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Is the block the same for 326 as the 400 V8? I read on Pontiac Enthusiast site that "The Pontiac 350 is neither a big block nor a small block, it is a Pontiac V8. Other manufacturers had both small and big block motors, most notably Chevy, but Olds and Buick both had small or at least smaller block versions of their motors. Pontiac used one basic size block for everything, with the exception of the later 265 and 301 low deck motors that everyone wants to forget. "

Will parts from 326 engine interchange on 400?
 

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67 Basket Case Restorer
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2,717 Posts
The pistons and crank won't but everything else will.
 

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64-67 Expert
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Olds motors are like Pontiacs....a 260 is the same size as the 455. Buicks likewise: a 350 and 455 are indistinguishable. Chevy, Ford, and Mopar had the "small-block-big-block" thing going....Pontiacs are all big-ish blocks, weighing what they do. They're certainly closer to a big block than a small block. Pontiacs DID differentiate between Small Journal And Big Journal motors....the 326-389-400 v8's had 3 inch main journals on the crank, whereas the 421-428-455 had 3.25 inch mains. As mentioned above, the parts will interchange. The most common performance block used is still the 400. It's more readily available than a 389, is of good size and power, and is affordable to build up. My favorite Pontiac engine is the 421. I've never owned one!
 
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