Drive/HP question
 

I bought a 28 foot donzi ZX several years ago. The original engine was a merc block 502 mag w/ 415hp. I've outgrown the power and decided to beef up the engine. The engine now has 575hp(N/A) at the crank. My first question is, should the Bravo I drive be able to handle the extra hp? Secondly, what percent speed increase should I expect(roughly)? I was running 55mph before. I think the boat weighs 4900lbs dry.
Thanks for the advice!

JP

No, the drive won't hold up. It will fail and you will ruin a weekend of boating for sure.

The best thing you can do is go out and buy the newest, strongest Bravo drive (XZ?) and hope that it stays together.

I would wait for the 2004 sterndrives to be introduced to the public before upgrading though. Maybe there will be something stronger than the XZ in Mercruisers future plans.

See if you can find a local Mercruiser mechanic who is attending Mercruiser service school this winter (most attend every other year) and ask him his impressions of the new products. After he finishes the school he will be knowledgeable on the new product upgrades and can advise you accordingly.

Dennis Moore

Torque is what is going to blow an outdrive apart not HP. Your drive may hold together depending on your driving style. If you are pounding on the drive in the peak of your torque curve I would give it a 50/50 survival chance. WOT won't blow this drive apart so if you are gentle getting there you should be ok. Put a drive shower on it and use synthetic gear lube until you can get a new drive or find someone who can do a beefier rebuild on your current drive. You might also want to consider a prop with a rubber hub.

I agree, it depends on how you drive it. I have a friend with a 28' boat, 5300lbs. Does 91 on radar with a stock Bravo I drive. He treats it right and it returns the favor. He ran it four years with the big motor before we tore it down. I replaced all bearings and lower gears and it is still running this year so far. Everyone believes it will break and it will, but he has gotten his money's worth from that drive so far. If you are easy on take off and dont fly wave to wave, and it is in good shape to begin with, there is no reason that it wont last for a while. You can upgrade to X gears or XR gears for a better chance if you want. If you have any questions pm me we can chat..

Dick

Doc,
I'm no expert, but I can tell you that I have run 454 blower motors (approx 525HP) through bravo 1's and they held up just fine. Not a single problem with them.
Dean

The boat Mr. Gadgets is speaking of has a naturally aspirated 588 cubic inch engine making very close to 800hp.

Thanks Guys..I really appreciate the advice. Does anyone have a guess on what my new top end might be? I was thinking 70 mph??

I owned a baja with 650-700 hp for 10 years & never tore the outdrive up. It was the orginal version 1 of the bravo. I never worried about it comming apart.

Try this link to answer your speed question.
http://go-fast.com/boat_speed_predictions.htm
JB

If you added 150hp, you will most likely gain from 8-10mph.
As far as the drive, I have 5200lb dry weight 28 Pantera with a 525SC. I blew the stock Bravo upper apart at 205 hrs. I now have an Imco extreme advantage(non SC) with a stock bravo lower and have not had any problems in 125 hrs. I baby it coming on plane and the prop only seldomly comes out of the water.