Sir Tripower

Hi folks,

can anyone of you explain the difference between Big Block and Small Block to me?

I always thought, that it depends on the displacement, but when I heard, that the new C6 Z06 with its 427 cui engine is called a Small Block, I know, that I'm not right.

So what makes a Big Block?

Thanks for your efforts

Gerrit from Germany

Simmo

different bore spacing
different deck height
different head design
externally much bigger

Sir Tripower

O.K. - but what are exactly the specs?

When is a Big Block a Big Block? What are the correct terms to say "That's a Big Block" or "That's a Small Block"?

Gerrit

SmokedTires

Externally the BB is much bigger. In the 1st pic you can see the BB has 7 bolts on the valve covers versus the SB only having 4.

MotorHead

The block of a big block is bigger, you can get the same displacement with a small block up to a limit ( 427,454 etc) but it's still a small block.

Sir Tripower

Does the definition only depends on the outer dimensions?

I have a '69 427/400 my own:



Isn`t there an "official" definition for "Big Block" engines?

Gerrit

silver84

cylinder center to center...
small block 4.4 inches
big block 4.84
{1 inch is 2.54 cm}
...
deck heigth,
sb 9.025
bb 9.8

CFI-EFI

You have a "big block". The definitions are many and mostly technical. The big block is a different foundation than the small block. Only the distributors are common between the two. Although the oil pumps will interchange. The big block is longer, wider, taller, and heavier than the small block. Typically, big blocks came in larger displacements than the small blocks. There was a 366 truck, big block, and of course the famous 396. The only small block produced larger than the 350 was the 400, from 1970 from 1980. The "new" 427, Gen IV, engine only shares the 4.40" bore centers with the original, 1955 Gen I, small block. Other than that it is a completely different engine.

RACE ON!!!

aobrien

Basically, what every one is trying to say is that there are two different engine block sizes. Big and Small.

The engine block is that big chunk of iron (or aluminum) that everything bolts to.

A big block has much larger cylinder diameters allowing for much larger displacement. Sometimes people will call a big block a RAT motor and a small block a MOUSE motor.

To complicate things... There have been several different generations of small blocks the first generation (GEN 1) was produces from 1955-1983 (not exactly positive about the years but it's close).

I don't know for sure, but I think that the 2006 corvette has a GEN 4 or GEN 5 small block. Each generation being subject to internal and external changes.

What I find interesting is that the GEN1 small block lasted for 28 years and from 1984 to 2006 (22 years) there have been 3 or 4 other generation engines.

Didn't they first produce the big block in 1965? I think that GM still makes big blocks, but the last one that got into a Vette was in the 70's.

skid

A small block can range in displacement from ~265-454 cubic inches (sometimes a little more with a tall deck block). A big block starts at 396 (except for big trucks) and goes to over 632 cubic inches.

Tom454

That's how I would have said it...

In laymens terms... the two blocks are generically different, sharing only a few parts. You cannot take a crank out of one and put it in the other. You cannot take the heads or intake off one and put it on the other. They are mutually exclusive designs... and each design has its own set of "version numbers" like software. Displacements overlap, so that is not the determining factor.

glen242

Just curious, a friend had a new '58 with a 348 tri power. Was that a big block or a small block? I do remember the valve covers being a a different shape than the standard 283.

Thanks,

CFI-EFI

That was the "W" engine, named for the shape of the valve covers. It came in 348 and the famous, 409 cubic inches. It is a different and short lived family, from about 1958 to 1963.

Back to the original question. Small block engines have narrow, 4 bolt valve covers, until the late '80s, when they went to the same shaped, "center bolt" style valve covers. All 8 valves in the head are in a straight line. Big blocks have wide, 7 bolt valve covers. The heads are of a "porcupine" design. The intake valves and the exhaust valves are at different angles.

RACE ON!!!

glen242

So the 348 was neither a small block nor big block? Just a bastard!

CFI-EFI

The mark IV big block and it's forerunner, the "Mystery" engine of the early, mid 60's MAY have had some of the "W" architecture built into them. I really don't know, for a fact. But the engines ARE quite different. "She's real fine...my 409!"

RACE ON!!!

Z-man

Simply stated, yes. For most of the '50s, '60s, and '70s, Chevy made two size blocks - Big and Small. There were many displacements available in each size. Big blocks were dropped since the 80s, or only used in trucks (lorries). The new 427s will be small blocks even though the old 427s were big blocks.

CFI-EFI

Maybe the best answer to the question, "What is the difference between the big block and small block Chevy engines?", is a question. What is the difference between Ford and Chevy engines? The answer? They are just different engines. The differences, far out number the similarities.

RACE ON!!!