Stern Drive Upgrade
 

Hello everyone,

I'm new here and so thanks in advance for your guidance/input

I'm considering the purchase of an older Donzi 38ZX w/twin 525 SC Mercruiser engines (all original) and Bravo 1 drives (also original). And so I'm thinking I'll need to go into the heads and replace valve springs and do a valve job, etc., to freshen up the top end, which will make me want to increase the boost a bit when finished, in order to develop more torque & hp. As such, I'm wondering if it's a good idea to do some upgrades on these drives (which likely need going through anyway due to age & wear) or should I just sell them outright and upgrade to new XR drives, B-Max drives, or something else to enhance reliability, efficiency, etc.

My thoughts are that if I'm putting out 600+hp after the refresh work, I may be pushing these drives to their limits and eventual destruction. I'll be gentle with them, but wholly believe in utilizing equipment with reserve capacity, i.e., drives made for more than I need e.g., 800/hp and torque. If they're over-rated and under-utilized, they should last quite a bit longer...

Any thoughts?

Thank you!

This question is eventually asked by everyone with Bravo drives over 500 hp. These are many threads on this.

In my opinion you need to look into Imco's as the best balance between money spent and reliability, Others strengthen the bravo drive system, Imco uses larger gears.

Thanks for the info Apex. I will def look into the Imco drives.

If you plan to keep the boat for a while, I'd go with Imco SCX uppers and Imco SC lowers with 600 HP. You probably could get away with XR's at 600 HP, but that even puts XR's on the edge. Put the above mentioned package on and you will have a trouble free setup. As important in my mind is that you will most likely go up in HP at some point and the SCX's can handle up to 900+ HP. There have been a few used SCX's for sale, so you may get a deal if you're patient. Good luck!

IMO theres no point buying a offshore boat to drive it like a grandma. But unfortuantly we all have been there at some point. Looking back i would rather have less power and speed but drive the boat like shes made to be driven!

Budget wise build 500HP and just enjoy the boat freshening your bravo drives to OE specs.

If your set on more power but still on a budget the best bet is to buy a spare matching drive or two and rotate them thru when they wear out, rebuilding in the off season. ANY bravo based upgrade that does not have larger gears are a waste of money.

If you want to do it right install full imco SCX upper and lower drives.

With the B-1's on it you probably dont have HP gimbles, If the budget will support it, Id put HP Merc or IMCO gimbles on it with swep back XR's and IMCO shorties, JMO good luck, a pair of new SCX's are about 50K

Lots of options. Some much more expensive than others. If you plan on driving it hard or more power in the future, then upgrades to the Bravo's are a stop gap measure, with likely short maintenance intervals. There are Bravo's out there living under extreme conditions. But there are also a lot more of them that will fail.
In my opinion, the best bang for the buck is a full SCX, Upper and lower combo. They have bigger gears and solid parts, and have been holding up in a lot of situations. Over kill for your 600hp, yes, but margin has it's place in life. To bolt on a set of SCX's, you would need the SCX helmets and reservoirs. While you are there, add some safety and install the Imco Gimbal rings. List price on the drives, gimbals, helmets, reservoirs and shipping is about $40k. They can be had for less every day!
If it costs $3500-$5000 for each bravo break (being conservative) that is about 11 1/2 to 8 drives for the money. Now if you can schedule the bravo breakage at the end of the season, that would be good.
If you want to run it like you stole it, well, the SCX is a pretty durable package. And you could look at power upgrades down the road if you wanted.

If you have good luck with XR's then it is not a bad way to go. You only know how good your luck is, when they don't break. The price on XR upper gear sets is equivalent to their weight in gold these days.

Just so many ways to look at this. I fix and modify bravos, but would rather sell SCX's. I have one on my boat, and I seldom worry about the drive failing.. Piece of mind is priceless!!

