Lubrication: Picking the Right Wet Sump Pump

Drag Race 101: Lubrications, Picking the Right Wet Sump Pump

Here’s the ideal scenario for choosing a wet sump pump for your lubrication needs:  So, you’ve built an engine for your strip burner that tops out at around 500 horses and you’ve chosen wet sump oiling. You’re not expecting lots of G’s when you launch. You’re also not going to be popping wheelies. Plus, you don’t want to spend few thousand dollars for a dry sump system. That engine is a perfect candidate for wet sump oiling.  Let’s take a look at the types of pumps out there that’ll keep you within your budget while still providing ample lubrication for your engine.

It’s true that when we race our cars at the drag strip and not on the street or a track we don’t run them for very long. However, our engines aren’t little putt-putters that put out a hundred or two hundred horses, max; they put out a minimum of 400 to 500 horses, hopefully. That increase in horsepower comes with an attendant increase in heat generation-more power = more heat.

There’s also the fact that we shut our engines down between passes, causing them to heat up more quickly, and then abusing them so badly during our passes, the oil has to work doubly hard at start-up.

It’s true that all of these pumps will deliver an increase in both volume and pressure, both of which we need to protect our engines. However, too much pressure can blow seals and gaskets, while not enough pressure can also cause leaks. Your econo-box daily driver has a max operating pressure of 40-60 PSI. This is what a standard volume-standard pressure pump would deliver. For a somewhat quick-fix and low-cost fix, as an engine’s bearings wear you can install a standard pressure-high volume pump. This increases the volume and keeps the film of oil that the bearings ride on constant.

The cars we build for the dragstrip might turn 10,000 RPM, though. The faster the engine rotates, the faster the oil is sprayed out from the bearings, lowering the pressure. This engine is the engine that will need a pump that can deliver up to 100 PSI or a little more.  You’re looking for a happy medium, with lube system pressures reaching about 60-70 PSI at max RPM.

When to Pick a High Volume Wet Sump Oil Pump

In my years of working on cars and building race cars, I’ve never really uncovered a hard and fast rule for this decision. I’ve had old car guys that I respect immensely tell me conflicting stories over the last 40 years or so. Here’s what I’ve been able to distill out of all that:

• If you’re not going with an external oil cooler, you want a high pressure pump. This keeps good lubrication flowing at high RPM through the bearings and properly lubes the rockers/lifters/etc.
• If you are going with an external oil cooler, in order to maintain proper pressure and volume, you want a high pressure-high volume pump. The tubing involved expands, causing pressure drops, plus the pump needs to move more oil.
• If you’re building an engine with hydraulic lifters, such as a Mopar engine, you need both high pressure and high volume in order to keep the lifters pumped up. This is especially important if you’re going with the external oil cooler.

Choosing Oil Pump Pressure

Determining whether or not you need a high pressure oil pump depends on two things. The first is something I learned when I was first learning how to build engines. You need ten PSI of pressure for every 1000 RPM. This means if you expect to run your engine up to 8000 RPM, you need a pump that can deliver 80 PSI.

Bearing clearance is another major factor in choosing between a regular and high pressure pump. If you’re going to run your engine with a slightly larger bearing clearance, you’re going to need a higher pressure pump. Larger clearances allow for more oil to escape which lowers pressure.

Choosing the Right Pump for a Few Hypothetical Engines

Let’s take a hypothetical big block Chevy engine that has close tolerance bearings and will turn a maximum of 8000 RPM. The engine will have an oversize filter on an external mount and a large external oil cooler. The stated engine RPM of 8000 means that we’re going to need a pump that can deliver a relatively high pressure-80 PSI, so we need a high pressure pump.

However, the external cooler and large external filter increase that demand. Because of the increased volume of oil that has to be moved, it needs a high volume pump. This engine needs a high pressure-high volume pump.

If the engine described above is only equipped with an external filter, the pump specs can be decreased to high pressure-standard volume. If you expect your shift points to be no higher than 6000 RPM, you would only need a standard pressure and volume pump.

Oil pumps are equipped with a pressure relief valve. When I’m building a new racing engine I take advantage of the fact that there are makers of high performance oil pumps that are adjustable. This makes it so that I can run tests in the shop with the engine on the dyno and adjust the pump to deliver the optimal maximum output pressure. The adjustment is usually made by turning an Allen (hex) key.

A Word on Monitoring Your Lubrication System

I’ve got to put in a word here on monitoring your engine’s lubrication system. This doesn’t mean to simply check the level and condition between passes. It means keeping an eye on the vitals while the engine is running to head off BIG problems. This means you need an oil pressure gauge that is accurate. It also means you need an oil temperature gauge that is accurate.

NOTE: A water temperature gauge is not the same as an oil temperature gauge. Water is much thinner than oil and transfer heat more readily. I can’t go into the electrical and physical differences here, but they are significant enough that any temperature reading using a water temp gauge and sending unit will not generate accurate readings. The correct gauge is a little more expensive, but well worth it in the long run.