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502 mag mpi suggestion request on a budget

billy610

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I have a 1997 DCB 24 Extreme closed bow double step hull with a 502 mag mpi. I believe this motor was spec'd @430 hp by Mercruiser. The motor runs great, has about 300 hours and pushes the boat to low 70's on regular speedo.

I'd like to get 80-100hp more out of it keeping stock heads, crank, rods and fuel injection. I basically don't want a snowball effect and end up spending a bunch of money and having a motor that will brake the 1997 Bravo 1. The motor has the stock exhaust manifolds now, but I do have access to some GIL manifolds my dad had on his boat. Is it worth using the GIL's or should I budget for Imco manifolds? I don't mind going into the block to install better rod bolts and fresh rings. I can even have the block machined to a 509" for not too much as I've got connections on block machining(by someone that understands marine clearances) and CP Pistons is a good customer of mine, but is that needed for my goals? Can the stock heads make this extra HP with a little bench work? Can the stock MPI/ignition handle this with reprogramming? I'm hoping my goal is attainable without snowballing and spending $$ on aluminum heads, new injection or going to a carb/msd etc. then I have the Bravo in the back of my head all the time, which I already do since my past boats were V-drives.

I know there is local engine builders that have all these answers I can try to catch on the phone, but all they would get out of it is a possible exhaust manifold sale so I don't want to waste their valuable time.

I know there's very knowledgeable guys on here and would like some honest opinions.

Thanks for any insight!
 

Nates270

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my suggestion would be to look for the whipple supercharger kit that was made for these engines. bolt on and be done. occasionally these kits pop up for sale as i believe whipple does not produce them anymore.
 

Runs2rch

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Imco powerflows, cam, roller rockers, tune. 731 crane is what is in the 500efi. You will be right about 500hp.
 

Trash

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You will not get 80-100 hp by installing new rod bolts, Gil exhaust, fresh rings etc. If you are willing to get into the internals of the engine as stated, you might as well do it right. 80-100 hp will take a good heads and cam combo. Your existing EFI can handle all that with appropriately sized injectors and a tune.
 

Springfield

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Had a 97 280 Eagle XP with the 502, 64 mph bote, had about 350 hours on it. Put a procharger on it and know it would do 90...maybe more. Ran it for about 300+ hours before sold the bote with no engine problems (666 hours) but did rebuild the Bravo I at around 400 hours.
Now note I am a super senior and actually just cruised around 50 mph but had it if you wanted it. ;)

You know IF you are going for more HP more shit will give earlier. My .002 moment of share for you. :)

Oh ya, let me know the secret to owning a boat and thinking there is a budget.
 
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