Questions about re-power (7.4 to 502)
 

So I have posted a couple of times recently regarding my exhaust manifolds and possibly too much corrosion on my heads. I am trying to avoid a repower this year and will probably just slap a new set of manifolds on and run as long as possible..... BUT.

I am looking at new 502 long block for a decent price but I have a couple of questions... my current power is 7.4 MPI - GEN 6 - I would like a little more juice from a new powerplant and so far this seems to be the most practical and economical...

1) can I use all of the accessories (starter, alt, ps, fuel pump and cooler... ect.) from my old power plant.

2) Obviously my Bravo one should be sufficient as a drive... it is in excellent shape

3) Can I use the same intake and fuel injection set up

4) Will this be a pretty easy swap out... I see people are doing it all the time.


I am quite familiar with all components and operation of my 7.4 but dont know much about the 502. Also, I have done all of my own work on my boat but never swapped an engine out yet... what am I in for.

Thanks for your time....

Brian

going from a gen IV 454 to a 502 should be a direct bolt in, but I am not sure about the computer program for it to run correctly, somebody else will chime in on that, but I bet you will have to do something there...Rob

Thanks EZ.... yeah starting to learn a bit more.... meantime I am going to spend some hours on saving what I got.

You can just buy a GM crate engine, the 450hp 502 engine is the same as the Mercury 502 Magnum. Then just install your stock componets on it. Computer will have to be modified for the extra 100hp, possibly injectors as well, stock are pretty small on the 7.4.

If you buy an automotive crate engine, there are necessary steps that have to be taken to make it "marinized" You'll need to reset some clearances, brass freeze plugs, stainless exhausts, marine gaskets, etc.

Looks like I am finding complete engine packages ready to go... Will all of my wiring just plug right in. I am going to try to find the closest to a plug-n-play that I can. Outdrive is brand new and shouldn't be an issue... I am noticing all of the accessories on the 502's that I am looking at are identical.

Thanks for the help guys....

B

The external dimensions are identical. You might have some l;ittle things to deal with but it should be a very straightforward swap.

Two tips- one, take lots of digital pictures before you start. Two, put fasteners into ziploc bags and label them- or screw them back where they came. It might take a little longer but in reality it might save you hours trying to figure out what went where and why you have extra parts.

Brian,
FYI...I re-powered last year with a new 502 from Marine Power Service. The motor now has 100 hours on it and is rock solid. MPS was great to deal with. They actually had three base engines in stock. All of my 502 accessories bolted right on, all I had to change were the stock senders since they weren't compatible with my Livorsi gauges. Good luck...
Rocko C

Thanks Roco...

I will definitely check it out... The only difference I have is that my current power is stock 7.4 MPI. When I am ready I will call them to see what they have and that it should bolt right in....

Thanks again.

Have a good one.

B

as long as you order the 502 for the same generation (gen IV , gen V or gen VI ) everything should bolt on ,
and as for the program , i'd ebay for a stock ecm from a 502 , i saw one on there a couple weeks ago for 150 bucks , and will plug right into your harness where your ecm was , larger injectors are cheap too , another ebay thing in my opinion