Looking to instal a 496 Mag HO where there was a 7.4 MPI
 

Hey guys...

I have a 2000 Checkmate 259 Convincer that originally came with a stock Mercruiser 7.4 MPI (Gen VI) and now that it is time to repower I am looking at a 496 Mag HO. I was wondering if anyone has done this swap and what I may be in for. One thing I notice is that the engine I am looking at came off a boat that has a full hydraulic steering set up where mine is just a cable... the power steering pump is definitely different but I am not sure if this will be a problem. I also am wondering if I will have any issues with the main electrical harness hookup. From what I am reading its either 10 pin or 14 pin right? What if mine is not the same as the new engine. Owner of the motor I am going to purchase says he will also include the smart craft gauge he has installed in his dash... I would love to install in mine... is this going to be a nightmare? Any insight greatly appreciated.


Thank you,

Brian

Why not just re power the 454 to give a little extra punch? Might actually be cheaper than buying a new engine?

Merc still uses the 10 pin connector without change. There are other cables which connect other sensors to the ECM. There is also the CAN bus which goes to the smart craft gauges and sensors

This engine is sssso done... 1200 hours in SALT!!! It owes me nothing! I have done manifolds at least twice, heads once, intake manifold once and now one cylinder is gone. From what I understand the 496 HO is a great motor... very reliable with a great mid range cruising speed for a boat like mine.

So then I take it I should be able to run that smart craft gauge with a separate cable? I imagine all of my analog gauges will still work? And do you have any idea what I am in for with that power steering pump?

Thanks for the reply.

Just replaced mine with the same setup with no alterations and love it, easy conversion

the 454 block may be salvagable. they are pretty tough. the heads are good for mooring bouy anchors for small boats. whatcha doing with the MPI setup? needless to say, you will part with nothing till the boat is running with the new power.

Go with a 454 or 502. The 496 is a white elephant. It will go in but you will probably need to relocate the exhaust tips.

If the donor boat has analog gauges then your gauges will work as-is. If the donor boat has smart craft (SC) gauges then you will need to change out the gauges. If the SC gauge you have is the speed/tach then just need the junction box and cables. Here is a link to SC install manual
https://mercurymarine-gsdesign1.netd...stallation.pdf

As for the hydraulic steering on the donor boat, it will not work on yours unless you change to hydraulic steering.

There is definitely some good stuff left on my motor... in fact most of the MPI stuff is new as I had to replace fuel rail less than 30 hours before catastrophic failure. Also, the upper plenum in good shape but lower manifold shot. Heads are probably toast as you say as well. Brand new seawater pump and a few other things that I could probably hold get something for as well. If you are interested in any of this let me know. Its all coming out soon.

Thanks