Okay, here's one that I can't even get some mechanics to answer: What is the difference between a small block and a large block engine? Hopefully this is NOT a stupid question, but I've been attempting to find an answer for quite some time.....
Nitro

 

Size? :P (not just a smartass re-mark)

 

Bore spacing. A SBC has the centers of the cylinders closer together than a BBC. There's also a bigger BBC which has a 5" bore space for those really big 700+ CID engines.

Some engines such as Oldsmobile have the same bore spacing so a 350 Olds block is roughly the same as a 455 block so there is no small/big Olds blocks.. The difference is in the stroke and the overbore.

You can have a 400 SBC and a 396 BBC so it's not just about size. Chrysler made a 400 SB and a 383 BB.

There's also a lot more technical differences between a SBC and a BBC but the classification is based on the bore spacing.

 

Chrysler NEVER made a 400 SB. Their 400 was a big block. You are correct about the 383 BB though. And there most certainly was a small and big block Olds. The big blocks had a taller deck height. Try bolting a 350 Olds intake on a 455 or vice versa.

 

Pontiac V-8s were all the same physical size. Displacement being determined by bore/ stroke combo.

Tim sends

Edit: not sure about the 301 motor, though.

 

Ahh but a tall deck does not make it a big block. I believe you can interchange heads on the different models making the bore spacing the same. The normal BBC engines have 2 deck heights 9.8 and 10.2". Ford produced many different types of engines all roughly in the same CID range and parts do not interchange. I never did understand the differences between Clevland, Windsor or Modified blocks.

Pontiacs is another good example. Caddy engines are 425 and 500 CID and that was just the stroke.

 

But you made an incorrect statement about Olds engines. You had said that just because Olds engines share the same bore spacing, they are identical. And had also made the comment that a 350 olds and a 455 olds was basically the same block. Chrysler also made a low-deck and a tall-deck big block. The 361, 383 and 400 are the more common low deck big blocks, while the 413, 426 "wedge" and 440 were the tall deck big blocks.

 

Hmmmm, the differences....


How about the block and everything that bolts to it...

 

I really don't get much into the intricacies of the engine. ALl I got to say is look at the 455 block, and 350 block. Which one looks bigger?? The 455. There you go big block.
Simple.

 

difference is bore spacing

SBC, bore spacing, center to center, is 4.4 inch
BBC is 4.84 inch.

commonest deck heigth is,
SBC, 9.025,
BBC, 9.8, I think.

both had other deck heigths

 

Put another way...

 

There is no such thing as an Olds "big block" or "small block".

Bore spacing is the defining characteristic for "big" and "small" block, not deck height.

Just like there's "standard deck" big block Chevy motors, and "tall deck" big block Chevy motors. They're not "big block" and "even bigger block" or something. Or, in the F*rd product line, look at the Windsor blocks; a 302 isn't a "Windsor small block", and a 351 a "Windsor big block". Those 2 motors are EXACTLY the same difference between them as Olds motors. Olds blocks are all kind of big compared to some others, but some are tall deck and some are short deck. NOT "big block" and "small block".

Apart from just the bore spacing, the SBC and BBC have other design differences. The BBC has all 4 cylinders turned the same way on the head, so the 4 exhaust ports are evenly spaced. The SBC has both the intake and exhaust valves at the same angle, where the BBC is a "porcupine" or "semi-hemi" arrangement, with the intakes tilted toward the intake side and the exhausts tilted the other way. That's what makes them breathe better in general. However it also makes their combustion chambers HUGE, which in turn forces them to require domed pistons in order to get their compression up into the "performance" range, which makes them less efficient and have more emissions.

Alot of little stuff interchanges; oil pumps, lifters, distributors, starters, engine mounts, flywheels (subject to balance differences, if any). Not too much else does though. Heads, cams, cranks, intakes, etc. are different between them.