i think a 402 bored .030 is actually around 408 ci- which you could round up to 409 if you wanted to get some old school badges for the fenders or something.
Chev bored the 396 .030 over from the factory for some reason in 70 or so- probably because they couldn't have the big small block (400) be bigger than the small big block (396).
i remember a magazine that did a comparison of a 400 small block and 402 big block built as identical as possible- same bore and stroke, same compression, same lift and duration, same style intake, same vintage heads, etc. the big block made more power and a lot more torque than the small block, but weighed like 200 pounds more and cost more to build.
i think they even put the engines in the same car back to back, and the big block was quite a bit faster.
wish i could remember the magazine- i'm thinking Hot Rod about 8-10 years ago.

 

396 and 402 ae basically the same except the bore size. As mentioned above Chevy sent them out from the factory that way (402). When you say 400 that is a small block.

 

Alright... thanks for the clarifications guys.

Now, for a really stupid question that I'm sure has been asked by newbies a million times (or at least WANTED to ask).... bare with me!
What makes a SB a SB, and a BB a BB? I know the usual, easy-to-see differences. Hence the reason one's called small and the other is called big.

Bore and stroke..... small or big. Same bore\stroke.... one's big and one's small?? This is where I'm confused.

Is it strictly the physical block\head mass, or what? Why is a 4.125" bore and 3.75" stroke in a 400 Small Block not the same thing as the same size bore and almost the exact same stroke in a 402 Big Block? The pistons are the same bore, the stroke is almost identical. Is it physical crank shaft dimensions, rod dimensions, head mechanicals dimensions, that make a BB bigger? And why are big blocks\heads so much beefier and larger in dimensions than small blocks\heads?

I just don't know enough about the physical differences internally that make a BB a larger hunk of iron (or aluminum).

That age-old 400 small block, big block thing again. I'm just trying to wrap my head around all of this for my own benefit. It'll help me "build" or at least find the right engine for my project.

Thanks

 

'Big Blocks' are - well "Bigger" - but, not necessarily "Larger"...

I get into lots of discussions with people I build engines for on what they should build for their car - be that a small block or big block.
I once heard Grumpy at a SEMA show explain that the 'cheapest & most reliable HP addition is Cubic Inches' - I have always agreed with that statement and followed his advise when going for more performance from an engine. I try to start with the largest displacement available for the given vehicle (or within the rules) and go from there - never leave extra cards on the table!
In the case of your project - I would have to know your budget, what driveline your car originally had (if it is to be part of the project) and what uses you intended for the vehicle.
If you have a Big Block car (or access to all the mounts and parts), a stout driveline (or the funds to install one) and are looking for a fun cruiser to 'WOW' the troops with I would say go with a Big Block.
If you have a Small Block car (or a 6 needing surgery) and a modest driveline budget and intend the car as a driver/cruiser then I would lean towards a Small Block with the mods to support your activity level. Small blocks can be reliably built that displace well over 400 CI - but I know of no law that says you have warn others by changing your 327 insignias

Hope some of this helps;

John

 

Ok, correct me if I'm wrong...

Smallblocks had a 4" bore spacing

Bigblocks had a 4.5" bore spacing.

Bigblocks use splayed valve heads, smallblocks do not (Without special hardware! Yes its out there..) Bigblock heads will have the valves visibly angled from one another ( like this \ / ) where smallblock valves are parallel (Like this | | )

 

BusDriver....

That bore spacing between the two is getting closer to what I'm looking for. Is there a reason the spacing is .5" more in a BB?
WHY is a big block bigger? Larger water jackets\oil galleys?
Why the bore spacing difference if the bore and stroke are the same?

**I know, I know... SHUT UP JOE!!**

 

The 400 SB has the center two bores on each side "siamesed", without a water jacket in between. So, I would say yep on the "larger" water jackets for the same bore (anything is bigger than none).

 

Right... BB & SB are completely different engine families...like comparing an olds to a pontiac, both came in a 350 and a 455, but not a single part will interchange.

All small block V8's share the same basic dimensions. Main bearing and bore spacing, deack height, bolt patterns, etc. you could scatter all the parts from a 302, 327, 350, & 400 in a room, and bolt 4 engines together without regard to where the parts came from. (no, they wouldn'tall work) All small blocks were produced on the same or similar foundries and production tooling.

Exactly the same is true of the big block family, but they are different from small blocks.

 

WHY is a big block bigger?

O o Which letter is bigger? Why?

 

onovakind67 I'm not falling for that optical illusion. You want me to say the first one is bigger, but it's really the second one!

