78D200

I had a co-worker come up to me this morning and ask "What makes a SB a SB and a BB a BB?". I told him its the physical size of the block itself. He then asked "What is the measurement that defines whether a motor is a SB or a BB then?" I couldn't answer him.

Does anyone know exactly or even roughly what the physical defining dimensions are that classify a motor as a SB or BB? If someone has a SB and a BB Mopar sitting in their shop, can you take a measurement of the block (height, width, length) and post them up with the CI of the motor. If it is bored and/or stroked, please post up original CI.

slade

im not sure myself chrysler had bb with small cubic inches back in the day. this may be a question fotr the google button

440roadrunner

There is no "official" BB / SB definition. None of the manufacturers refer to any of their engine lines as small or big block. It's strictly automotive slang.

In wedge designs, the older "polyshere" related stuff was called an "A" and when the 273 came along, the changes then changed to "LA."

The original "big" block (350 or whatever it was, then 361, 383) was called a "B" engine, and the "R"aised deck 413 an RB

So Ma was "A" later LA, and "B" and then "RB" so "B" does not stand for "big."

Also, it irritates me when people call a "poly" a "wide block." The "block" in a poly is very similar to an LA, in fact, it's the predecessor!!!. If you were to strip an "A" and "LA" block down bare, side by side, you'd have to know some details to tell the difference.

bremereric

A RB is about a 1.0" higher and 1.5" wider.

BuckNeccid

I've always thought it was a comparison between the engines offered by that manufacturer. Most have either a small v8 and a large v-8 and it's just easier to refer to them in big or small.

Seanzie1405

I always thought it had to do with the width and height of the deck but I could be wrong

Dave E

You know that is an incredibly good question... I have never really pondered it before now but that really intrigues me. There was a time that Chrysler produced the 318 "wide block" so is that considered a "big block"? For me personally I have always considered the 360/383 the defining small block/big block line. Just my personal thoughts.

Coronet 500

Interesting conversation, my Dad always had Big cars Big engines, 383, 440, GM 455. Always bought them used from his good friend who dealt in cars. When he bought his '79 Lincoln Town Car 400ci, he thought he was getting another Big Block, when I told him it was the newer M engine based on the Smallblock, he was sooooo Pissed he almost sent it back.

78D200

I've always thought it was based on CI but that wouldn't hold true with the bore/stroker kits out there now for SB motors.

Still wondering if anyone has/have some SB and BB kicking around where they can take some overall measurements.

440roadrunner

I try to discourage people from calling "A" engines (poly) "wide blocks." The only thing that makes them look big is the HEADS. The FACT is that if you strip down a 318 LA and an "A" the blocks would be difficult to tell apart unless you know what to look for!!! The LA engine IS IN FACT based on a poly block and in fact some of the early hemi's are based on the A block. In fact the new 3rd generation hemis are based on a small block!!!!

This would be the same idea as thinking a 426 hemi s a "bigger block" than a RB wedge. A hemi block and an RB block are VERY similar and in fact the hemi block is BASED on a wedge block. The heads are what makes a hemi "so big."

Dave E

Right... the hemispherical head with the valves in the center are what makes the Hemi look so big... I have always heard the old term "wide block" never really stopped to look into it.