I'm shocked that I never noticed this before… but new photos of the 4.5L Duramax reveal a change to Chevrolet’s V-8 architecture that hasn’t happened in 53 years: The 2010 4.5L Duramax engine bellhousing bolt-pattern has been changed.

For decades, every Chevy V-8 (with the possible exception of the Indycar engine program) has shared the same six-bolt transmission-to-engine bellhousing-pattern designed for the original 265ci small-block Chevy engine back in 1955.  

The upside to this commonality has meant that all Chevy V-8 engines; small blocks, big blocks, 90-degree 4.3L V-6 engines, 6.2L and 6.5L diesels, LT-1, LS1, 8.1L, and even the 6.6L Duramax will all bolt up to the same transmissions. This has helped make Chevy engines the most popular engine to swap into other vehicles.

The new Duramax 4.5L engine had to break from this tradition, presumably because the new diesel engine features a 72-degree cylinder block angle, which mandated a new bellhousing pattern.  That means enthusiasts won’t be bolt up able to bolt a TH400 or even an Allison 1000 transmission behind the 4.5L engine like they’ve been able to with other Chevy engines of the past-and that may be the only downside this engine has.