What is the difference between a small-block and big-block engine?

They are two designs for engine blocks. One is smaller than the other. Back in the day, technology permitted the size of a small block to about 350 cubic inches. Now, they can bore out the block further by making a stronger block, and using more exotic metals like titanium. The difference between a small bock and a big one is the distance between the dead center of each bore. Chances are, a 427 vette with a small block will be lighter, have more horsepower, but have a narrower power band with a little less torque. It will also be capable of significantly higher rpms because of the stronger metals; and the fact that they get the larger displacement from added stroke, instead of bore. The old school big block will have a wider powerband, but will be a lot bigger. Assuming both cars have the same overall specs (including weight, which will almost never be the case), the big block will win off of the line, but the small block will gain that back at higher speeds.

The current Generation 3 engines are a completely different design than the old small blocks and big blocks. The LS7 at 427 cubic inches is the same design as the LS1, at 346 cubic inches. The LS7 just has a larger bore and longer stroke. Displacement has nothing to do with the term of small block or big block, those terms both refer to the engine design, or platform. Displacement is a measure in cubic inches, or centimeters of the swept area of the cylinders. It is possible to build a small block to over 500 cubic inches, or a big block as small as 300 cubic inches by varying the bore and stroke.

Dimensions, basically. The measurement of the blocks' overall length are different, as well as the bore center-to-center measurements. A big block is also taller, when measured from the oil pan mounting surface to the intake or cylinder head mounting surfaces.

ONE ...BLOCK...IS ...SMALL... AND... ONE...BLOCK ...IS ...BIG DID YOU GET IT THAT TIME????

the small block's block is smaller than the big block's. just a bigger and faster engine

In GM engines it really is the actual cylinder block size. The limiting factor in a traditional small block chevy is the stroke length due to the size of the block. You can only fit so much crank in that small of space. The big block on the other hand is much larger in physical size and can accept longer strokes and bigger bores. The limitations of a traditional small block generally 4" bore x 4" stroke making roughly 400 cubic inches. Where as a traditional big block can reach up to 510 cubic inches without added machine work. What you have in the Z06 is a "small" block but it is not the traditional "small block" casting. Meaning you cannot pick it out of the vette and bolt it in place of a small block in another GM vehicle. And traditional small block parts will not bolt on your engine.

Personally I have never seen one, and to my knowledge, any CID past 350 is considered to be a big block. Now I do know that there is a difference between a normal/wide block (Same CID but different manufactures). Not sure who told you a 427 was a small block, well lets just say I believe they are incorrect.