Quote Originally Posted by gromit View Post

It's interesting that the 6-cyl impeller is the same diameter, same number of blades but the blades are shorter. I did wonder if the flow was less than the 4-cylinder but it would depend on the speed it's run at.

As well as speed it will depend on the resistance to flow - which may well be quite different for the six. But I suspect that the reason for the difference is that like a lot of the engine, the pump for the four is over-engineered as it was originally designed as a diesel, and is also designed to be OK with stationary use. Remember that the four was designed for an offroad vehicle, where the six is a car engine.