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Originally Posted by hadleycat
(Post 4436296)
I am running 750 thru an Bravo XZ rebuilt by Mr. Gadgets on a 25 Checkmate with about 70 hours so far. I am easy on the hole shots and try to keep it in the water. If you drive it like you stole I am sure it wouldn't last long. I believe people are having better luck with the XZ drive lately because the new XR gears are not as durable as the old ones. On one of the recent episodes of Boost Power TV Alexi talks about the XZ drive versus the XR drive.
Here is that YouTube - its makes sense. |
I believe torque vs load is what wears gears. boat weight per drive vs torque input.
3000 lb boat with 600 ft lbs input trq = 5-1 weight/trq ratio. 6000 lb boat with 600 ft lbs input trq = 10-1 weight/trq ratio. 15,000 lb boat w/twin drive /2 = 7500 per drive with 600 ft lbs input trq = 12.5 - 1 weight/trq ratio. My thought is 12.5 - 1 is the upper end for any bravo drive to exceed 100 hrs operation. several variables to this but rough way to calculate the load on gear set. Merc only offered the heli cut gears for years behind diesel engines. I think the swept back Bravo X with finned cap and XR lower is the best Bravo. The above video is right on track. The other way to look at it is the new heli gears are half the price of straight. two sets of heli gears will last longer than one set of straight. The bravo case size is becomes the limiting factor. You can only get so much gear size in the case. That is why the BMAX and SCX drives have a bigger upper case to install larger upper heli cut upper gears. Note the lower gear set is still straight cut merc gears on both drives. |
Many use Merc HP Gear Lube.
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Originally Posted by 28ftsportcat
(Post 4438857)
What gear oil should i run for over horsepowered xr drive trying to prolong it. been running just merc quicksilver but went up in hp this year
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Originally Posted by Wilks
(Post 4438870)
I believe torque vs load is what wears gears. boat weight per drive vs torque input.
3000 lb boat with 600 ft lbs input trq = 5-1 weight/trq ratio. 6000 lb boat with 600 ft lbs input trq = 10-1 weight/trq ratio. 15,000 lb boat w/twin drive /2 = 7500 per drive with 600 ft lbs input trq = 12.5 - 1 weight/trq ratio. My thought is 12.5 - 1 is the upper end for any bravo drive to exceed 100 hrs operation. several variables to this but rough way to calculate the load on gear set. Merc only offered the heli cut gears for years behind diesel engines. I think the swept back Bravo X with finned cap and XR lower is the best Bravo. The above video is right on track. The other way to look at it is the new heli gears are half the price of straight. two sets of heli gears will last longer than one set of straight. The bravo case size is becomes the limiting factor. You can only get so much gear size in the case. That is why the BMAX and SCX drives have a bigger upper case to install larger upper heli cut upper gears. Note the lower gear set is still straight cut merc gears on both drives. I.e. 6000 lbs boat / 600 ft lbs = 10/1 6000 lbs boat / 300 ft lbs = 20/1 You say 12/1 is the upper end. To me it looks like the 20/1 is a better number because it has less torque. Where as 10/1 has not only same weight but higher torque. I would argue that drive will not live long |
Originally Posted by 28ftsportcat
(Post 4438857)
What gear oil should i run for over horsepowered xr drive trying to prolong it. been running just merc quicksilver but went up in hp this year
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Originally Posted by 28ftsportcat
(Post 4436210)
How much hp can a xr drive handle with 1.5 gears
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Originally Posted by hadleycat
(Post 4439490)
Amsoil Severe Gear
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Amsoil Severe Gear here for all my HP customers and my own!
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no gear lube in this world will save a bravo style drive in a heavy over powered boat.merc put them behind up to 600 hp but they are ticking time bombs just waiting to explode.
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