Big Block vs. Small Block

[Ross]

We all use the terms "big" block and "small" block. Is there some actual dividing line between the two? I know that our 4.6L engines are small block, and an old Ford 390 would be a big block, but where do you draw the line? Is a 351 big or small? What if you bored out a 4.6 to make it a 5.0 or bigger? You would have more displacement, but the block would still be the same size. Help me out with the terminology, please.

[67435animal]

The 351 would be a small block as I recall. Boring a small block does not morph it to a big block.

The designation is based on the displacement when originally manufactured.

Let me relate it in terms I know better. Chevrolet makes a small block and a big block The SBs are 265CI, 283CI, 327CI, 400CI and 350CI. The BBs are 396CI, 427CI and 454CI.

The Chevy SBs are all based upon the same basic small block design. The big blocks are all based on the same design.

Hope this helps a little. My avatar is a 427 BB.

Bob

[Ross]

Thanks, Bob. The Chevy designations are what have thrown me for a long time. I know that the 400 CID (which I used to have in a beautiful '76 Monte Carlo) is a small block, while the slightly smaller 396 CID is a big block. Therefore, it can't be the displacement that determines small vs. big. So it always made me wonder, what is the difference?

[67435animal]

The actual block casting itself. It may be bored differently for various applications but it is still the same physical block.

Bob

[Ross]

Gotcha! Thanks for the help. Is FoMoCo currently using any big blocks?

[Macon Marauder]

The last FoMoCo big block that I can remember was the 460 which "disappeared" in the late 70's. Same block as the 429 I believe.

I've seen a few big Ford trucks with "370" on the grills. Don't know what that's based on.

[TripleTransAm]

It all has to do with the actual size of the block itself, not the displacement. Stuff like deck height, wall thickness, etc. Most US V8s start out with a 90 degree 'V' angle, so the difference is in how much 'width' the engine takes up.

The larger blocks will obviously hold a larger bore and possibly a larger stroke. That's why they tend to develop larger overall displacements.

Chrysler even had the same displacement across 2 engine families, I think. They had the 318 small block (lasted throughout the 60s 70s and 80s) but for a brief while in the mid to late 60s, they also had a 318 cubic inch version of the bigger block (the one that eventually grew to 361, 383, and with an increase in deck height, the 413, 426, 440 etc.).

[RF Overlord]

I had a 7.5L (460) in my '95 E350 bucket truck...so it was sometime after that they dropped it...

Point of interest...sometime in the mid to late '70's Chevy actually made a 400ci small block AND a 400ci big block, which was also called the 402...

[TripleTransAm]

Early 70s... the 400 was a stroked small block, I think (not much more meat left to bore out) that was available in a whopping 2 Bbl configuration as a "big" small block for the Impala, Caprice, etc.

The 402 was an expanded 396 big block. In fact, they marketed it as a 396 for some reason. Available at least in Camaros until 1972 I think, in the SS396 package.

[BillyGman]

car manufactures had two different V8 engine blocks(Big block, small block). To my knowledge the exception to that rule was Pontiac. I believe ALL Pontiac V8 engines were at one time big blocks. There was the 326,389,400, & 421 cubic inch engines, which all used the same block.
When it comes to Ford, they had a 351 small block, and a 352 big block in the 60's. In addition to the block sizes being different, the cylinder heads for the small and big block motors were usually different. And ofcourse the big block heads had better airflow rates, which enabled the engine to breath better and therefore produce more HP. So for instance, a 402 big block Chevy motor produced more HP out of the factory than the 400 chevy small block did even though the cubic inch displacement was about the same simply because the 396/402 motor had the big block cylinder heads which had bigger intake runners, and offset, or splayed valve angles which gave them better airflow capabilities which in turn means more HP. Personaly I really wish the car manufactures would revive the big blocks. And I don't mean some weed wacker sounding V10 engine either. But some big block V8 power. The one biggest problem probably is the emission standards which is all a crock. Why do I say that? I just got through installing the Kook's headers on my Marauder. And it made me laugh to have to screw on the pipe coming from the air pump to the headers. What a joke. So in order to get around emission standards, the car manufacture has to engineer a pump that will pump air into the exhaust AFTER it exits the engine to change the percentage of Hydrocarbons to oxygen coming out of the tailpipe simply to get the car through an emissions test. Ofcourse all of that does is to dilute the Hydrocarbons that exit the tailpipe. It does nothing to reduce the HC's from entering in the earth's atmosphere. Meanwhile you have diesel cars belching out soot into the atmosphere. It's all a big game, and it's all about money for the state. But I guess I got on a roll there. Please excuse my rant. Didn't mean to get off the subject of BIG BLOCK engines which happens to be one of my favorite topics!!! There's nothing like the growl of a Big Block V8 engine. It's ALL macho. The true sound of power.

