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Engine terminology? Big block/small block/short block/long block

I hear/read those terms when talking about engines and engine rebuilding, but I don’t know what they refer to? Anybody know?

Short block means just the engine block with the crank, rods, pistons, cam shaft and timing chain set. A long block means a short block with the head(s) and push rods and lifters.

A small block/big block designation is from GM engines. A small block was called a mouse motor and a big block was called a rat motor. The lines were blurred between a mouse motor and a rat motor. But it basically came down to how much power could be produced from the motor based on the weight of the motor.


The terms long block and short block refer to how complete the engine is. The completely assembled lower end (block) of the engine is called a short block. Any engine with the heads installed is a long block. Domestic V-8s, especially Ghevrolet, offered large and small block engines that differed in the basic dimensions and the running dimensions. The details are likely more than you want to know but although displacement is the significant dimension, there are small block 400 ci and large block 366ci engines. The Cehvrolet small blocks range from 260 to 400 and big blocks from 348 to 454, as best I can recall. There is a significant increase in the size and weight of big blocks, though.

When buying a replacement engine rebuilders offer the option of buying the short block or long block. It is usually much cheaper to use a short block and install the old heads if they can be easily cleaned up (valve job).

I will just add something else to muddy the water a bit more. With the abundance of performance parts available now (and using Ford as an example) one can have a 390 cubic inch big block and 428 cubic inch small block. The latter is a 351 with a stroker kit.

This carries over to other makes also. One can have a 396 CI Chevy big block and a 427 CI small block.

Some guy back east who specializes in race engines recently unleashed a 1000+ cubic inch block. :slight_smile:

I agree with everything said so far…but to add a little bit more.

GM had a Chevrolet 350 small block and a Pontiac 350 big block.

While displacement was the same…the overall outside dimension of the Pontiac 350 was a Big Block.

I think short block/long block has been fairly covered.

Big block/Small block refers to overall size of the engine block. Ford, Chevy, and Mopar (Chrysler) have engine designated as big blocks and small blocks in various displacements. The big difference is that big blocks are very heavy, but tend to develop a lot more torque due to the larger size of pistons and larger stroke of the crankshaft. These usually find themselves in trucks, but were used in muscle cars in the 70’s for large amounts of power. Small blocks are dimensionally smaller and lighter and can produce plenty of power for most large cars and perfomance cars. Big blocks have just about disappeared in new cars and trucks due to fuel economy and emissions requirements. Plus, modern technology has improved small block power to big block standards of the 70’s and 80’s with much improved fuel economy and emissions.

Some common displacements:
Chevy small block: 283, 307, 327, 350, 400 (most common ‘crate motor’ is a 350)
Chevy big block: 396, 427, 454
Ford small block: 260, 289, 302, 351 Windsor
Ford big block: 360, 390, 427, 428, 429, 460 (but various base engines, I think)
Mopar small block: 273, 318, 340, 360
Mopar big block: 383, 400, 426, 440
Many other displacements, blocks, etc over the years, sure I made some errors.
Only modern engines (sold in current cars/trucks) are the Chevy V8s that trace back to the small block and big block, I think.

If you’re curious Wikipedia has extensive articles on all the different engine families.

p.s. - Just looked in Wiki, turns out several of the ‘big block’ Ford engines I listed are considered ‘medium block’ engines by Ford. First time I’ve heard of that!

There’s a local guy here who works wonders with small block Fords and runs them on Ethanol. His late model Mustang (or what’s left of it) is on display at his shop. It went airborne at over 260 MPH on the Bonneville salt for a 1000 feet before tumbling end over end.
He’s also got a way cool late model Crown Vic that hit 160 MPH in 4th gear before blowing up; and he still had 2 more gears to go in the manual gearbox. That one’s in the process of being done up again.

His diesel pickup has hit 182 MPH and he’s got the record on that one. Amazingly, if the stickers were removed along with the roll cage and fuel cells, one would think the truck is bone stock by looking and listening to it.

It’s pretty fascinating what technology has managed to do with fewer cubic inches.

