Short- and long-impeller water pumps

[Sarastro]

I've noticed that there are two types of water pumps for spridgets: a short-impeller pump, used from the beginning up to some point in the 1275 production, and a long-impeller pump afterwards. Anyone know if the difference is significant? Specifically, can you get away with the short-impeller pump on the later 1275s? I have a hard time seeing why later 1275s might need more cooling, but perhaps they do.

Moss lists two different pumps, but, interestingly, VB lists the same replacement pump for all engines. That implies that there isn't much difference.

 

[spritenut]

short impeller pumps are needed for the thin flange 12CC block (1967)
All later 1275s from 12CD on can use the deeper impeller.
Since I have a couple of each of these blocks on various 1275 powered cars, I always order the shallow pump for my spares shelf and it works fine on either block.

 

[Sarastro]

Thanks. I thought something like that might be the explanation.