I know the stock cranks are interchangable but I was asking about the 4" crank. is it interchangable without needing a new/deeper oil pan??

 

Nope, the stock pan will fit fine. Same crank and oil pan all the guys with 408 are running. They just use the 6L block.

 

Its when you go up to a 4.1" crank that you start running into issues with the stock block.

 

I have looked into doing the 3.893-3.903 bore and have always questoned what kind of cylinder wall thickness is left after a .123" bore? If you have a answer to that question, then I could beter judge if boring out the engine that much would be reliable and worth it. I would like to run some boost with this engine if I do decide to build it, and I don't want to worry about cracking the block.

 

your cylinder walls will be just fine after the punch.
gm designed the 4.8 / 5.3 blocks to be machined out to LS1 specs
and still be cooled by the stock radiator.

 

What does cooling have to do with me wanting to know how much cylinder wall thickness is left over after a .123" bore? I know people have done the 5.7 conversion on these blocks, and I know they run. The thing that concerns me is if someone was to run 20+ pounds of boost on one after boring it out to accept a 3.903" piston, are the cylinder walls going to have enough strength to handle that kind of horsepower? Assumptions can be very costly and I would rather be safe with less bore then be sorry.

 

well i work in a plant and not in a machine shop.
so i have no idea of how thick the cylinder walls are in your block,
but for a few bucks i am sure a machine shop close to you can check
your block and give you a straight answer.
good luck on finding your 40 over pistons, as far as i know, they don't make them.
so your only chouses are to make a very expensive custom order,
or pick up a set of stock pistons at 3.893 or over sized of 3.905 that
your block can be safely bored out too.

 

Blown Chevy on here has an iron block 5.7 and has run I believe up to 15 lbs on it without any problems. I have never heard any of the guys who have punch out 5.3 to 5.7 that have had any problems with cracking cylinder walls, even with moderate to high boost. I believe it is a non issues.

20+ lbs of boost is a whole other issue on these motors. They are not old school SB's. They flow MUCH better and the 20lbs is a **** ton, even for a built motor. I think at that level, you will have more problems keeping the heads down then clacking the cylinder walls. I'd say 15-18 is about all you would want to run for any kind of longevity.

 

Mahle makes forged pistons in .010, .020, .030, .040" over stock 4.8/5.3L bore (3.780"). I guess I can take my block to a machine shop and see if they can sonic check it and see what kind of material would be left over in all the cylinders if I do decide to go with a 3.903" bore.

 

well said!