baronbob

I have a heavy Cruiser (9000#s) with a converted 7.4MPI. Mag inners, Merlin heads, Gill exhaust and a 5PSI Procharger (just about ready to run her). The factory says a stock Mag will develop 560HP with the 5PSI pulley. The boat , last year, did 46MPH with the stock 7.4MPI 26" cupped props (4600RPM) and a stern jack. I have a drive shower on what I believe to be a higher geared otherwise stock 1998 Bravo III. Anybody have experience with high HP on a stock Bravo III. I know their are other upper gear-sets with bigger universal joints but I do not know if these are compatible with my stern jack.

nocigarette

im not a pro like most of the guys on this site. There are people on here that know anything and everything......But i can give you my opinion....The amount of weight you are pushing is going to destroy that drive with the hoarse power you have, i dont even think if you ease it on plane it is going to last on top end at wot......evrybody is in search of that faster top end so i imagine you are too. But you never know i would have another boat following me with a strong rope aboard............

GOODT

Ive never seen it hooked up to more the 425 hp, if going higher then that go with the new bravo 3 X drive

formula31

Is this a 9000 lb boat with a single? I would wonder if any Bravo is going to handle much power in that setup.

GOODT

had a customer last year with a doral that was about that heavy with twin bravo III went through 3 drives onthe third we got merc to upgrade him to bravo 3 x drives didnt have any more problems

Mudball

Assuming single engine:
If you are running the 7.4MPI otherwise stock internally with the procharger, then I think you have two potential grenade items....

I would expect an exhaust valve to end your engines life soon, unless you had the computer correctly reprogrammed, which is really hard to do, and checked the volume capability of your fuel system very carefully....

My guess: An exhaust valve will come apart, hit the piston, tearing it into a million pieces, allowing the rod to crater the block, and then you will have a few hundred pounds of pure junk sitting in your bilge...

I have seen that happen twice...

Then there is the drive, with 500+hp and a 9k lb boat...You already know to take it easy out of the hole...

The first time you have a few brews or try to pull up a skier with a hole shot, you will hear a 'Kaboom' with no traction after that.
===
Good luck!
Kent

vandeano

The boat , last year, did 46MPH with the stock 7.4MPI 26" cupped props (4600RPM)

Is it me, or does that not sound right? I would think you would be going a lot faster then 46mph. I would think more like 65mph. Im even surprised a stock 7.4 could turn a 26 pitch prop.
I can barley turn a 25' w/ my 502

Pat McPherson

Bravo IIIs have a different ratio...

Bob has been running with a supercharger for some time with good results.


Hey Bob,
Sounds like you put a nice package together...
Either rebuild your drive with XR components or buy a new B3 XR drive. There is a kit to convert your existing gimble to run the HP drive if you go with a new XR.
I would also ditch the stern jack, those things add lots of stress...

Fountaineer

My father just purchase a boat with a 496 and a Bravo III XR drive. Merc says the XR drive can handle up to 525 HP. You might be pushing it on a stock III with that HP

SCANDINAVIAN

Last season I hooked up a old (ap.-95) Bravo III (1:1,68) to my new single 496HO. Boat weigh ap. 4000 lb and ran 70 mph. @ 4900rpm. Had no problem at all!