First of all what is it that defines the difference between a big block and a small block. I ask because now i believe motown has a small block that can be bored all the way to 454. How can you have a bbc 454 and an sbc 454. I know the answer is because the bbc starts out bigger where as the sbc needs to be bored but what is the cut and dry difference that seperates the too (wow do i ever ramble)

second of all what qualifies a transmission gear as an overdrive gear? What makes it different from the rest of the gears. Im not sure if its a different answer between autos and manuals but if it is give me both.

 

well,a big block is actually a "big" block. if u look at them side by side ull see that the big block is by far alot bigger than a small block.

and ur question about overdrive is some gear ratios (manual and auto alike) are like 1.55 of 2.35 or so. an overdrive ratio is like a .7 or .6. In overdrive the transmission output shaft (what the driveshaft is connected to) is spinning faster than the crankshaft thus giving u better gas mileage at higher speeds.

hope this helps

 

i know a big block is physically larger but is there like an outside size of the block in numerical form that defines the difference between the two?

 

BBC = bigger bore + bigger strock. Strock being the key word.

T.