Joe there was a 400 cubic inch limitation on GM intemediate passenger cars that was lifted for the 1970 model year. You could get larger displacement engines ordering COPO cars, but not RPO in those bodies. Anyway in 1970 they then punched the 396 out to 402 cubic inches. Why they continued to call it a 396 was probably a marketing decision since they already had everyone thinking 396 from the previous years performance passenger cars. There is probably more to this than I've offered here, but from what I've read and understand they couldn't offer RPO engines larger than 400 cid in those bodies until 1970.

The reason the BB is bigger is someone at Chevrolet wanted to go faster than the outdated fifties design SB would let them. Although Chevrolet didn't participate in racing officially at the time. They already had a big block in the 348 and 409 engines, the new style heads however is what really got things going, welcom the mystery motor. It was for sale a couple years ago at Yunicks shop sitting there on a pallet.

[ 09-16-2004, 06:09 PM: Message edited by: SY1 ]

 

OK, see if I have this right then....

A BB engine is simply just bigger in ALL respects: the cranks main journals, rod journals, rods, cam journals, combustion chamber, valvetrain, internal cavities for water and oil, etc. etc.
EVERYTHING is just larger dimensionally.

An engines "cubic inches" are determined by the combustion chamber volume at BDC. So if a 400ci SB and a 402ci BB engine have the same bore and basically the same stroke, the things that make the 402 a Big Block are all of the physical sizes of all of it's parts? It's simply "bigger"?
That's it?!

 

just take a look at a big lock in a car, then find a similar car with a small block in it.. you will then understand what makes a big block a big block and a small block a small block.
don't even ask what makes a Mopar big block a wedge or a Hemi...

 

Well, see Derrik, that's where I'm coming from. I was just looking deeper than physical size. It's more than plainly obvious when there's a BB under the hood...
I was just wondering why it would be bigger when all else is the same (bore\stroke).

I've had my fill. Thanks for the replies all.

 

Right.

The larger bore spacing and higher deck height allow for a much larger maximum bore and stroke than the small block design.

They made a 396 because of the 400 cube corporate limitation discussed above, in a block that could easily go to 500 cubes.

 

OK, I know you haven’t had enough Joe. I have a 72 Chevy with a 402 BB under the hood. This is the original motor for the truck, along with everything else (the pleasure of buying from an elderly man). Anyways, I found that the 402 was mostly offered in 72 because the 396 had proxcidity (sp? : means minute holes on surface after machining) in the cylinder walls and GM had to bore the blocks .030 over. That’s why they were offered for a short time. Please correct me if I’m wrong, but this is my understanding.

 

You guys are all wrong. A big block is bigger because it weighs more.

 

But then Gary you've got the odditiy of the ZL1, does it weigh more? Is it still a big block?

Like Onovakind67 said........O o which one is bigger? Why?

Joe just carry a small block head around for 5 minutes, then try the same with a big block head. You'll see Gary is right. You can prove it by measuring the length of your arm after carrying each for 5 minutes. If your knuckles rub on the ground it's a big block. This test doesn't work if your knuckles rub on the ground before the test, like a Mustang enthusiasts does for example.

 

Ok, here comes an answer from someone that does not know ANYTHING from engines

I think the BB is indeed made to make a 'fresh' start to make more cubic inches. A BB can make more HP/TQ than the 'same' SB setup. I think it also has to do with the V-shape of the engine.
SB 60deg(?)and the BB 90deg(?). If you have the pistons running vertically, you will have only(mainly!) a force running upwards and downwards (gravity etc.) which is an enormous stress on an engine! Just think about it, 6000rpm=100 reciprocating(sp)movements each second When it is finally at the TDC, it is being pulled/pushed downwards with an enormous speed/force. A 60deg V-engine will have, lets say, a 66% vertical force and 33% horizontal force. The horizontal force will be much less stressful for the pistons as it will run much more easily (due to other forces)
Therefor a 90deg engine will have a 50% vert and 50% horizontal forces.

Just look at other cars that use the Boxer principle (horizontal running pistons), Subaru Impreza GT Turbo, Porshe Boxer, several Alfa Romeo's etc.

To guess answer the question to your question Joe, A BB is bigger because the 90deg V-shape needs more metal to fill the gaps and to make it look 'more'...... just a guess!

 

Now there's an answer I can sink my teeth into!

2 good answers so far..... bore spacing and block angle.

 

Okay Joe you asked for it. Grab a beer and settle in this gets a little lengthy.

Besides the small block 265 and 283 Chevy also had a 409 big block motor, before that a 348 W block big block motor. In 61 a 409 Impala was the winner at the NHRA Winternationals. Also in 61 Dan Gurney set a track record in a stock 409 Impals tearing up the old record held by a fuel injected 283 Vette. The stage was set for bigger motors than the small block package currently offered.

