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.