What is a "big-block", and why is it different from car to car?

What is a "big-block", and why is it different from car to car?

If you've been around MCM for a hot minute you'll remember Marty "big-block swapping" 2SEXY, and now doing the same thing for their quest to BUILD THE WORLD'S FARTEST MIDGET (CLICK EP1 HERE, and CLICK HERE for EP2). 

Our mate David Freiburger loves his big-blocks and explains why they're awesome.

"Big-blocks carry a swagger that you just don’t get with any other engine," he says. "Besides, cubes always adds the potential for more power, even boosted. And a 500hp big-block will be more tame and have more torque than a 500hp small-block (assuming the big-block is of greater displacement."

So what makes an engine a "big-block" compared to a "small block" or any other kind of block?

While some people believe a big-block has to have more than 400 cubic-inches (6.6-litres) of capacity, but this isn't the case as there have been big-blocks as small as 348ci (5.7-litres). It actually depends on which manufacturer you're talking about, as it can come down to bore spacing and deck height, and the external size of the engine.

What is deck height? That is a measurement from the centre-line of the crankshaft to the top of the cylinder (where the hEaD gAsKeT goes). Small blocks are shorter, big-blocks are taller. Simples, right? 

The other marker used to identify some engines as big-blocks or small-blocks is the bore spacing. This is the distance between each cylinder bore. Complicated, I know, but the wider the spacing will generally indicate a larger capacity, with a bigger bore meaning more cylinder volume, and hence larger capacity. 

Now, you may think Ford's new 7.3-litre "Godzilla" pick-up truck motor might be a big-block as it certainly has the capacity for it, as does the LSX454 and LS7 V8s from GM. However, these engines' bore-spacing and deck height measurements mean they're categorised as small-block engines! 

Pick-up trucks are actually the reason these engines exist. Chevrolet were the first manufacturer to bring out a "big-block" way back in 1958, primarily for use in their trucks with much larger capacities than what was offered in their passenger cars.

Simple, low-revving, torque-rich and designed for reliability the extra capacity over Chevy's new small-block V8 (introduced in 1955) meant fitting these big engines into passenger cars was a cheaper, easier way to make the cars faster. And they were far cheaper to produce than the then-top-spec Rochester fuel-injected 283ci small-block. 

These first big-blocks started off at 348ci but soon grew to 409ci (as used in the '63 Impalas, pictured above) in the early 1960s, as the quest for power and race wins took hold. Chrysler and Ford also brought out their own large-displacement engines, as did Pontiac. However, this is where the big-block story gets sticky.

While Pontiac released a range of giant, thundering V8s with more than 400ci (including the 421ci, 428ci, and 455ci V8s) there is no such thing as a "big-block Pontiac" engine. This is because their V8s, from 326ci up to 455ci share the same external dimensions, with the later 301ci engine being a totally different animal that doesn't share much with its more famous brethren. 


So how does this relate to the lads big-block swapping 2SEXY and the Midget? It really doesn't: Marty and MOOG are using the term as a tongue-in-cheek reference to larger engines from the same manufacturer, which is in the spirit of the original way big-block truck engines ended up being slapped in passenger cars.   



Leave a comment

Please note, comments must be approved before they are published