Hi,
I took this from another site, as you can see, the H4 (left) has a longer rotor, thus moving more oil per turn
( http://forums.hybridz.org/showthread.php?t=150165 )
the spring I'm referring to is the one in the relief valve, I believe some have a higher pressure spring, thus making the pump , pump at a higher pressure,
I need to look at what pump I have to see what numbers are on it, but when I brought it 4 - 5 years ago, it was for a L24,
Nigel