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mercruiser 502 mpi with bravo 3 drive, upgrade path and possibility

Old 08-09-2013, 09:04 AM
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Default mercruiser 502 mpi with bravo 3 drive, upgrade path and possibility

Hi, if the the last few details are as they should, Ill be the owner of a 30 fot boat, with 502 on brave 3 drive, it does 54mph at 4600rpm with 24p according to owner, (will verify), doing the test with owner tomorrow, but preparing so I have all the info right.

That motor has 415hp as I know it, its a 1996/1997 motor, with about 500 hours

I have mostly owned boats with twin outboards, or twin diesel, so experience is limited as big block inboards, but my 1000+hp 1969 camaro with bigblock and supercharger, has way less maintenance than the diesels... soooo after paying over $120.000 in maintenance on my previous boat over a short period Im going GAS and BIGBLOCK.


The riser/manifold allthough appearing to be in good condition, will of course need to be changed as it has many many years in saltwater, will the proper looking stainless headers , like 500 efi, 525efi etc actually yield any power increase? it allready has silent choice with large pipes out. so that part is ready, the silent choice system at times had to be helped a tad manuall he said to close fully sometimes, so probably needs new parts or unit replacement.

What can, or should be done to motor? and how much can the drive take? Ive blown up enough motors/drives/lower units etc over the years, and dont really want that, but I want it to be faster than 54mph, the hull definetly has potential. same boat does 48mph with 320HP diesel.

The 2 routes seem to be either a lower powerd like 3.5psi blower system, or new intake/headers/cams ? guessing if I reach 470-500 crank, the drive will hold, and I should be able to reach say 60+mph? compresssion on all cyls on motor are within a few % and seem solid, a valve overhaul was done in 2011.

It should be noted that we have a "weird" VAT / tax system, so anything allowing me to use the block I have, will not give me any new horsepower tax when tuning, but if I go to buy a new 525 or 632 or whatever, I have to pay lots of tax.

lastly, what happend to the forum? my old user account from 2005 was deleted, I used to hang here back in th days
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Old 08-09-2013, 04:56 PM
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Default mercruiser 502 mpi with bravo 3 drive, upgrade path and possibility

What you have is a pretty darn nice combination. But, if I were you I would seek the advice of a reputable marine engine builder before I did anything. The 502EFI/MPI is a great engine for your boat/drive combination. To add a blower probably eliminates using the Bravo 3. Before I would add anything extra to a 502 EFI/MPI with 500hrs I probably would re-ring, cylinder hone, all new bearings, check crank, check cam, new lifters, probably some better rocker arms, and all new gaskets. And, seriously check all the water passages for corrosion. That's a minimum. If I was choosing new exhaust for that combination I would choose Stainless Marine and not tube headers like the HP500/525EFI use. I would also have my Bravo 3 drive serviced very well. If I still had $2-3,000.00 to spend I would probably add hydraulic power steering to the helm and tune the props a little and maybe check for CPU upgrades for the motor. You would likely add a little power but would also have an ultra reliable combination. The Bravo 3 is great around the dock as compared to the standard Bravo.

Happy boating.

deboatmon
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Old 08-09-2013, 05:07 PM
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Thanks for replying quickly, your reply was very identical to a friend who runs a mercury/marcruiser shop, he said at that age, and hours, it would need new bore, hone, the drive would probably die at any time etc. so he wanted to put a whipple + proper stainless marine headers + new pistons + dyno +map. this would of course need, say a new 1XR.. but thats serious money, 8k whipple, 6k headers, 15k drive etc suddenly talking a nice bunch of cash there gone. then I can buy a 10 years newer boat, allready equipped with a 525..


a hone + new rings etc would of course be way cheaper,

is there any cam/lifter, maybe new heads? thats fairly cheap and could bump the power? 470-500hp would really be enough I think and then I could keep the 3'r drive. Maybe som E-top headers?

the head had some work done by a mercruiser shop, due to valve not closing fully last year, Im gonna call the shop tomorrow and ask around exactly what was done.

Tsts got a heat exchanger, so no saltwater, in the actual motor so it shouldnt have any issues on the block

The boat has hydraulic powersteering as standard from factory

I have never driven a bravo 3, only volvo penta duoprop on singlemotor boats, and I can tell I will definetly miss the agility of 2 sterndrives, and a thruster when all else fails.

the transom was replaced last year on it.

seller wants aprox 70k for the boat, but I think 55k or so would probably reflect more on what needs to be done.. also a trailer for it is around 12-13k usd here as 2nd hand trailers are impossible to get as US traileras are illegal here :/
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Old 08-09-2013, 05:08 PM
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