You can go back to the flathead Chrysler 6 cylinder days of the 1940s through the mid 1950s to see two different block sizes. The Plymouth and Dodge used a smaller block and the displacement was 218 cubic inches for the Plymouth and 230 for the Dodge. Thee was a larger block for the DeSoto and Chrysler. The displacements were 236 cubic inches and 250 cubic inches.

Comparing a bare Ford 302 to a 390 makes the term big and small blocks very obvious. But the
V-8s may be phased out in a few years for all but medium duty trucks as fuel mileage demands make them obsolete. Two and 3 cylinder engines may become the norm in sedans soon.

@ Rod Knox

2 and 3 cylinder engines in North American cars aren’t going to be the norm any time soon as they tend to get worse mileage than the larger engines. For example Ford sells a 1 liter Ecoboost 3 cylinder version of the Focus in Europe. It gets the same real world mileage as the naturally aspirated 2.0L I4 used in the North American Focus . Likewise Fiat makes a 2 cylinder 900cc (I think) version of it’s small Panda city car. It’s real world mileage is substantially less than the diesel engines fiat offers for the Panda and also less than the larger 1.2L petrol engine offered.

With that said, I do see turbocharged fours being used more in the North American market, as well as direct injected, high tech fours. V6’s will still be around, but they won’t be as common. I also see diesels making some headway as well. Unfortunately for some of us big displacement muscle cars and sports cars will go up in price.

There’s another term you might hear on occasion: “crate engine”. Generally a crate engine is considered to be an engine that’s ready to install. While a “long block” includes the heads and valvetrain, it doesn’t include the induction system, exhaust manifold(s), alterator, etc. necessary to complete the engine. A crate engine does.

Pics (all small block Chevys):
Short block-

Long block-

‘Crate engine’ (note no alternator or exhaust manifolds, that depends, also this seller calls everything a ‘crate engine’, short and long blocks included. This they call a ‘turnkey crate engine’)-

I think of these when I think of a crate engine.

But I gotta admit that even some of these are less complete than I suggested. Perhaps I over-stated.

         ok4450       " one can have a 390 cubic inch big block and 428 cubic inch small block. The latter is a 351 with a stroker kit."   You might be able to build a 351 up to 428, but a factory 428 was a BIG block.

Thanks everyone for taking time to post. Great explanations.

Car terminology can be confusing for the amaeture driveway fix-it-yourselver. One time I was removing a power steering pump from my 70’s Ford truck to get at the fuel pump – well, that’s a whole 'nother funny story – anyway, the Chilton’s manual said the way to do it was to “use a jam nut”. I wondered and wondered what the heck a “jam nut” was. Seriously, I thought and thought about this. … lol … Anyway, I never actually figured it out for certain what it was, but always willing to move forward even when I don’t know what I’m doing, I noticed the pump was held on by – not a bolt – but a threaded rod, and at the end of the rod there was a nut which was pretty rusted, so it stuck to the rod. I was able to remove the threaded rod from the block just but twisting the nut with a wrench. But if the nut wasn’t rusted on, then I think I’d probably have put another nut on there to make the nut not move. Then I thought to myself, I wonder, is this what a “jam nut” is? i.e. just two nuts back to back so they don’t move if you want to twist the threaded rod, not the nut?

The small block/big block dofference is cylinder bore spacong. All small blocks from one manifacturer will have the same spacing and rhe same for the big blocks. They can vary the bore and stroke but not the spacing. If they change the spacing they create a new engine family,
Ford may have considered some of their 400+engines " medium block " because they made gasoline V8 engines in 477 and 534 inch sizes for trucks.
Chrysler used 3 different block sizes on their early V8 engines of the 1950s. Dodge and Plymouths got the small block (generally) DeSoto got a medium block and Chrysler got the big blogk.

@GerogeSanJose - yes, that’s what I call a ‘jam nut’. I had to use them to retighten some boltls that came loose. I could only (easily) get to the threaded part of the end of the bolt, so I ‘jammed’ two nuts together to tighten the bolt, then used one of the nuts as a lock nut.

OK,sure would like to hear more about this smallblock Ford guy-good posts people-Kevin

oldtimer 11 If you increased the bore, wouldn’t you shorten the space between them. And also if you had a larger space between bores, wouldn’t that make for a longer (bigger) block??