GM 454 to 502 Upgrade (Gen 4)
 

Hi guys

I've got a broken Volvo Penta 454ci (7.4l) V8 Gen 4 engine.

Is it possible to upgrade to 502ci (8.2l) relatively easily?
Could the heads as well as bolt on parts be carried over considering the 502ci cylinder block is Gen 4 too?
Could the crankshaft and camshaft also be carried over so I potentially 'only' need the bare block with pistons?

Many thanks
Martin

yes ,if its a gen 4 , you can swap it all over except the pistons .

Hi

Ok cool. Many thanks for the clarification.

Do you have an idea where to get a good 8.2l Gen 4 block from?
In Europe it seems to be a quite difficult job.

Cheers
Martin

I may be wrong...But I don't believe there is a mark IV 502 block. It wasn't made by chevy until the early 90s, so 502s are Gen V or Gen VI. Both Gen V and Gen VI do not have a boss for a fuel pump. If it is a Gen V, your heads, crank, oil pan, all will not swap over. If it is a GenVI, your heads will, but crank, oil pan, timing cover cam shaft, (I am sure I am missing something) will not. If you can find a Gen VI shortblock with a cam installed already, you can use your heads, and would only need to get a new oil pan, timing cover, and figure out your valvetrain since Gen VI is a roller cam. All accessories should bolt up

1990-1992 mercury had a gen4 502. not very common

https://www.mercruiserparts.com/502-...8-1990-1992-0c

Mercruiser used the gm “bow tie” block for a mk iv 502. Easiest to use a dart or Merlin block now.

Ah ok.

So doesn't sound likely to convert the broken 454ci into a 502ci easily.
I might stick to the 454ci gen 4 configuration then if swapping parts between generations isn't as easy as I thought.
Finding a good condition Mercury 502 gen 4 bare block or short engine doesn't sound likely as well.

Does anybody have a good address for 454 gen 4 bare blocks or short engines?

Cheers
Martin

What broke ?

Engine froze so apparently engine block or heads broken.
It still runs fine but you can see oil/water emulsion coming out of the air filter or crank case breather hose.
Only seen a video so far. Gonna pick the boat up in 1 week.

As it still runs fine (the guy I bought it from sent me a video, didn't ask him to crank it myself) I'm not really convinced that the block is cracked.
Not sure if these engines tend to crack the head or the block when they freeze. Freeze plugs came out and were replaced, then the current issue appeared.
That's how I bought it.

I'm new to boats and GM V8 engines so trying to identify the best/most cost efficient repair option with all my questions.

Cheers
Martin

Put a request in the wanted section for a Gen 4 or 5 502

I think the cam tunnel usually cracks, if that's it, the block is scrap. You would probably be better off buying a complete motor and just switch the bolt ons. Maybe something like this with brass freeze plugs and stainless head gaskets. https://www.summitracing.com/search/...-size/8-2l-502

I've seen a Ford 351W push out freeze plugs and survives. I've never seen a BBC push out freeze plugs and survive. Usually they crack in the lifter/cam area without pushing out the freeze plugs. I'm sorry, but it's junk.

There is no Gen 4. It's a MkIV. But we knew what you were talking about.

There are no problems with installing MkIV heads on a Gen6 block. You just have to run Gen6 head gaskets. If you put MkIV heads on a Gen5 block, there are some issues that you need to address.

MkIV blocks will freeze crack in the lifter Valley. Can't be reliably repaired - the block is trash.

You can swap in pretty much any 502 long block. If you do a short block and reuse your heads, you should choose a MkIV or Gen 6.

If you go with a 502 block, you cannot reuse your 454 crank without rebalancing. Stick with a 502 rotating assembly.

Your Volvo 7.4 uses a regular no-frills 454 longblock. Cast crank, small rod bolts, mild cam, oval port heads. None of these are parts you should worry about jumping thru hoops to reuse.

There are things you need to do to a passenger car big block to run it in saltwater.

Sorry for mixing Mark and Gen up. I'm new to the US engine world so learning quite a lot at the moment.
Once I have the boat I will strip the engine and have a look at what actually cracked.
If it is the block which means I can reuse the heads I probably then get a 502ci big block short engine (block, crankshaft, pistons, conrods). A shop is offering a refurbished marine short engine for $2400 in Germany to then carry over heads.
I reckon new flywheel is required as well but not the biggest deal I suppose.

I keep you guys posted and might require further help once I stripped the engine.

Many thanks guys for your help so far!
Looking forward to get get the engine running again.

Martin