I have 2 almost new Bravo one with 1.50 ratios. I am currently running 454's but am thinking of upgrading to some 500's in the near future. At first I thought I would paint up my outdrives and try to sell them but then I saw an add on here where they can upgrade your drives for like $3500/drive. Has anyone every done these upgrades or is it just a cheap alternative that won't last long.

You shouldn't have any real issues with standard bravo's and 500hp's. The XR's will also be 1-2mph slower than regular Bravo's. The gears in XR's are stronger, but they also don't last as long under normal use.

Don't waste your money .

The internals are the same from the B1 to the XR except the input gear and input shaft they have larger splines and ujoints in the xr's. The xr has a sleeker housing and 1 new ratio, and a new sticker price. If you are running stock power even 500's the B1 will be fine for most boats under 9-10K lbs.

If driven with some normalcy and no 5 blade props.

The B1 has helical cut gears in the upper. If you dont have enough power to knock the teeth off, you are better off with them, than the straight cut, net forged, XR upper gears.
Upgrades to thick floored helical cut upper gears was done when the serial numbers started with OM and after. The B1 X has a steel tower in the upper case.
Older B1's can be upgraded with the thick floored "X" gears and steel tower and XR ribbed top cap. Properly setup they have been holding up well in higher hp applications.
For 500hp the older drives weak point ( OL and older) was the thin floored gears. The floor of the gear would break out and you were done. It normally doesn't destroy the case, but the tower alignment and shape needs to be checked anytime gears fail in the upper.

Hope that helps.
Dick

What about 525s how would the B1 do ?

Interesting thread. I'll eventually have to consider options for my old B1's if I bump up my 540 Bulldogs. I thought XR's might be an option, but maybe I could just beef up my B1's?

I think the key is to do the upgrade BEFORE it breaks

Would Bravo 1X drives handle 650 hp in a 34' v hull - twin engine application??

Not good. Mine lasted about 40 hours.