Now go back to 1957. chevy engineers realized with the heavier 58 models coming in they needed more engine than the 283 to be competitive, chevy was still officially racing cars at this time. At that time they had the bore and stroke to build 302 cid but that was their limit at the time. So they reluctantly began hopping up the W block 348, a truck motor primarily at the time. Maurice Rosenberger formerly of Cadillac was awarded the task of making it run with wild cams, multi carbs and high comp pistons. Assisted by Fred Frincke and Dennis Davis they turned to building more cubes and the 409 project began. It was suppose to be a bored out 348, but ended up with only a few interchangable parts with the 348. They shared blocks and deckangles, but the 409 required shorter connecting rodsand ended up with increased max rod angularity and side thrust loads on the pistons. They shared cylinder head castings, but some of the machining was different, the 409 had wider pushrod holes and different valve spring pockets.

In the quest for speed championships in 63 the Mystery Motor 427 appeared at Daytona and blew everything off the track before dropping out due to an engine failure. This engine was for sale at Smokey Yunick shop a few years ago. Work continued on the motor at the Warren Tech Center back in Michigan. In 65 it was offered as a 396 by Chevrolet. There were many people involved with the developement, but the design of the porcupine heads goes to Robert Benzinger. He had designed the Corvair all aluminum flat six and was one of Chevys top engine tech men.

His approach was to design the motor backwards. Normally an engineer starts with the combustion chamber shape and arranges the valves to operate as simply as possible. He decided to focus on the breathing first and started with the ports and manifolds. I've got to believe that Smokey had a big influence here, he had the state of the art flow benches which is why Chevrolet took many of their experimental parts to him to evaluate and tweek. Benzinger got the flow characteristics where he was happy and then built the rest of the motor around it.

Tonawanda's plant was due for retooling when the 409 was barely 5 years old. The 409 was tooled for low production and Bunkie Knudsen the GM at the division decided if they were to retool only the most modern engine was justified to continue production. The 409 died it's death and the Mark IV big block was born.

Even though the small block was bored out to 4.125 inches in 70 the 400 was never considered as a high performance engine due to the thin cylinder walls and the lack of cooling jackets between the cylinders, along with the shorter con rods. So the BB got the nod in hi-perf applications.

A lot of this info came from Hi-Performance Chevrolet by Richard Langworth. It's a pretty good book to read.

You can see the BB vs SB goes back way before the 400 was ever in the picture. I thought it was interesting how the 409 met it's fate, it was a coporate bottom line decision, nothing to do with the performance of the motor, it was just felt the future was in the new Mark IV.

 

Originally posted by DL:
Ok, here comes an answer from someone that does not know ANYTHING from engines

I think it also has to do with the V-shape of the engine.
SB 60deg(?)and the BB 90deg(?). ...... just a guess!

All small and big block chevy engines (the ones we're talking about here) have their bores angle 45deg from '0' center making them a 90deg design.
Their are some 60deg. GM V-6's floating around out there...
Looks like the apple missed you on this one Newton...
Gravity is important in our everyday lives - but not to our engines, except that they are trying to overcome some of it's forces to propel our cars down the road.
A well balanced engine doesn't give a squat about the effects of gravity on it's rotating mass.

 

Vintage, I told you I know nothing about engines but I wasn't referring to gravity on its own, but on all forces on the piston (therefor also gravity)

I should make a drawing to explain more easily, but finding the exact technical words in english is sometimes difficult for me (I'm Dutch)

Anyway, I don't know the exact angle of the SBC and the BBC, but there is an angle differance. This is what I am trying to explain. Forces are aplied in every direction, gravity (as an example) is one force pointing to the ground. Other forces (due to combustion, friction, etc.etc.) can be translated into Horizontal forces and Vertical forces. 45° force is 1Hori, 1Verti, sqrt2Diagonal ..... a 30° force is 1Hori, 2Vert, sqrt3Diagonal meaning there are more vertical forces on a 30° engine-side.

A boxer-engine has almost no vert forces except gravity.

Like I wrote before, I'm not an engine expert (I think there are 5 V8's running in a circle of 200mls from me )
BIG MISTAKE OF ME THINKING A BBC AND SBC HAVE DIFFERENT ANGLES INTERNALLY

LOL, I've learned something today

 

what different angles are you talking about that seperate a small block from a big block? they both have bores that are 90 degrees apart. the valve angles are different- but a big block is still only a big block because it's physically bigger than a small block...

 

I luv Smoky Yunick, he was the absolute God of motors.... I remember a magazine article when I was a kid, he had a small block running with no cam, used soleniods to open and close the valves, a giant cumputer to run em... totally variable valve timing, optimum at every rpm.... nuttin like it since.

and no, that has nothing to do with big blocks, which are by the way, bigger.

 

LOL! Jim

"My car crashed today.... I had to reboot it twice!"