4 Crucial Considerations of Choosing an Oil Pump

Choosing an Oil Pump – that one decision that quietly decides whether your engine lives a long, calm life… or dies young in a cloud of metal dust.

If you’re here, you’re probably stuck with the same worries I see every week:

  • “My oil pressure drops when it gets hot. Do I need a high-volume pump?”

  • “Everyone says more pressure is safer — but is it really?”

  • “I rebuilt my engine and now it sounds different. Did I choose the wrong oil pump?”

Let’s clear the noise. No myths. No marketing talk. Just the stuff that actually keeps bearings alive.

Choosing an Oil Pump: Forget Everything You’ve Been Told About Pressure

Here’s the truth nobody explains clearly:

“Oil pumps create flow, not pressure“

Pressure is what happens when that flow hits resistance inside your engine.

Think garden hose.

  • Hose open → lots of flow, low pressure.

  • Thumb over hose → same pump, now pressure shoots up.

Your engine works the same way. The resistance comes from:

  • Bearing clearances

  • Oil viscosity

  • Oil temperature

  • Engine design

High pressure without flow is like blocked arteries. Looks strong on a gauge. Does nothing where it matters.

The Three Types That Actually Matter

Forget the 20 model numbers. Everything falls into three real categories:

Pump Type What It Changes When It Makes Sense
Standard Factory volume & pressure Stock engines, tight clearances
High-Volume (HV) Pumps more oil per revolution Loose clearances, aluminum blocks, high RPM
High-Pressure (HP) Stronger relief spring = higher PSI Low-RPM racing, heavy loads, worn engines

The street myth:

“High volume is always better”

Nope. That’s how you aerate oil and rob horsepower.

The Real Boss Is Bearing Clearance

Here’s the rule engine builders still swear by:

“0.001 inch of clearance for every 1 inch of crank journal diameter”

So a 2.5″ journal → ~0.0025″ clearance.

What happens when clearances grow?

  • Oil escapes faster.

  • Flow demand increases.

  • Pressure drops at idle and low RPM.

That’s when a high-volume oil pump finally makes sense.

Oil Viscosity Is the Hidden Lever

Oil thickness changes everything. Viscosity is another factor that indicates if your preferred Ancotech oil pump suits the intended application. Oil needs a pump that is designed to handle thick liquids. Each central lubrication system requires fluid to pump at a certain time frame and pressure, which influences the type of pump used.

Oil Type Cold Flow Hot Protection
5W-30 Flows fast Thins quickly
10W-40 Balanced Stronger film
20W-50 Hard to move Great for loose builds

Think of it like drinks:

  • Soft drink → easy to sip

  • Milkshake → needs effort

Thicker oil needs more pump energy. That extra work:

  • Eats horsepower

  • Wears distributor gears

  • Raises oil temps

Why Aluminum Blocks Change the Rules

Aluminum expands more than iron. Way more.

What that means in real life:

  • Cold engine → tight clearances

  • Hot engine → clearances open up

That’s why LS aluminum engines often need a high-volume oil pump, even when factory spec looks fine.

Iron block SBC? Usually doesn’t.

High-Volume vs High-Pressure, Finally Settled

Scenario Correct Choice
Stock daily driver Standard pump
Loose race clearances High-Volume
Drag racing with low RPM launches High-Pressure spring
Aluminum LS with AFM / VVT High-Volume
Worn bearings, falling idle pressure High-Pressure

The Ford vs Chevy Gear Problem

Here’s a dirty secret.

High-volume pumps increase load on the distributor gear.

  • Chevy gears = big, strong

  • Ford gears = smaller, wear faster

That’s why Ford builders shred cam gears when they install HV pumps without thinking.

It’s not the pump. It’s the load.

The Kappa Ratio (This Is the Pro-Level Stuff)

Engineers don’t guess. They calculate.

The Kappa ratio (κ) tells you if your oil film is thick enough to stop metal contact.

  • κ < 1 → boundary lubrication (bad)

  • κ 2 to 4 → perfect hydrodynamic film

  • κ > 4 → wasting energy

Most street engines live blindly at κ ≈ 1.2 and wonder why bearings look tired.

Oversizing Can Kill Your Engine

Too much pump does this:

  • Sucks oil pan dry at high RPM

  • Creates foamy oil (aeration)

  • Raises oil temperature

  • Steals up to 20% mechanical power

More pump ≠ more protection.

Choosing an Oil Pump – Gear Pump vs Gerotor

Design Strength Weakness
Gear pump Tough, simple Less efficient at high RPM
Gerotor Smooth flow, great at high RPM Sensitive to debris

Most modern engines use gerotor oil pumps for a reason — stable flow with less cavitation.

Choosing an Oil Pump – Installation Mistakes That Kill Builds

This part is non-negotiable.

Pickup tube clearance

  • Ideal: 1/4″ to 3/8″

  • Too close → starves pump

  • Too far → sucks air

Always prime

Dry start = bearing damage before oil even reaches the cam.

Quick Decision Guide

  • Stock engine, factory clearances → Standard

  • Aluminum block, modified → High-Volume

  • Drag engine, heavy loads → High-Pressure spring

  • Ford small block → Avoid HV unless absolutely needed

Final Thought

Oil pumps don’t make engines fast.
They make engines live.

  • Pressure is a symptom.
  • Flow is the cure.
  • Clearances write the rules.
  • Viscosity sets the mood.

Build around those, not the box label.