That chart that rbtnt linked to, tells it better than my memory can hold it.. Although you can mix and match just about anything.. best bet is to count teeth.. You never know what someone before you have done to build it.
It does look like they had a differnt upper gear set to make up the 1.36 XZ. With the XR there is only one upper set, 16/19, so the drive ratio is set with lower gears in the XR.

From that chart it looks like the XZ could be built either way, but I am assuming this chart follows the Merc chart and it is correct. I do know that the 1.36 upper gears are more expensive than th 1.5, same with the lowers.

Hope this helps..

D*ck

I guess I don't understand this chart. It says the XR upper is 1.50, but the gear set is 19/16. 19/16=1.19.

I do see where the total ratio comes from:

19/16 x 19/15 = 1.504

Michael

From what I have be told and I have XZ's on my boat, they are geared different in the top, not the lower.

Michael,
The over all gear ratio is a product of the upper and lower sets of gears. Merc only makes the one upper gear set for the XR, which combined with lower set can produce 1.5, 1.36, and a 1.25 gear ratio.
The helical cut gears can be had in a 1.5 and 1.36 and think one other (slips my mind what it is) upper set, then you combine the lower gears to get the end ratio. Now mind you the helical cut gears are also a product of the combination of upper and lower gears. I generally work with 1.5 and 1.36 and mostly XR. I do have some old sets of helical cut 1.36 gears. I generally just dismantle the drive to verify what is in the drive and replace as necessary..
Merc has a chart that explains is a little better with part numbers.
http://www.mercruiserparts.com/Show_...28XR+%26+XZ%29

This may confuse you more or help explain the mess.. there is another chart for the older and newer B1's. But the end result is the upper and lower gear sets produce the final ratio, but it can be done in a couple of differnt ways..
Hope this help..