer a pretty good bit.

here one of them :drink:

Re: HP losses from Bravo 1X drive
 

I know DeWitt well. Great guy, fast boats. Darryl Lane is one of the best motor builders in the business.
Does DeWitt still own the lake bar? That's a fun little hang out :drink: !
Regards,
Steve

Re: HP losses from Bravo 1X drive
 

Yea I grew up with them drag racing cars,The bar is close they sold the Marina.The sheriff dept pretty much put them out of biz with all the road blocks etc.

http://www.offshoreonly.com/forums/s...&highlight=dui

Re: HP losses from Bravo 1X drive
 

Have you tried the cryogenic gear treatment for wear?