We've covered oil pump types at a high level, but the pump's internal geometry and how it's driven determine everything about pressure delivery, parasitic drag, and how much horsepower you're feeding the oiling system at redline. Let's dig into the three dominant designs you'll encounter.

Gear pumps (external gear): Two meshing spur gears in a tight housing. Oil fills the gaps between teeth on the suction side, gets carried around the outside, and is squeezed out at the discharge. Brutally simple, tolerates contamination well, and produces high pressure. Classic small-block Chevy uses one driven off the distributor shaft. Downside: fixed displacement means at 7,000 RPM the pump is moving roughly 7x the oil it does at 1,000 RPM — most of which dumps straight through the relief valve as wasted work.

Gerotor pumps (internal gear/trochoid): An inner rotor with N lobes spins inside an outer rotor with N+1 lobes, offset on different axes. The expanding cavities draw oil in; contracting cavities push it out. Quieter than gear pumps, more compact, and usually mounted directly on the crankshaft snout — eliminating a drive shaft and reducing failure points. Nearly every modern OHC engine uses this. The Coyote 5.0, LS-series, and most German V6s all run crank-driven gerotors.

Variable displacement vane pumps: The game-changer for fuel economy. A rotor with sliding vanes spins inside an eccentric ring. By moving the ring closer to or further from the rotor's centerline, you change the swept volume per revolution. A solenoid controlled by the ECM commands low displacement at cruise (low oil demand) and full displacement when oil temp rises or RPM climbs. BMW's N20, GM's LT1, and the 2.0L EcoBoost all use these.

The parasitic loss reality: Rule of thumb — a fixed-displacement pump at redline consumes 3–5 horsepower on a typical V8. A variable pump cuts that to roughly 1–2 hp at cruise. Quick math: if your pump moves 10 gpm at 60 psi at 6000 RPM:

• Hydraulic power = (gpm × psi) / 1714 = (10 × 60) / 1714 ≈ 0.35 hp of useful work
• But pump efficiency is ~60%, so input shaft power ≈ 0.58 hp at that point
• Add relief-valve dumping and the real parasitic load at high RPM climbs to several hp

That's why GM's switch from gerotor to variable-vane on the LT1 (Gen V small-block) was worth ~2 mpg on the EPA cycle — free fuel economy with no combustion changes.