I am in the middle of building a 489cid mark vi BBC and I was wondering if any of you know if there is a mark vi block that i can find that will bore to 4.5in. I beleave the 502 is close but It's a mark v and I've heard they are less desireable. I know the 572 is atleast a 4.5 bore and its a mark vi block but its a tall deck and I dont want that. My 489 uses a 4.25 stroke 1 pc crank and I have some eagle 6.385 h beamers. I plan to reuse these in the 540 if I can find a block that can handle it. Any advise would be great.

 

Dart doesn't even produce a one piece rear main seal, 4.500" bore, block. Only 4.250" bore is available.

 

yeah thats about what I've figured so far. Is the 572 a gmpp block or what. They say its a 1 pc rms so surely you can get it with the std deck height.

 

Most or all of the BBC 'performance' engines from GMPP are Gen VI engines. The crate 427 my boss bought about a year ago uses a Gen VI block (factory roller cam provisions and all).

The 502 is also a Gen VI and has a 4.500" bore, so thats probably the block you wanna buy to build a 540 with a Gen VI setup.

 

Anything with more than a 4-3/8" stroke requires a tall deck block but even trying to use a 4-3/8" stroke in a short deck is risky. To make anything with a longer stroke in a short deck is very risky as it puts the wrist pin too high in the piston to be useful or pulls the piston down too much which can contact the crank or camshaft.

The factory 572 uses a 4.560" bore with a 4.375" stroke in a tall deck block but there are other ways to make 572.

The GM 502 blocks are actually 4.466" (4.470") bore but they can be bored out to 4.500". I don't know how much more you can push them. The Dart 4.500" blocks can be bored out to 4.600" and will still have .250" thick cylinder walls. 4.600" bore with a 4.250" stroke makes a 565 which is a very common and popular size.