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Need help choosing 454 mpi Cam!?!?!?!

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Need help choosing 454 mpi Cam!?!?!?!

Old 01-06-2020, 10:23 AM
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Default Need help choosing 454 mpi Cam!?!?!?!

Hello, Ive used OFO as a great resource for years now but this is my first time posting as Im starting a build on my 1998 Campion Chase 800 (27ft). I have the Merc 454 (7.4L MPI) 330hp I believe and am looking for input on upgrading the camshaft to gain a little more breathing room in the top end of the rpm range for longer trips. Everything in the motor is stock currently. Its getting pulled due to low pressure from the fuel pump, bad head gasket and a messed up injector. The guy who had the boat before me was very DIY and as a result the engine isnt as clean and put together as Id like it, so im pulling the entire setup to go over it and clean it up cosmetically and figured while it was out thats my best opportunity to add a little extra reliability in terms of quality of internals, as well as power.

Boat currently runs 62mph flat out light on fuel on the right water. Would like to do add more mid range to help with crusing as well as a little top end for those times we need to outrun the weather.

Any input is appreciated.
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Old 01-06-2020, 11:09 AM
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The best thing to do with that engine is leave it the way it came from Mercruiser. It is not a performance engine, and the costs to get anything out of it will far outweigh any performance gains.

If it runs well, pull it/clean it up and sell, then try to find a 454/502 Mag MPI, or perhaps a 496 Mag or Mag HO. You'll be well ahead of the game going that route.
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Old 01-06-2020, 11:51 AM
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Thanks Tom, the only reason Iíve considered going this route is because Iíve found it hard to come across a 454 mag or 502mag at a reasonable price here in eastern Canada and when I do theyíve got 600+ hours on them.

Iíve even laid out the plan to tear this motor down to the block, have it bored and put a 496 stroker kit in it, forged setup, switch the heads, and convert it to carb setup with a larger intake. Canadian pricing puts that venture around the 8K mark with all the labour being done by yours truly.

Which is is why I put it out there to see if anyone had had success just swapping out 2-3k worth of parts to kind of ďbring this motor to lifeĒ and just enjoy a trouble free setup that still makes decent power.
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Old 01-06-2020, 05:26 PM
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I agree with TomZ.

It takes at least 50hp to notice any significant difference and you may lose some valuable low end. Youíll be money and time ahead finding a complete 502mag and refreshing it.

Going the stroker route that you speak of youíll also need to upgrade the oil cooling system and fuel system, which for me was just shy of $2k in parts alone.
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Last edited by Baja Rooster; 01-06-2020 at 05:31 PM.
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Old 01-06-2020, 05:36 PM
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If you're going to spend the money on building up the short block with a bigger crank and so on, you're going to run into some serious sticker shock doing the top-end. The existing peanut port heads will not do the job. From a cost standpoint, it just doesn't work. Read through the site and you'll find this has been played out over and over again.

Start with a good foundation... sell what you have to recoup some of the cost.

A 454/502 MAG, if taken care of reasonably, will run a good 1000+ hours or more before needing major (as in bottom-end) repairs. You may need to refresh the heads at the 600 mark, but that' not a huge expense especially if staying stock-ish.

Hope this helps.
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Old 01-06-2020, 06:37 PM
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Originally Posted by Baja Rooster View Post
I agree with TomZ.

It takes at least 50hp to notice any significant difference and you may lose some valuable low end. Youíll be money and time ahead finding a complete 502mag and refreshing it.

Going the stroker route that you speak of youíll also need to upgrade the oil cooling system and fuel system, which for me was just shy of $2k in parts alone.
Don't forget the upgraded exhaust if you go bigger cam. It will (with stock exhaust) want to revert and throw all of your time and money into the scrap pile.
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Old 01-06-2020, 06:52 PM
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Here you go and $1,000 in extra parts to sell.
420hp 454 for sale
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Old 01-06-2020, 06:57 PM
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Default Cam

Tom Z said it perfectly
any change in cam will change the vacuum on that engine
that processor is set up to read a certain cam readings
these parameters are set in the characteristic maps internally and once you change the stock spec that motor will never right. Ever. Donít waste your money on that, build another engine with a nice big blower sticking out of the top. The chicks love blower motors
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Old 01-06-2020, 09:56 PM
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Originally Posted by activator40 View Post
Tom Z said it perfectly
any change in cam will change the vacuum on that engine
that processor is set up to read a certain cam readings
these parameters are set in the characteristic maps internally and once you change the stock spec that motor will never right. Ever. Donít waste your money on that, build another engine with a nice big blower sticking out of the top. The chicks love blower motors
Thanks everyone for the valuable input. so now that its clear this motor isn't the best choice for my goals......Ive tracked down a 454 MAG about 5.5hrs south of me, its a long block, completely rebuilt from the bottom up and he's suppose to have the recepits to prove it. Full forged internals, little cam upgrade, rectangle port heads and improved valve train. Its originally an EFI motor so my question is, does my 454 MPI intake setup work on a mag? I imagine the bolt pattern to be the same, but I was more concerned that the intake may be different and not flow enough to feed those heads or something? Can I have the computer re-mapped to feed the 454 mag? Do I even need to have that done?

GLENAMY 242SS - thats a nice setup for sure and a decent deal! but my exchange rate + shipping + taxes at the border drive that up to a almost 10K setup for me unfortunately

Thanks again for everyones input and feedback, this is my first boat, and well I know my way around an engine Im just not well versed enough at this point with the marine engine world
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Old 01-06-2020, 10:06 PM
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Does the engine package in question have an intake? Since it has been upgraded some, you might want to consider a carbureted set-up vs the EFI. The EFI set up will require a lot tuning that should be done on a dyno by someone that can write the tune properly. Having it be wrong leads to broken parts.
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