What makes a Small block a Small block and a Big Block a big block?

[gtsr515]

I've put basic motors together for years, but I'm no Jack Roush type engine builder supreme.

My question is as stated above, what determines a "blocks" status, we hear of 427 "small blocks", but normal "thinking" or "stereotype" this would be a "big block".

Can anyone clear up my ignorance?

For instance, I have a Lingenfelter parts catalog that has a "427 small block, twin turbo package."

[PKRWUD]

It's just what the name suggests; the size of the block. It's confusing to some, because of ads like the one you mention, but they refer to displacement. You can over bore and stroke some small blocks in order to achieve larger displacement figures, and in fact the factory does that themselves. Take for example the Ford 400M small block, versus the 390 big block. The 400 has more cubic inches, but the 390 is physically bigger. Where this really gets confusing is with Oldsmobiles. Their blocks are all the same size, except for the cylinder height. That is all that separates an Olds big block from an olds small block. The benefit is that most Olds parts, from a 330 to a 455, are interchangable, except for the intake manifold, and on older blocks, the cam & lifters.

Take care,
-Chris

[PKRWUD]

As a footnote, there is also always forced induction. People often misunderstand exactly what a blower does. It's really rather simple. It does one thing, and one thing only, and that is to increase the displacement of an engine. What's cool, is that it can do it to any engine, without changing the bore and/or stroke. For example, at sea level, a 302 that has a blower actually has 604 cubic inches of displacement when that blower reaches 14.7 pounds of boost (14.7 psi is the atmospheric pressure at sea level).

Take care,
-Chris

[gtsr515]

Okay Chris, gotcha, I knew you would be all over this one, in vane with the blower/displacement increase thing?..........what would you say my 302, bone stock heads, cam, and intake wise, on 150 horse of spray was "displacing" at that time, screaming down the track?

[PKRWUD]

Nitrous is a different animal, it doesn't increase displacement. Nitrous oxide is simply a method of adding oxygen to the mixture in a controlled manner. The burnrate of the oxygen is controlled, whereas any other method of adding oxygen is uncontrollable, and would literally explode the engine. In the "old days", people who couldn't get nitrous would install a water injection system. That was another method of increasing the oxygen content in the mixture, but it was also very dangerous because water won't compress, and if too much was injected, the engine would hydro-lock.

Take care,
-Chris

[gtsr515]

HHHHHHMMMMM, okay, let me ask you this then, you would agree that both Supercharger and Nitrous, (and blower) increase "compression" right, so how can Nitrous not increase displacement and a supercharger would, is it because a supercharger is using "air" and nitrous is just changing the air?

I dont get it?

[Jeb_Bush_2000]

The displacement of an engine is strictly the amount of air it consumes when it makes one revolution.


A blower pushing 1 atmosphere of boost crams -- in theory -- exactly twice as much air into an engine as an NA one.

[PKRWUD]

Nitrous does not increase your compression, it makes the mixture being compressed more powerfull by increasing the oxygen content. Technically, a blower doesn't increase your compression either. It compresses the air before it reaches the cylinder(s).

Take care,
-Chris

[Coupe5oh]

Well big blocks are, in most cases a way bigger cylinder bore, and sometimes a small stroke on the crank, not always, for example, take a 383 chevy, its a 350 with a bigger 3.75in stroke, and bored .030, and compare it to a bigblock chrysler 383, which is 4.25 bore, and small 3.36 stroke, and torque, what big bore, and small stroke created, was a high reving somebatch.

[Shogun]

Also, you must add more fuel if you add more air. Because the extra power really comes from the fuel, the extra air only helps facilitate burning. Without the extra fuel you will have severe lean condition and will melt something. Its all about hope much cylinder pressure you can safely generate without hurting your engines internals. my .02

[flyin 5.8]

I have an old school bus (laugh all you want) with a 360 or 361cid FE engine. Why does this statment not apply

"what big bore, and small stroke created, was a high reving somebatch."

Yes we did remove the governer (55-60mph on I-94 from k-zoo to jackson tends to tick people off) and it still only revs to about 3500rpm. any more and it throws belts everywhere.

[MidNiteBlu 5.0]

To answer your question flyin, I would guess that the engine in your bus is not a big bore short stroke engine. It seems to me that the engine in thier would be a truck engine that would make more low end torque to push that big heavy bus.

Truck engines and high performance car engines are usually much different.

Later,
Nick

[Unit 5302]

The 361 in the school bus is a 4.0469x3.500 bore x stroke. What kills it's rpm capability is a 2bbl carb, and 8.5:1 compression. It's not meant to rev, athough if there were to be a high po intake, better pistons and rods (the crank is already forged), and some compression, it'd probably wind over 5000 pretty easy.

Big blocks are heavy, bulky, and as a general rule high rpms meant 5500rpm-6000rpm. The 427FE was as rev happy as you could get in the FE line, and it redlined between 6000-7000rpm depending on how it was built.

There are several series of engines. External block dimentions were how they were designated big block/small block. Ford used a couple different sized blocks in the lineup for many years.

FE
385 series
MEL series

Those were the big blocks.

Y Block
Windsor or 90*
335 series

Those were the small blocks.

[Ponycar_302]

I have an old school bus (laugh all you want)

I actually didn't laugh until you mentioned it. I thought you were going to say you converted it into some sort of dragster.

Anyway, hey Chris, doesn't Pontiac just consider their blocks as blocks? What I mean is, there is no Pontiac small block or Pontiac big block. It's just a Pontiac engine known simply by their displacement.