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