What makes an engine a 'big block'?

[Mr Twisty]

Originally Posted by topgun1

I love the 454 engine. If I ever get a 69 chevelle SS, I want that engine in it!

thanks for all the info to all, but still....what are the actual specifications that make a block a "big block"? is it a very blurry line or a fine line--i.e. certain bore and stroke, certain displacement, liter, etc.

DGthe3 gave good technical info on 'why'.... If you understand deck height and bore spacing you'll understand.

[Mr Twisty]

Bore diameter and crank stroke determine cubic inches (and cubic litres).

Simplified, do this... take 4 pennies and line them side by side in a row. Then do the same with quarters. That can represent your difference in bore size and spacing.

[DGthe3]

Originally Posted by MisterCamaro69

DGthe3 gave good technical info on 'why'.... If you understand deck height and bore spacing you'll understand.

Suppose I should explain those things then ...

Bore spacing is the distance between the centerlines of the cylinders. This isn't to be confused with cylinder bore, which is the diameter of the cylinder. It is the main factor in how big of a bore your engine can safely have.

Deck height is the distance from the centerline of the crank to the top of the deck (where the heads meet the block). This determines the amount of stroke an engine can have (distance the pistons travel).

Together, bore and stroke determine total engine displacement.

[Mr Twisty]

Originally Posted by DGthe3

Suppose I should explain those things then ...

Bore spacing is the distance between the centerlines of the cylinders. This isn't to be confused with cylinder bore, which is the diameter of the cylinder. It is the main factor in how big of a bore your engine can safely have.

Deck height is the distance from the centerline of the crank to the top of the deck (where the heads meet the block). This determines the amount of stroke an engine can have (distance the pistons travel).

Together, bore and stroke determine total engine displacement.

I figured the coin deal would help simplify bore spacing since larger diameter needs larger spacing.... in this example anyways.

The only 'stroke' metaphor I came up with was X rated.

You COULD give the history of the chevy small block, and THEN go on to the mystery motor and development of the big block.... in detail

... oh yeah... and maximum bore and stroke, along with their displacements, for each block.... or recommend a good book instead of write one.

[Jicata]

Cubic Inches.
Both my cars are small blocks.
Camaro = 376
Mustang = 305

[topgun1]

Originally Posted by MisterCamaro69

I figured the coin deal would help simplify bore spacing since larger diameter needs larger spacing.... in this example anyways.

The only 'stroke' metaphor I came up with was X rated.

You COULD give the history of the chevy small block, and THEN go on to the mystery motor and development of the big block.... in detail

... oh yeah... and maximum bore and stroke, along with their displacements, for each block.... or recommend a good book instead of write one.

much appreciation on the explanation. At least I'm glad I already knew the difference between bore spacing and bore diameter though to begin with but deck height was a new term to me, although I know stroke.

[DGthe3]

Originally Posted by Jicata

Cubic Inches.
Both my cars are small blocks.
Camaro = 376
Mustang = 305

Has nothing to do with displacement. There are 7L small blocks (427 cu) and there were 348 cu big blocks (5.7L).

[Mr Twisty]

Originally Posted by topgun1

much appreciation on the explanation. At least I'm glad I already knew the difference between bore spacing and bore diameter though to begin with but deck height was a new term to me, although I know stroke.

Here's a nice short writeup about the big block from Super Chevy magazine...

Mark IV Big Block Chevy Engine - The Mark of Chevy Power
Where Chevy Muscle Really Lives
From the July, 2006 issue of Super Chevy
By Paul Zazarine
Photography by Courtesy of GM
Chevy Mark Iv Big Block Motor 1965 Corvette L78
"Porky" Pine rides atop the Mark IV '65 Corvette L78.

The legend began on the high banks of Daytona in February 1963. A handful of Chevrolets arrived for the Daytona 500 with something "mysterious" under the hood. While Ford and Chrysler expected to compete against Chevrolet's venerable "W" head 409, the Bow-Tie guys had a rather large surprise waiting for them. As Junior Johnson's Chevy thundered around the track at speeds in excess of 160 mph, every soul from the garages, to the pits, to the stands knew that was no W block. Hot on Junior's heels was Johnny Rutherford in another Chevy. The Chevrolets of Ray Fox, Smokey Yunick, and Bubber Farr all ran with power unmatched by the 409, and Ford and Chrysler cried foul. What was this "mystery motor" that Chevrolet was running?