Hope that view helps.
Dick

I have stock 525sc... my plan to freshen the top is Edelbrock rpm heads, shave 020.-.040 to bump CR to 8:1.Forget raising boost you will make out way better.by upping CR a little,with edelbrock aluminum heads

I'm not needing more than the 25+hp and 100 pounds weight savings it would give.Not into breaking drives.
Oh my 1997 525sc has HP gimbals stock BTW.

[QUOTE=Donzi38ZX525SC;4249875]

My thoughts are that if I'm putting out 600+hp after the refresh work, I may be pushing these drives to their limits and eventual destruction. I'll be gentle with them... boy that sounds a lot like "I'll still respect you in the morning"!!!

that 38 doesnt run half bad with 525sc's. Stock that motor is pretty solid.

Your looking at some things...

1. you want to freshen the heads and crank the boost. thats a 177 blower, spinning the hell out of it is not the answer, you will just start making heat. So now your looking at roller cams and valvetrains x2 and better heads x2 though the low comp on the 525sc comes from the pistons so now your into the bottom end....

2. Now that you dropped a good chunk of change on the motors you get the drive issues.


3. this leaves you with either spending buckets of duckets to do it right or just swapping pulleys and puckering every time you hit it.

or putting those 10s of thousands of dollars in the gas tank and enjoying what you have for what it is.

Thanks TCBoss302. I can see that the SCX drives are definitely the way to go reliability-wise. And it's great now that I have an idea of what they cost. Wow. Pricey @ $50K for a pair. Since I'm not going to be running in salt, but rather in lakes and rivers, I'm leaning towards either XR's or upgrading the Bravo Ones. I guess it boils down to value. If I can achieve considerably more strength with one VS the other...Wow am I learning a lot here. Very thankful...

Thanks Dick.
I'm leaning towards the XR's at this point. Until then, I guess I need to get used to the boat the way it is and when the 100/hp-itis sets in, then I'l need to give serious consideration to the SCX upgrade. Lots to think about. Reliability, performance, fun.

That sounds goo MichiMike. If I do end up pulling the heads, it only makes sense to put the engines in a diet and drop 100# a piece. I'm assuming the Edelbrock heads have nice large rectangular ports big enough to stick your fist into. Cramming more air into the power plant is always a good thing...

Haha. Made me lol. Yes, I'll be gentle for a while, then I'll need to hear those big blocks sing to one another...

You make very good points phragle. Thanks for the perspective. I didn't even think about the extra heat issue with the superchargers. Thinkin' I'm gonna just get everything in good shape, and go from there. If the heads need to come off, I'll err on the side of reliability over more power. Then, run it for a season, and see what I think about it after that. At the end of the season, I'll have a better pulse for how it behaves and decide what's next.

$50k for SCX's seems high, I was under the impression it can be done for $30-$35k all in. Am I wrong?

Fully agree, I had nothing but problems with the SC lowers since they still had the Mercury gears. I went through a period where I couldn't even get a new set of gears broken in running no more than 3500 rpms and babying the boat... never even took the boat offshore. If I'm not mistaken, there is still no true aftermarket solution for this. Many have tried annealing and re-heat treating, cryo, nitride coatings, etc... you might get a little extra time, but nothing that ever stopped the original problems from happening. Full SCX drives - all IMCO sourced gears - amazing how much better it feels to just go boating and not worry anymore.

50k is really high, I'm sure Mr. Gadgets can help you get a much better price - or try to find drives used in the classifieds.

Awesome info everyone. Thank you for taking the time to reply with thoughtful insight. Now I know what I gotta do eventually and planning for it. SCX x2.

The Edelbrock heads are ok, but it is closer to stock than some top of the line put your fist in heads.One has to remember your working with 177 blowers.In my case i really don't care about making much more than stock HP so this would do nice with stock cam/pistons.At 240 hours all I need is the blowers serviced now but next year a set of heads/head studs is in order.

