Theoretical small block chevrolet.

Can and SBC with 4.125'' bore 3.00'' stroke (321 ci) be built out of stock parts? has it been done before?

 

I've pieced it all out for a 4.125 X 3.25 (327 stroke) which is 347" IIRC. If you use Nissan FJ24 rods and grind the crank down to fit the big ends. You will need spacers to fit the 302 crank in the 400 block...which isn't the most stable at high rpm...which leads me to:

One word of caution...you will have to rev the thing like an air sander to get anything out of it, which means a TON of money upstairs in the cylinder heads...

 

I Knew about the rpm issue, I just wanted to know if the formula I meantioned is doable.

 

Yeah, it's been done. As mentioned you will need bearing spacers to use a factory crank. If the spacers are done correctly they aren't really an issue...but whether this combination is a practical one is debatable.