Inside Chevrolet Engineering, it was called the Mark II, a 427ci V-8 that had no bloodline with the 409, which was dubbed the "Mark I." The word "Mark" was derived from the European tradition of using "Mark" to designate succeeding phases of a design. Instead, it was a totally new design that started in the summer of 1962 when Chevrolet Engineering's Dick Keinath started work on a replacement for the W block. Keinath started with the same bore centers (4.84-inch) as the W block. To keep things differentiated in the minds of Chevy engineers working on both engines, the planned successor to the W block was dubbed "Mark II." It was this big-bore, short-stroke 427 powerhouse that tore up the Daytona high banks.

The Mark III was a 1963 design study that had features like the Mark II, but had a bigger bore center. None were produced, since it required too much tooling money at the Tonawanda engine plant to change bore centers. The Mark IV went into production in 1965, displacing 396 ci. Mark IVs were subsequently produced in versions of 427 and 454 cid. Deck heights were 9.80 inches

The cylinder heads were kept under wraps at Daytona in 1963, and all throughout the development process. Less than 50 of these engines had been cast before GM slipped out of racing in January 1963. The large-diameter valves were canted, causing them to stick out at odd angles, which then lead to the engine being nicknamed "Porcupine."

From 1965 until it was discontinued in 1974, the Mark IV big-block was produced in a variety of horsepower configurations. It served duty in everything from mundane station wagons with trailer packages, to pavement-melting super Chevys that ruled the streets and the drags.

Even after they were discontinued from production, the Chevy big-block continued on as the GEN II crate motor that powers drag cars, street rods, and the hottest street machines today. Like all great engines, the Chevy big-block will be around to power street machines for generations to come.
Chevy Mark Iv Big Block Motor 1965 396 Side View

The Mark IV 396ci V-8 was introduced in 1965, and was available in the Corvette and the full-sized Chevrolet. With the valve cover removed, the staggered arrangement of the valves is clearly visible. Header-like exhaust manifolds were extremely efficient.

[Apex Paul]

Originally Posted by DGthe3

Bore spacing is the distance between the centerlines of the cylinders. This isn't to be confused with cylinder bore, which is the diameter of the cylinder. It is the main factor in how big of a bore your engine can safely have.

My understanding is that Bore separation (spacing) is the defining character for a big block. I should have been as clear as you were when I posted earlier.

Now THIS is a big block...

[big hammer]

Originally Posted by AZCamaroFan

simply put it's the size of the engine block. A 409 and a 283 were completely different engines, with different size blocks. Same for the 327 and 427. The 454 was the last of the 'big blocks' at Chevrolet. The 427 in the current ZO6 Corvette is actually a 'small block'.

actually the 8.1L in the early-mid 2000's was the last production line big block.

[helmincamaro]

Originally Posted by Apex Paul

My understanding is that Bore separation (spacing) is the defining character for a big block. I should have been as clear as you were when I posted earlier.

Now THIS is a big block...

idk about you... but this is what I call a big block:




710 cubic inches per cylinder (20 cylinders).... so roughly a 14,200 cubic inch engine, oh and they come with single or twin turbos and push 6,000hp at around 950rpms. Just as a reference, I'm 6'-2" and if I'm standing with my feet level with the bottom of the oil pan.... I'd need a step stool to look eye level at the valve covers. Don't think about trying to fit it under your hood, it weighs over 16 tons.

[spyderbuddy]

No man that is not a big block Thats a monster motor

[AZCamaroFan]

Originally Posted by topgun1

I love the 454 engine. If I ever get a 69 chevelle SS, I want that engine in it!

thanks for all the info to all, but still....what are the actual specifications that make a block a "big block"? is it a very blurry line or a fine line--i.e. certain bore and stroke, certain displacement, liter, etc.

I'm not sure there are specifications. I think at the time the term came into use there were smaller blocks and bigger ones. Now they're all about the same size.

[DGthe3]

Originally Posted by AZCamaroFan

I'm not sure there are specifications. I think at the time the term came into use there were smaller blocks and bigger ones. Now they're all about the same size.

They are, but its not because there is some new 'medium block' being used. There are no longer any big blocks being built by GM, and I assume Ford and Chrysler have stopped as well. They still make big block crate engines, but nothing comes from the factory with them anymore. Everything is based off small block architecture.