[jparrie]

Actually the function of the air injection pump is to allow for more complete (cleaner) combustion. By injecting oxygen into the stream of superhot exhaust gases, they continue burning longer than they would without the o2.

Much the same way that an ox/acetyline torch burns hotter and cleaner as you add o2 to the mixture.

Jim



Originally posted by BillyGman

I just got through installing the Kook's headers on my Marauder. And it made me laugh to have to screw on the pipe coming from the air pump to the headers. What a joke. So in order to get around emission standards, the car manufacture has to engineer a pump that will pump air into the exhaust AFTER it exits the engine to change the percentage of Hydrocarbons to oxygen coming out of the tailpipe simply to get the car through an emissions test. Ofcourse all of that does is to dilute the Hydrocarbons that exit the tailpipe. It does nothing to reduce the HC's from entering in the earth's atmosphere.

[TripleTransAm]

Keep in mind that this O2 injection only happens during open loop operation, otherwise the added oxygen in the exhaust stream would fool the PCM into thinking it was running too lean.

So, when the car is cold, the air pump is pumping air into the manifolds/headers in order to keep the mixture burning, so to speak, for (I think) two reasons:
1) keep a hot exhaust to 'light off' the catalytic converters as fast as possible, as they don't work at all when cold.
2) the cold mixtures are much richer for atomization reasons, so this would kill a converter in no time unless they were burned off before reaching the cats. Ask me how I know.

Once the engine reaches closed loop temperatures, the air pump shuts off, at least in modern air injection systems. On my GTA, I'm not sure if it then begins to divert air to the catalytic converter to continue the chemical reaction in there. But on my WS6 I know the electric air pump completely shuts off altogether.

So, no, it's not to 'dilute' the exhaust...

[BillyGman]

but I didn't think the air pump was electric on many vehicles including the Marauder, since it's belt driven. Right? Or does it have a clutch on it like the A/C compressor does?

[FordNut]

How about let's muddy the water a little more. Ford has made 4 different engine families of pushrod engines in modern times. The 260, 289, 302, and 351W are small blocks, of the Windsor family. The 351 Windsor is a small block design but the deck height, crank journals, and other small details are different from the rest of the small blocks. The 351C, 351M, and 400 are neither small blocks or big blocks. They are actually an intermediate size, the Cleveland or '335' family. The 351 Cleveland uses the same bellhousing as the smallblocks, while the 351 Modified and 400 use the '385' series big block bellhousing and have taller deck heights than the 351C. The 352, 402, 427, and 428 (and other odd sizes) are the older FE big block family. The main differences are internals (bore/stroke) with minor differences (side oiler/center oiler, etc) in some of the blocks, heads, and intakes. They have their own unique bell housing not shared with any other engine family. The most unique block is the 427 side oiler, which has larger cylinders than the 428. The other big block is the 429 and 460 engines, the '385' family. Most parts are interchangeable between these two, the stroke being the main difference.

So we have a 351 small block, a 351 intermediate, and a 352 big block. We have a 400 intermediate and a 402 big block. We have a 427 and 428 big block of one family and a 429 big block of a different family.

Chevy has done some similar things, as there are 2 different big block 427 Chevy engines, one was the old 348/409 block and head design, the other being the newer 396/427/454 design.

[BillyGman]

good info there........I think that by the mid 60's Chevy became kniwn as having engin packages that were a bit more versatile as far as the interchangeability of part went. But ofcourse that's all different now. These days w/all these computer generated and aerodynamic body style designs, your lucky to find a car that looks good that has a V8 engine under the hood, let alone any big block design. Can I say it again? I really have a disgust for this trend of moving towards a V-10 engine design for Big performance. And I don't care what the reasons for that are. Nothing sounds like a V8. And that's just one of the things I LUV about the 2005 Ford GT. Gimmie that V8 growl any day!

