They usually don't last long with big horsepower , over 600 HP

Teeth will pit/chunk out and if you're real lucky, you'll get one where a tooth breaks off and junks the whole thing out.

Just to help out the original poster. B1 and XR lower gears are basically the same. Both are near net forged also known as close net forged. Near net forging is a somewhat new gear manufacturing process. In a nut shell near net forging is powdered metal hot hammered into a gear shaped die. The advantage of near net forging is supposedly lower cost and reasonably good tolerances. Near net forged gear teeth are hard on the surface but still retain the original toughness of the chosen metal internally. Really the best of both worlds as you get a gear tooth that has some flexibility so it won’t just ‘snap off’ and a hard tooth face for better wear.

The upper driveshaft housing is where the B1 and XR gears differ. The grain structure of an XR and a B1 upper gear set are different. The B1 gears are helical cut billet gears that are heat treated. The B1 upper gears have more teeth with very good wear characteristics compared to the XR gears. The helical cut gears because of their thinner cross section usually won’t handle the additional horsepower and torque compared to an XR gear. The helical’s are just a tad more brittle. Usually on a well maintained outdrive you won’t see a helical cut gear (B1) wear out but, more often than not they suffer from a catastrophic failure or tooth fracture when their design limit is met.

Like in the first paragraph the XR upper gears are a straight tooth design. The XR gears have fewer but much thicker teeth than the helicals.. The gear faces I have observed generally have a Rockwell C hardness of around 59 to 63 depending on the batch. The hardness depth is in the .010 area. On this forum you will find XR drives coupled to all sorts of horsepower and boat weights. Once you exceed the design limits which in this case is around 550 hp then the wear factor on the gear faces abrade exponentially. When the hardness layer gets thin then it will start pitting or flake particles off its face. Game over

Mileage on a set of gears is a makeup of initial gear setup, horsepower or torque, maintenance and stick management.

Hope this helps and like I said your mileage will vary

So on the plus side, I have a light boat, 290 Velocity VR 1. On the minus side when the motor is done it will be around 600hp. What can I do extend the live of the XR? I always ran Royal Purple max gear in my Bravos and used a drive shower. Can the upper gears be replaced with better gears?

Padraig

You can have the gears Cryo treated.
Run Bravo Shop's Neo synthetic lube.

Thank you for all the info guys, it is much appreciated. Is the Neo synthetic the best Bravo gear lube out there? I had read about using a zero weight synthetic from Torco?

Look at Hydraulic steering instead of the XR.