OK here's a question that I've NEVER got a good decent answer for.. How is an engine determined to be a bigblock or a smallblock?

I know it is NOT just size (cubic inch) of the engine,, there are some sizes like the old 400's that could be had either way.

Noone makes bigblocks anymore, so it's probably gonna need an old fart to answer the question

 

It's generally the height of the deck on the block and the stroke of the cylinder. Small blocks are usually under 3.5 inch stroke length whereas a big block is longer.