[TripleTransAm]

Great post, Fordnut. Gotta add that the Chevy 427 based on the 409 didn't really appear in too many cars in 1963... I think it was limited to factory drag racing teams only, so very few made it out there, considering the end of GM's racing involvement that year. The 427 Mark II on the other hand was oval-track only (Nascar) and eventually lent some design cues to the 396/427/454 Mark IV family of big block.

Great details on the Ford engine family, really appreciated. Never realized they made a 402. (or actually, do you mean a 406?).

Gman, air pump is electric on my WS6, belt driven on my GTA (w/ solenoids for bypass control). No idea about my Marauder.

[Mad4Macs]

Even better... Ford's 351W was considered a small block. The 351C, however, was a big block ;)

[Mad4Macs]

Whoops!!! I just re-read FordNuts post. Great job!!

[Dr Caleb]

Hee hee hee. He said "nuts". He He he.

[TheDealer]

A 351 Cleveland is considered a small block since it uses the same bell housing as a 289,302,351w. A 351m is considred a big block since it uses a 429/460 bell housing. But a 351 cleveland uses the same dist as a 429/460. So you figure it out. GM is the one that uses the term, small block and big block. Just like they call it a posi rear and Ford calls it a Traction Lock. I don't like to compare GM to Ford. We are different and I like it that way. RAY

[TheDealer]

Ford goes by engine families. There are 4.6 windsors, and 4.6 romeos. Windsor family, 221,255,260,289,302,351w. Boss 302's were windsor blocks with cleveland style heads. 335 family, 351c, 351m,400. FE family, 332,352,359,360,361,370,390,39 1,406,427,427SOHC,428.
MEL Family [Mercury,Lincoln,Edsel for 50's and 60's] 361,383,430,462.
385 Family, 429, Boss429,460.
All 5.4's are windsors. I'm sure I forgot some. Ray

[Ross]

I ask a question on this board and learn more than I ever thought that I would! Thanks for all of the info, guys. There's a heck of a lot of experience and knowledge around here.:rock:

[TJH]

As others have noted, the "big block"/"small block" thing can really best be applied to Chevy. Until the modular V8's and V10 came out, Ford also had small and big block configurations that more closely match the definition, without the muddying of the waters caused by the 351/400M and the like.

With respect to the Chevy, the naming convention does NOT pertain to all other GM divisions. I cringe every time I see/hear someone refer to a "big block" Pontiac. There is no such animal. Nor is there a small block Pontiac V8. ALL Pontiac V8's share the SAME external dimensions, and also (with the exception of the 301) the same connecting rods. Heads will all interchange. A 350 crankshaft can be used in a 400. Intake manifolds will all interchange. So will all accessory drives, fuel pumps, timing chain covers, distributors, etc. The Pontiac V8 is a Pontiac V8- the displacement may be big, but there is no such thing as a "big block" Pontiac, and those that use that term are only displaying their ignorance of the architecture.
What there IS, in the Pontiac world, is small and large-journel crankshafts. All of the engines except the 421, 428, and 455 use a 3.00 inch main bearing diameter crankshaft, whereas the 421/428/455 use a 3.25 main bearing journel diameter.

As for the Ford big blocks, the last production 460 was used in the F250-up in 1997. I had a 1997 F350 4X4 with the 460, and loved it. Unloaded or pulling a 10,000 pound trailer, it was always 12-15 MPG. When the P131 SuperDuty trucks launched in mid-1998), the V10 6.8L was the largest engine offered, and it is part of the same "family" that our 4.6L 4V belongs to.

[BillyGman]

that's what I thught about the old Pontiac V8 engines....they're all the same block.

[TripleTransAm]

The only exception to the "same block" Pontiac thing is the 265 and 301 V8s, available in the late 70s and early 80s. These puny guys had thin cylinder walls and lower decks, and not much can interchange with them because of this, on the heads and intake side. Internally, I think there is some interchangeability.

But as was mentioned, everything else *could* be interchanged, as long as some year-specific compatibility was respected (ie. you can't put a '63 intake on a '67 head or something like that, I can't remember the details, but there are a few like this).