I never knew what the others cost but if they are in that range for just the upper/lower then I'm way to cheap. :D

I agree full SCX/SCX and no worries or babying it anymore. I think that price quoted is including the transom assembly's. I had the HP transom assembly and just used the IMCO helmet not sure if you can do that with the B 1 but that would offer some savings

Yeah if your going to upgrade full trans Assembly's, gimbals, helmets, and scx drives your better off with the Arneson Bravo conversion asd7m. Best overall bang for the buck.

Your right I talk to imco and $30-$35k is about right for the setup.

I agree

if its 35K for two imco upper/lowers then the anresons seem like a hell of a deal

I agree

i dont understand this. everyone is saying the arnesons are to expensive yet essentially the legs of the imcos that everyone says slows them down but they still love them cost nearly as much as the complete arneson kit? how much more $$ is the transom assemblies, standoff box and steering for the imco's? looks like imcos cost blows way past arnesons price

Take the B1's off and send to bravo shop for overhaul first. B1 gear sets are less than XR's and B1's can live if driven correctly. Bravo shop has a platinum upgrade which installs bigger upper bearings and better upper drive shaft. they will also hard shim to get rid of slop that causes gears to fail. Add some of the synthetic gear lube they offer. Best update to the 525sc is a 250 supercharger and crane 731 hyd roller cam, lifters, springs. Will make 600 hp reliable and drive-able on 6 lbs boost and 91 octane. The 731 cam sounds great. 30-31p Labbed Bravo 1 props from BBlades. Boat will run in the 80's all day and ride like a Cadillac.

I have a 2001 with 575's in the same boat with xr's.

How much money is the Bravo Shop asking for this upgrade? A lot of guys run in the 500-575hp range with stock B1's without issues for long periods of time. I think you have the right idea if the horsepower is in that range. I just wouldn't spend very much money to upgrade a B1 when you can just get another one for the cost of some of the upgrades. Case upgrades make a lot of sense because it holds the gears and shafts in position. That said, Bravo I gears are Bravo I gears, the teeth won't handle going in and out of rough water on a consistent basis. If your power is conservative, and you are easy with the throttles, you do have a chance to hold up for a while.

Even upgrading to running the XZ/XR case doesn't fix the fact that the gears are junk. So if the Bravo Shop is making the even smaller gears live in a Bravo I case, they have the golden ticket. Can't tell you how many guys I've seen sit out a weekend of boating because of a drive with "upgrades" broke gears. In my experience, a twisted shaft is preventable (shock loads/bad throttling/hard acceleration) - more often the gear teeth will be gone before that. In fact, a little shaft twist is preferable to all of the shock transmitting into the gears. I never spent money on better shafts and never twisted one over many years with near 700hp. For the cost of highly upgraded XR/XZ drives, you can usually have a spare or 2 ready in the back of the truck.

When it comes to uppers, I personally think the Helical gears of the Bravo I,X, and XZ drives have long lives if driven well. The straight cut AND expensive upper gears on XR gears are a little stronger, but they need to be replaced more often because of the nature of a straight cut tooth wearing itself down because it's less efficient than a helical gear. I ran XZ uppers with great success for several years behind 700hp engines and did it with most of the hours in Lake Michigan. As I've mentioned before, the lower gears (XR - straight cut), were great until I changed from the ones that came with the drives and switched to new ones. I often couldn't even get the gears to live with Inland lake only - 3500 max rpm - babying the throttle break-in's. I never broke a lower gear, but I watched the magnets like a hawk and was seeing the gears pitting/flaking even during the break-in process. Tried many of the top gear lubes... same results everytime.

The only variable that changed was the gears being replaced from older parts to newer parts (same setup, lash, rolling torque, same 4 blade props, etc...). Mercury sold good gears up to the early to mid 2000's and went to Chinesium later on. A lot of guys have sent them to labs and no one knows exactly what alloy they are... not a good sign. 8620/4340 are great materials when forged and case hardened... I doubt Mercury was reinventing new alloys, but rather just accepting whatever gear from their Chinese vendor got them to a minimal acceptance threshold. I got well over 300 hours out of my first 2 XZ drives without problems. Then I change lower gears. Since their newer gears can JUST live up to 500hp engines (sometimes), people will keep buying more sets that won't be warrantied. Why would Mercury change? - great money-maker. Nothing like that feeling of checking the magnets after a ride wondering if you're pulling the prop shaft out or going boating tomorrow - seemed like it was a 50:50 chance either way.

