Hi Ed,
The 2L pumps use straight cut gear sets, designed to carry more oil volume at lower engine speeds. They also feature a stepped (3 size) main shaft bottom end for machine hydraulic assembly rather than hydraulic assembly gauged by hand. While a decent performance pump can be built from a 2L straight cut gear pump, it may be more time consuming and have a shorter service life than a pump built from a 9 tooth helical pump core.
Here is what happens. With the straight cut gear set, both gears have the same size gear bore to be interchangeable. Not so with helical pumps, where the idler gear has a larger bore. To get the same O.D. tooth size to carry more volume with straight cut (SC), the gears have longer teeth, and a smaller hub. The first photo below shows a drive gear with a fracture at the gear tooth root from a gear loading failure at 7500 rpm. This partly due to the smaller gear bore (less material) partly a stress fracture from machining stress risers, and the pressure of the interference fit on the main shaft. Next pictures are the stepped main shaft on the (SC) pump. Following pictures show that the shaft tip galled in the pump bottom bush, wearing the bush oval and allowing the bottom of the drive gear to move to -0- radial clearance with shaft flex, chewing into the gear bore. This caused the shaft to first twist (red mark) then snap off at the through pin on the drive gear. All this happens as oil trapped between gear teeth at high rpm cannot escape quickly enough, causing excessive gear loading as both gears try to move away from one another. While this is happening, the smaller diameter idler pin in the SC gear pump tilts away from the drive gear and main shaft, reducing the upper radial clearance to -0- as that gear cuts into the gear bore. Examine some dead SC pumps for confirmation.
The helical pumps (H) use a larger diameter idler pin, with better support in the pump bottom. Main shaft is single diameter, full length, so loading on the shaft tip in the pump bottom boss is reduced. Shaft flex is also reduced as the full diameter shaft is stiffer than the stepped shaft. Finally the helical gears do not push directly away from one another as much, with oil trapped between teeth, at high rpm. The 9 teeth will carry less oil volume than the same OD 9 tooth SC gear, but handle higher speeds better, without damage. Experimentally, we ran a race, double steel helical geared pump at 6,000 rpm for about 2 minutes. This is 12,000 rpm engine speed. We stood FAR away. It did get warm, not hot. Disassembled, there was no measurable clearance changes from the initial build. I will not repeat this test, as it was a bit frightening.
All this aside, the QUALITY 2L pumps are perfect for intended (FI engine) use. The standard 31 mm gear version works just fine with 20-50 mineral base oil, the "tall-gear" version was designed for use with much lighter weight oil or synthetic, and is also fine used as designed. Both these pumps were intended for ~5500 rpm maximum engine speeds. Higher speeds cause earlier pump failures.