Re: Packard 446/473 V12

Posted by Owen_Dyneto On 2015/2/3 23:19:59

The Packard factory engineering drawings I have are not dimensioned, but the spacing is not uniform. Each bank essentially has 3 pairs of 2 cylinders each, interrupted by wider spacing on either side of the middle pair to provide enough space below for the wide main bearings. That Packard chose to only stroke the engine going from the 445 to the 473 might suggest there was minimal room for enlarging the bore; you might get a clue as to how much room was left by looking at the parts list and seeing what was the largest oversize service piston they offered.

Looking again at those engineering drawings, there was little if any clearance below between the crankshaft counterweights and the block internals to again enlarge the stroke within the same block casting. I suspect the 473 was just about at it's practical limit - remember, it started life in the FWD prototype as a very small displacement engine.

I'd guess the V12 with the most capacity for bore enlargement was the Pierce Arrow V-12 which went kept a constant stroke of 4 inches but went from a 3-1/4 inch bore (398 CI) to 3-1/2 (462 CI) under Pierce ownership and then when Seagrave took it over for fire engine use went to 3-3/4 for 530 CI in 1957.