MikeStar

What's the difference between the XZ drive and the XR? I've seen a couple of boats lately (notably, a 2002 31 Sonic with HP500 EFI's) that are using the XZ drive. I've only heard the board talk about the XR's, so why are folks using the XZ's, and is there any advantage to one or the other?

Or is this just Merc's way of confusing an already confused issue??

HavasuCat

xr's run straight cut gears and the xz does not. I know the xz will run a little faster, but the xr will take more hp before it breaks. When DCB was testing their new 34 cat they switched from xr's to xz's running the same Teague 620's and picked up I think 6 mph top end.

Dock Holiday

Mike, I was confused as well. Ordered a new boat with 500's and they told me it would come with XZ drives. I thought they were making a mistake and really meant XR, until a good OSO member gave me the following link.

Check it out.

Here is a page that describes the changes in the new drives.
http://www.outdrives.com/bravo2000.html

Because I have no plans at all to add blowers, I think I will be very happy with the XZ units.

Mark

Mbam

I have a table at

Bravo Drives

That summarizes the differances.

MikeStar

I have to wonder if the only difference is the gears, and neither drive is rated for more than 500 / 550 hp, is it really worth it for Merc to build two different drives? Seems like 90% of the manufacturers are using the XR's anyhow... unless the XZ is really more for the lighter boats, since boat weight also affects the amount of stress on the drive? Maybe XZ's make more sense for singles and small twins, XR's for the larger, heavier boats? Speaking stock, of course.

I heard a rumor a while back from a friend in the industry that Merc was working on a drive that would bridge the gap between the Bravo's and the #6, maybe good to 650-700 hp or so. Wonder whatever became of that project?

Cattitude

The only difference is said to be the upper gearset. forged, machined and helical on the ZX and forged, as forged finish and straight cut on the XR's. Initially the XR was only available with 1.5 ratio.

Ultimately you could run an XZ and if you have problems with the gears change them to XR gears down the road.

Mike "Goodfella" at Dollar had reported last year that the factory racers his shop was involved with were getting better life out of the XZ gears which was not expected.

As an engineer, I've got two theories-

1- the machined ZX gears likely have better tolerance control and surface finish on the gear teeth

2- Helical teeth serve to pump oil thru them where the straight teeth simply squeeze the stuff out of the oil.

It would also be interesting to compare the surface are of the contact pattern on the two sets. On helical gears there is also more of an opportunity for a smooth transition of the load from one tooth to the next where a straight gear has more of a stutter transition- think of driving a car with stop signs for wheels. I suspect you can't really see or feel this but it is there theoretically. There is a reason auto's use helical gears in the ring and pinion as well as forwrd tranny gears (Whiny reverse gears are most often straigh cut gears)

I upgraded to an XZ simply because I found a great deal on one over the winter. If and when it cooks I'll take what I've learned on the board and select my next gearset to go in.

denohew

Take it from me, Don't buy either one. They are junk!!! denohew ( Luna Sea )

Cattitude

Denohew,
without a doubt you've been through an outdrive hell that no one deserves and I am certain of your good intentions to warn others to avoid the same fate.

In reality though, the XZ and XR drives have proven to be significant improvements and are a worthy upgrade for many pleased owner/operators.

sadly, Merc and /or Nortech (Whoever ultimately decided to use the merc package to propell your beautiful but very large Nortech)dropped the ball when considering the entire package.

My father had a similar misfortune with a 29', 10' beam heavy commercial fishing boat. The builder opted to power it with a single volvo DPX Duoprop and Volvo turbo diesel package (bone stock). When running it performed well and was extremely efficient. But with six blades in the water, a heavy long boat with considerable wetted surface area, 1000 pds of fish on a good day, 7-8 fisherman, food, coolers, it spit out about 2 drives a year. dad was replacing them with factory new, Volvo warrantied a few, but the expense and nuisance factor was exhausting. Ultimately dad sold the boat, with a new drive to a "hobby" fisherman who would not have the weight issues or the hours Dad logged.

My point is that any drive can fail and application is key. The XZ and XR offer considerable gains in reliability for the majority of the sport boat enthusiasts on this forum. Those with heavier boats (28-30' singles or 35+' twins) and more than say 500 HP/500 ftlbs may want to consider better alternatives. That is only my estimation based on following the board. People talk HP but it's actually the torque , props and boat you are trying to push with it that kill the drive.

If the motors are putting out, a heavy boat is resisting forward motion, the props are "biting" something in the middle will be the fuse.

Personally, the XZ has been a wonderful upgrade for my 25' Daytona combined with an Imco shorty- I've messed with setup only and found 11 mph.

BAJA WILL

My take on XZ, I purchased a 2001 500efi came with XZ, at 50 hrs the upper crunched 8 days before warrenty ran out, Merc did replace upper and covered labor but was a ***** I had to get Fountain involved to even get merc to answer the phone. And in the end Fountain ended up having to give me a seal kit to get me back on water brofore the summer was over, merc could have cared less.

My take, I hope I never have another failure, but if I do, I will be switching to the IMCO, and give them a try.

Another note, because of that one failure I have not Whippeled my motor, if it failed under 500hp I am sure it will at 600-700hp.



WILL

WILDTHING TAZ

I HAVE BEEN FOOLING AROUND WITH DRIVES FOR 2 YEARS. I THOUGHT IMCO,TEAUGE,AND ALL THE HP DRIVE BUILDERS WERE DOING SOMETHING TO HELP THE PROBLEM.TRUST ME WHEN I SAY FOR THE MOST PART (THEIR NOT!!). EVERY ONE OF THEM ARE USING MERCURY UPPER GEAR SETS. THEY MAY BE WELDING THE FLOOR PLATES,SHOT PEANING GEARS,OR REPRODUCING THE SHAFTS USING DIFFERENT MATERIAL. BUT STILL USING THE SAME FRICTION WELDED TOP GEAR SET FROM MERC. MOST OF THEIR IDEAS MAY HELP THE 7500 LB BOAT LIVE A LITTLE LONGER.BUT HAVE NOT IMPROVED THE BRAVO OUTHER THAN THE PRICE THEY HANG ON IT,AND THE BULL**** THEY FEED YOU IN THEIR ADDS. NO ONE GIVES ANY WARRANTY ON PARTS. THINK ABOUT IT THE BRAVO MAKES MERCURY A **** LOAD OF MONEY,WHY WOULD THEY CHANGE ANYTHING?THE SMALL AMOUNT OF US THAT NEED A STRONGER DRIVE IS NOT ENOUGH FOR THEM TO MAKE A CHANGE IN THE BRAVO TO WITHSTAND WHAT WE NEED.THATS WHY I WENT TO THE B-MAX. AT LEAST DEAN WENT THE EXTRA STEP AND SPENT HIS MONEY TO MAKE IT WORK!I HAVE TRIED THEM ALL.ADVERTIZING & BULL**** SELLS, AND WE PAY FOR IT. WILDTHING