I was reading a Chevy engine spec 572CI 10.2 and it has the same stroke as by Merc 540CI 4.375" the Merc bore is 4.440 and the Chevy was 4.562 or so. If I bored my 540CI to the same bore are they now 572CI? Will I only need new rings or is this a piston swap on a bore this size?
Thanks

Bore .120, new pistons, rings, balance the rotating assembly

using a 4.440 bore and a 4.375 crank will only give you 541 cid..

you probably have a 4.250 crankshaft,if you change your rotating assembly in your 4.562 bore engine to a 4.375 chank rods and pistons you will have a 572 cid..going to a 4.500 stroke will yeild a 588 cid...

here's the formula to determine how far you want to go


bore x bore x stroke x .7854 x 8 =

I'm thinking he's not really getting the bore, stroke, rod length, and piston clearance thing. To simply answer his question. If you bore the block out to the same size, yes you will need to change the pistons and rings. No it won't give you a 572cu.in. unless you change the stroke which would mean changing the crankshaft. It gets complicated till you get it.

I am guessing that he has a merc bulldog, which is a 4.44bore and a 4.375 stroke. I know most are accustomed to a 540 on a 4.25 stroke, but that is not how mercury went about it, I actually think it was 542ci. So yes if you bore to 4.562 you will be at a 572. Be careful as that is getting pretty close on a GM block. Some can go to 4.6 bore, but it would have to be sonic wall tested to be sure, so if you end up needing another bore after the 4.562 you might be out of luck, it just depends on the block.

Yes they are 540CI Bulldogs so the 4.375 is correct.
Thanks

I would not bore it out more than .060 over. I think the bulldog was a 454 tall deck or bowtie block. The 572 is a 502 style tall deck block similar to the aftermarket blocks. Completely different than what you have. The Bulldog is a great motor but it uses a mild flat tappet cam. Call RMbuilder and get a custom roller setup that will get you some big HP numbers and still be able to idle.