bigblock pontiac? i dont think so.

[titleist312]

does anyone else agree with me that other than sounding "cool" there really is no such thing as a bigblock pontiac and if you disagree can you please tell me "oh wise one" the external size difference between a 301,350,400,or 455. the average joe would never no the difference by looking at them. It irritates me when someone is selling their car on ebay and advertise that it has a 400 or 455 bigblock.

[paul1965]

While I'm really not a fan of GM products (sorry, I've got blue oval blood!), I did run across this on the web:
Remember, Pontiac never made a "small-" or "big-" block--they used the same block dimensions from the small 326 all the way up to the 455. This "mid-block" design was a stout one--as was proven over and over again on the streets of America throughout the '60s and '70s. The Pontiac design served as the basis for the small-block Chevy (note the port configuration and stud-mounted rockers), and like its GM cousin, possessed tremendous potential. Only a few modifications must be addressed to make the bigger-inch (400-plus-cube) Pontiac V-8 a real street contender, and enthusiasts have always gravitated toward the larger-displacement engines.

From what I can know, this only applies to Pontiac. I know from personal experience, that Ford, Chevy and Dodge all made small and big blocks. And yes, there is a major physical difference between them (try swapping a Ford 429 in between the shock towers of a factory 289 equipped 68 Mustang!).

[sonhasteg]

I know this is old, but I had to reply just in case someone else read it...

Although you are correct that the blocks are physically the same size, there are differences in the internal castings. The 301 was a different animal and I don't know much about it.

The 326 & 350 were the small bore blocks. I don't know what the 326 bore was, but the 350 was 3.88 - considering they shared the same 3.75 stroke it must have been a little smaller.

The 389 & 421 were the big bore blocks (4.06 & 4.09 respectively). Although the 389 shared the 3.75 stroke you couldn't bore a 350 .18 over (.030 if you were lucky) to make a 389. It was the block that made the 4.06 and 4.09 bore possible. The 421 had a 4.00 stroke crank.

Pontiac made a slightly thicker cast block to make the 400 & 428. The thicker casting allowed a 4.12 bore. 3.75 stroke for the 400 & 4.00 stroke for the 428. The main journals were also increased in size (I don't recall the sizes), so the older 389/421 cranks won't drop in. Since these took the place of the 389 & 421, these became the big blocks.

Another thicker cast block produced the 455. A 4.14 bore and 4.21 stroke crank. It replaced the 428 and by this time the 326 was discontinued. The 350 was the lone "small block" and the 400 & 455 were the "big blocks."

Sadly, those also were eventually dumped for the corporate motors.

Didn't the '68 'Stang have an 428 CJ option? Also, isn't the 351 physically larger in size to the 289/302, but smaller than the big blocks? The 351s are still considered small blocks.