I do not know much about big blocks can anybody tell me what make a BB a BB

 

Since my car only has a Rocket 350, I always assumed it was the engines that had over 400 CID. But, that's not apparently true. According to what I've read the 400, 403 and 425 were all small blocks. I also would like to know the answer. I suspect it's something to do with the V angle of the block, piston travel, heads and the larger CID. I don't think it is based on HP and torque, because a 350 can be engineered to put out some absolutely wicked power curves. I'm up for a schooling too! BB guys, c'mon down and impart your wisdom.

 

Here's my experience. The 330, 350, 403 are small blocks. The 400, 425, 455 are big blocks. The deck height (portions of the block where the cylinders are) is one inch taller on a big block than a small block. That makes the intake manifold and the whole top of the engine wider. That is the outside physical difference, but the internals have some differences too. I believe a 350 crankshaft is the same length as the 455, but the 455 crank is much beefier, bigger lobes for counterweights. I believe the main journals are larger on the big block but am not sure. I think that's true about all small block and big block crankshafts. That's what comes to my mind as differences, others will need to add to it with more details or clarifications. John

 

Small blocks GENERALLY had a 3.385-inch bore, while Big Blocks GENERALLY had a 4.126-inch bore. The difference between a 425 and a 455, both big-blocks, was the stroke, which was 3.975" in the 425 and 4.25" in the 455.

The small-block 350 was "oversquare" in that the bore was wider than the stroke was long (4.057" by 3.385").

But the 400, which was also a big block, was also oversquare with a 4.000" bore and 3.975" stroke in the 1965 through '67 version and very undersquare (3.87" bore and 4.125" stroke) in the 1968-1969 version. The later version is apparently less desirable from a power standpoint.

But as 2blu442 says, it wasn't just these measurements that distinguished a big block from a small block. Deck height did as well, with the 400, 425, and 455 being "tall deck" engines, while the 350 and 403 were "short deck."


I'm sure others will add more, and I wouldn't be surprised to hear that I've got some of the above wrong.

 

The deck height being taller makes them wider than the sbo. The crank on the sbo (except the diesel blocks) has 2.5" mains where the bbo (including the sbo diesel blocks) uses 3" mains.
260, 307, 330, 350, 403 are the sbo. 400, 400, 425, 455 are bbo. Yes I did 400 twice as there are actually 2 different 400 blocks that use different bores and strokes.
There was also a NASCAR block that is even more beefy than the diesel block, but that is VERY rare and from what I have seen there are even some special made ones with oddball main sizes.
Being that the diesel block uses bbo size mains you can use the steel crank from the 425 after some counter weight modification and have a nice stroker sbo.

All sbo engines use the same stroke. Al of the cubic inches are to be had in the bore. So the 260 uses the same stroke as the 403.

The bbo use different strokes and bores to achieve the cubic inches.

 

In addition, because of their greater size, the large blocks hurt a hell of a lot more when they roll over onto your foot

 

For those who did not know-

At the North and South Poles, they have engines that make the Earth rotate. They are Oldsmobile 455s, one driving normally and one thru a reversed gearbox. Nothing else has been found to duplicate the torque required to move a vessel such as Earth.







Hay, it's as good as explanation as any! and that is the difference between Oldsmobile big blocks and any other engine!

 

OK first, there is no "legal" definition of "big block" or "small block". Since the world is Chevy-centric, these terms have come to describe the two main engine families built by Chevy over the years. Chevy big and small blocks are completely different with almost no parts that interchange.

Olds motors are a little different. The 1964-1990 motors use pretty much the same architecture and therefore share lots of parts. The main difference is in the deck height. The 260, 307, 330, 350, and 403 are short deck motors and are commonly referred to as "small blocks" by the Oldsmoscenti. The 400 (both long and short stroke), 425, and 455 all have a taller deck (as well as larger bearings on the crank and longer rods) and are referred to as "big blocks". Parts like heads, cams, distributor, timing chain, oil pump, and even oil pans interchange between the two families. Since the small block Olds diesel motors used the big block sized main bearings, it is even possible to put a big block crank in a diesel block to create a large displacement small block gasoline engine.

In reality, the Olds "big block" and "small block" motor families are more like the short deck and tall deck Chevy motors or the B and RB engine families from Chrysler. The terms big and small block are just common useage today.

 

AWSOME! I knew there was a reason why we sent scientists out there. They have to add fuel every so often. I bet those Olds engines have Batten heads, and Port-O-Sonic intake manifolds!

 

Thanks. I figured that the terms were used as much on the basis of history and tradition as much as they might have been based on anything specific.

 

They especially like big-inch Olds at the North Pole. Santa Claus's preferred sled is a W34 Toronado.

 

Small blocks, except the diesel, have smaller mains (2.5") than the big blocks (3"). The definitive difference is the deck height, which brings about changes in rod length (6" vs. 6.735 or 7") and width of the intake manifold. Also, big blocks had bigger (taller) intake ports and longer strokes (3.975" or 4.25" instead of the small blocks 3.385").

 

 

Thanks. I had that backwards.

 

And if Terra (Earth is a dumb name, who want's to go around being called 'Earthlings', 'Terran's' sounds so much better) isn't being spun fast enough, you opt for a 425.

 

thanks guys for the input

 

as far as I know recent modifications have allowed provisions for raw petroleum gases to be pumped directly from under the Earth's surface into the intake manifold, negating the need for refueling. the only maintenance needed now, is the oil and coolant changes, but again provisions have been made to change these fluids much like a dialisis(sp) machine so that the motor shouldn't have to be shut down for another 100 million years.

John