Been getting into watching Boostpower TV on youtube, thought I would pass this on. Alexi Sahagan seems to prfer helical cut diesel bravo gears, he mentions that XR gears can be strong if set up correctly with deep engagement, but the helical gears have approximately 2.5 tooth contact patch. Have a watch...

https://www.youtube.com/watch?v=ZFgOVmCqwRA&t=369s

Now with the helical cut gears , you create axial force and put more stress on the case and bearings etc ...now you've moved the failure further down the chain . The boys at Mercury are pretty sharp and I figure they have thought about this and played with it . It's the reason after 3 failures with my Bravo based SC drive , I upgraded to an SCX , it's just bigger all through .

I have 100 hours on my bravo xz gears (helical cut) behind 700 then 750 horsepower in a Checkmate 253. Just had the drive tore down and gears are in good condition. Can probably get another 100 hours out of them.

XZ gears did hold up really well. Unfortunately, they no longer make the XZ drive, so usually you have to find a dealer that has a box or 2 on the shelf. The production of these gears for the years they were made were really good whoever was doing the work for mercury. Mercury sometimes changes vendors and quality becomes an issue. Had the same problem years ago with TRS gears. The original ones that mercury produced when the drives were current were great and held up, then the drives were being discontinued and the gears they were making after that were junk and didn't last, they probably sourced them to low bid because they weren't making the drives any more.

I have some real world experience with this. When I put the 525 in my Donzi 22 Classic I blew up the Bravo X upper with the helical gears in 5 hours. My replacement XR upper lasted a couple seasons until the bearing preload nut backed off and took it out. My second XR upper has lasted about 5 seasons so far. Sometimes what works on paper does not correlate with reality. XR is definitely stronger.

I subscribed to this YouTube channel. Better link to video below. ⬇ The Bravo talk starts about 15:10.

https://www.youtube.com/watch?v=ZFgOVmCqwRA&t=402s

Which is considered to be the stronger drive XR or XZ or is it all preference ?? being in stock form not modified

XR is stronger.

XR are stronger....XZ are faster.

Just a fact in Gear Geometry. Straight Cut versus Helical.

Like I said I had a 2001 Checkmate with XZ on it, and gears always looked brand new. It was stout when Mercury was actually selling the drives.

We had a lot of good success with Bravo XZ drives for many years on our 32 Active Thunder with N/A 700's. In 8 seasons, we broke one set of uppers. We do all of our boating on Lake Michigan... so that's a lot of prop loading/unloading.

My undoing was the XZ lowers (same as XR lower)... the original gears were great, the replacement gears (several sets) we generally couldn't even break in with a OSO reputable installer doing the setup (by the book). We finally flipped the original set of gears around that lasted a long time and the reliability came back... frustrating.

Technically the XR gears will endure shock loads better than the helical XZ gears, but they don't wear like XR straight cut gears... so if you can take it easy on them... they have lasted much longer than XR's for some applications. I also think the size and weight of the boat vs. power has to be considered... our success with a 32 A/T might not be possible with a 38 Top Gun with the same engines.

I've heard if you have similar horsepower with blown engines, the torque will crush those gears much faster.

As far as not being able to get XZ gears, I believe the X upper is basically the XZ upper and I'm sure the XR and XZ lower are the same. The X lower has the smaller prop shaft and bravo 1 lower gears