What’s in a Name? The Simple Difference Between a Small Block and a Big Block

When you get into the world of GM for the first time—usually at the tender age of old enough—you get introduced to the vast world of their engine block selections. As you grew up you kind of had a general understanding of what a big block was and what a small block was. Well, you did until you saw your first 400-cubic inch small block and 396-cubic inch big block. “How can something be over 396-cubic inches and be a small block?” You probably asked yourself. Turns out, there is a very simple reason.

First, if you’re an engine builder or someone who’s been around the, erhm, block on GM engines, this is going to, uhh, bore you. (These puns are a stroke of genius – .ed) Anyhow, to you guys this will seem like it’s obvious. However, for you new guys just getting introduced to GM, “Big Block” and “Small Block” are not determined by their displacement. It’s the engineers that determine if an engine is a small or big block by its physical size. A big block is literally bigger than a small block.

As you see in the video, it’s not just in the block but the head as well.

This video also gives you a great little nugget of extra information on head design by talking briefly about a canted valve. If you’ve never built an engine and heard this term before, you just gained some extra knowledge.

The all-new LSX 454 crate engine uses LSX forged rotating parts and a newly developed 0.635-inch-lift hydraulic roller cam, making this a monster LS engine in a classic cubic-inch combo. Through its four-barrel carburetor, it’s rated at 620 horsepower. X09SP_PA014

So, with that being said what are the LS-series and the new LT-series considered? Well, even as they gain cubic inches GM still considers both series as small blocks. Yes, this even includes the GM Performance LSX at 454-plus-cubic inches, but the ZZ502 and the ZZ572 are big blocks.