I'm pushrods away from having it put together, then a stall and headers. 
big cube engine
I've heard that some 6.0 iron blocks can be bored to LS3 size (4.065" or 4.070"), but you need a good block with no core shift and should sonic test it before hand. Then use a 4.10" stroke crank (426/427 CID depending on bore size) or 4.125" (429 CID). But, strokes over 4.00" pull the piston too far out of the bore on the down stroke which wears the piston skirt faster and also the piston ring landings are thinner which sacrifice strength. Another down size is that a lot of clearancing is required for the longer stroke cranks.
It's better to stay with the tried and true 408 CID (4.030" bore and 4.00" stroke). But, you can get a rotating assembly that uses the 4.030" bore and a 4.10" stroke (418 CID) or 4.125" stroke (421 CID). Again, I personally would not go more than a 4.00" stroke on a 6.0 block. The LSX iron block is a different story though, they can handle bigger bores and longer strokes.
It's better to stay with the tried and true 408 CID (4.030" bore and 4.00" stroke). But, you can get a rotating assembly that uses the 4.030" bore and a 4.10" stroke (418 CID) or 4.125" stroke (421 CID). Again, I personally would not go more than a 4.00" stroke on a 6.0 block. The LSX iron block is a different story though, they can handle bigger bores and longer strokes.
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Thank you batboy. That's what I was wanting to know, I tried searching but nothing useful came up. If I was going with the lsx block I would go with a 454 but I can't afford the lsx block plus the machine work plus the internals...
If you go that big it would also have to be hard blocked and normally no boost or nitrous should be used. A tall fill is in order def!
Schwanke sells the 427 iron 6.0L shortblocks, but I believe they use a long *** stroke and a quick search on their site shows they no longer offer them, I am sure its for a really good reason also.
PS with a proper setup, a 408 can do some KILLER things. They can use a wider variety of head designs and make them work, like most of the larger runner cathedral heads, LS3 heads and some others.
Schwanke sells the 427 iron 6.0L shortblocks, but I believe they use a long *** stroke and a quick search on their site shows they no longer offer them, I am sure its for a really good reason also.
PS with a proper setup, a 408 can do some KILLER things. They can use a wider variety of head designs and make them work, like most of the larger runner cathedral heads, LS3 heads and some others.
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From: PA/MD
I run and love my 408....the real secret is you can run a cam in an engine this big that has a huge amount of duration, so big that you can throw the normal max scr factors out the window and still run on pump gas.....I'm running 12.5:1 static compression on 92/93 pump gas with full timing and 0 knock (a safe 8.22:1 dcr) 255/263 comp cam. I have my idle set at 850/900 and it pulls hard ad hell up to my 8,000 rpm fuel cut.