Long story short, if you buy any Bravo drive, be prepared to calculate how many failures it will take to buy an Arneson, SCX, SCX4, etc...

I don't understand putting up with bravo drives on this type of boat? It's 15 k for both the upper and
lower SCX and no more driving your performance boat like it's made of glass. Doesn't take very many rebuilds to pay for this especially to you put a value on not breaking down in the middle of the season.

Boatless -

My understanding of IMCO over Arneson is IMCO is an easy replacement to a Bravo drive, mostly plug and play, costs less and the props sits closer to the transom for those who do some family boating. I think modifying a Bravo style boat to Arneson style requires transmissions, possibly moving the motors, etc.

Can someone confirm the this?

In my scenario, I already was using IMCO extension boxes (not required with SCX) and HP transom assemblies with my XZ drives. My hydraulic steering was also configured such that all I needed to do was use one of their standard upper covers (had the necessary tie bar and steering ram flange for my system).

So I bought the SCX drives, helmets, and reservoirs. They came with the 1-7/16" hub to standard prop adapter. In my scenario, SCX drives was easily my least expensive step to getting a reliable boat. The drives are a little longer than Bravo I's as far as hanging off the boat. With my extension boxes and SCX drives, the Arneson ASD7M only would protrude a few more inches. That said, extension boxes are not required with SCX drives.

So basically, anyone that has the HP transom assembly already, just needs to swap helmets, make their hydraulic steering work with the IMCO cap (in my case, this was easy) buy the drives and reservoirs. For added safety, buying an upgraded gimbal ring would be a good plan as well.

The beauty of the SCX drive is that you can mount it up and go boating with your normal props. How fast you go may very well depend on how good of a match your X-dimension and props are to your hull. The Arneson drive offers the potential for a big jump in efficiency/speed along with similar or even better reliability because of the simplicity. Assuming your hull works with Arnesons (most do), your potential with Arnesons over SCX is incredible.

A lot of people I've talked to say that the Arneson drives do often require changing the angle of the engine. This angle change may slightly make it seem like the engine is moving forward, but not much. In my boat's case, I would need to change my offshore motor mount brackets (I will work with the ones I have) about 3 degrees - completely dependent on your transom angle. You may also need to drop the back of the engine down a little. The angle change usually means the front of the engine goes up a bit. In order to hit the same exhaust holes in my transom, I would need to cut my tailpipes (double-wall CMI), re-angle and shorten one of the legs, then re-weld together. This service can be done by Tig shops or obviously through any tail pipe vendor. Boats without transom or thru-hull water pickups need to add those for the engine cooling (mine already has this). The only other change I can think of is possibly needing to change a swim platform position if it interferes with the ASD7M box (mine most likely does). From there, you locate your ASD extension box based on a template, enlarge a hole in the transom for room for the transmission. The transmission utilizes the larger transom hole and large extension box to avoid pushing your engines forward like a TRS boat. From there, just bolt everything up. The rear motor mount is slick - it works with the transmission and drive attachment to lock it in (no back bolts needed like a Bravo). The ASD box is also really slick, steering attachment and plumbing, trim attachment, trim indicator, and trim plumbing all go through the box, so this cleans up the transom. The hydraulic steering rams are a different angle than typical Bravo's, so the orbital valve up front changes, this valve is included in the kit. This is what my Active Thunder with a 13 degree transom would require, other boats may be easier. That said, for the efficiency and simplicity of an Arneson system - once it's installed, this extra work seems very worth it.

Very well explained...

Not to mention the significant increase in resale, plus the stock POS bravo can be sold to help offset the drive upgrade expense...