The dry-sump oil pump is one of your race engine's MOST critical parts. It can be compared to the "heart" in a human body.
The pressure stage of the pump provides that vital supply of lifegiving oil to all the components and surfaces which require lubrication and cooling.
The scavenge stages of the pump serve two purposes, both of which are critical to best power production:
- removal of the "used" oil to minimize windage losses, and
- generating crankcase vacuum, which can provide a substantial power increase.
You might ask: "Why would I build a $40,000 race engine and not use a first-rate pump?" That’s a reasonable question, but it raises two more important ones:
- What defines a "first rate pump" ?
- Is the price of the pump necessarily an indicator of pump quality ?
Here is a list of the requirements of a high quality oil pump:
- It must deliver the required flow (gpm) of oil to the engine, throughout the temperature and RPM range, with enough pressure to assure the right amount of oil is delivered to parts which are most difficult to lubricate and cool (rod bearings, piston crowns, valve springs),
- It must effectively scavenge the outflow oil from the engine,
- It must generate a high level of crankcase vacuum for good ring seal and minimized windage losses,
- It must consume the absolute minimum power from the crank-shaft, and
- It must perform consistently and trouble-free for a long time.
The following sections present more detail on these requirements and explain how NRC pumps meet and exceed them.
RELIABILITY
Starting with requirement #5, in order to perform consistently and reliably, the pump must first attach to the engine rigidly and not wobble all over the place when the drive-belt loads fluctuate. NRC block-mount pumps use a specially-engineered double-mount-blade design (as shown in the picture above) which eliminates the wobble and flex found in single-blade designs. Of course, our NRC Cam-Mount and Bert-Brinn style mountings provide superior rigidity as well.
All NRC pumps use very high quality materials (AMS-4150 steel, 6061-T6 aluminum and a proprietary bronze), ball bearings, molded o-rings, along with precision manufacturing and assembly to assure consistent performance and long life.
PUMPING REQUIREMENTS
A good pressure pump, whether it is a gear-style, gerotor-style, or a lobe-style, delivers a relatively constant volume of oil for every revolution of the pump. The flow (Gallons Per Minute, or GPM) of oil delivered increases directly with pump RPM, almost without regard to delivery pressure. The delivery pressure is determined by the size of the effective orifice the pump is delivering oil to. That effective orifice is the combined size of all the holes for oil to flow through in the engine: rod, main and cam bearing clearances, lifter-body clearances, valvetrain restrictors, rocker-arm orifices, spring oilers, piston squirts, etc.
When the effective orifice gets larger, the pressure will decrease for the same delivered flow (GPM) and oil viscosity. For example, when the engine first starts, all the clearances are relatively small and the oil is cool, so the viscosity is high. That causes the oil pressure to be high at idle speed, and the idle oil pressure is usually determined by the bypass valve setting. After the engine reaches operating temperature, the clearances have increased significantly (especially in an aluminum-block engine) so, at idle, because the pump is turning slowly, the oil pressure at idle will be lower.
Conversely, when the delivered flow increases to a fixed effective orifice, the delivered pressure will increase. For example, when the engine RPM increases off idle, the pump flow increases, causing the delivered pressure to increase, until the pressure required to push the total pump flow through the effective orifice reaches the setting of the relief valve. At that point, the relief valve opens enough to maintain the pressure at that level. In order to maintain a constant oil pressure, the relief valve bypasses a portion of the pump output and routes it somewhere else (discussed further below).
These facts about oil pump operation and flow requirements generally cause the capacity of an engine pressure pump to be defined by the oil pressure requirements of the hot engine at idle. If the engine pressure pump has more capacity than that required to maintain suitable oil pressure at idle when the engine and the oil are both hot, it will waste power at any speed above idle.
For a complete discussion of how your engine bearings work and why they have amazingly-low frictional losses, read THIS ARTICLE
CRANKCASE VACUUM
In addition to a measurable reduction in windage losses, a dry sump pump that can establish a suitable level of crankcase vacuum can provide a substantial increase in engine power. There can be no argument that some of the high-end roots-style scavenge pumps do an excellent job of providing good scavenging and high vacuum levels. But our NRC gear-style scavenge sections, specifically optimized for high crankcase vacuum, have been demonstrated, both in side-by-side testing and in competition, to provide at least equal and often measurably superior vacuum levels. (See our expanded discussion of Crankcase Vacuum).
PUMPING EFFICIENCY
One of the most important aspects of high efficiency is the internal clearance between the gears and the housing elements. Tighter OD and side
clearance means less bypass leakage as the pressure increases. NRC pumps are manufactured on high-performance CNC equipment to provide very small
clearances in order to maximize pumping efficiency.
An often-ignored efficiency is the elimination of "root-trapping". These two pictures show how root trapping wastes power. The picture to the left shows one tooth of the bronze gear (turning counterclockwise) just entering the root cavity of the steel gear, and shows how large the root volume is at this point. The picture to the right shows how small that root volume becomes as the gears continue to rotate.
If that root volume of oil doesn’t have an escape path, the pump experiences a noticeable binding at every mesh, wasting power. NRC pumps have a clever root-trapping eliminator built into every stage.
Another important component of engine oil pump efficiency is the design of the bypass-relief valve system. Once the delivery pressure reaches the set point, the relief valve should maintain that pressure as RPM increases beyond that point. If the delivery pressure rises with RPM, the relief valve is poorly-designed and is causing you to waste power pumping oil. All NRC oil pumps have an optimized relief valve design to eliminate that power waste.
BYPASS OIL RECIRCULATION
Some pump manufacturers like to claim that recirculating the bypassed oil back to the inlet of the pressure pump causes the oil temperature to increase. Well, technically that is true. The problem is that the temperature increase due to recirculation is so small that it is difficult to measure accurately.
Those manufacturers who criticize recirculation claim their products are superior because, instead of recirculating the bypass oil back into the pressure pump inlet, they pump it back to the oil tank (or to the sump).
HOWEVER, sending the bypassed oil back to the tank (or the sump) creates an even bigger problem: The output of the pump at high RPM can be 30 GPM or more, while the engine requires only 8 - 12 GPM. That means that the pump will be bypassing at least 18 GPM through the relief valve to maintain the set oil pressure. If the bypass oil does not recirculate to the pump inlet, then the full pump volume (30 GPM or more) must flow from the tank to the pump inlet through the dash-12 inlet line, with only atmospheric pressure (at best) to move it. The reality is that it can't be done without reducing the inlet pressure below the vapor-pressure of the oil, causing pump cavitation, line collapse, aerated lube oil, and all the engine problems that follow those problems.
NRC pumps provide optimal pumping efficiency by recirculating the bypassed oil back to the inlet side of the pump.
GEAR PUMP ADVANTAGES
Several manufacturers claim that their gerotor-style pumps produce more "efficient" oil pressure with less "pulsing". Here, we have more marketing claims without any data to substantiate them. Depending on the style of gerotor pump, there can be just as many pressure pulses per pump revolution as produced by a gear pump. For example, the OEM gerotor-style pump which is in every wet-sump GM LS-series engine, has 9 lobes on the inner rotor. That produces the same number of pulses per pump revolution as a 9-tooth gear pump.
AND, it has been proven time and time again, in various forms of competition engines, that a gear-style pump is far more forgiving of debris than a gerotor pump. In our considerable engine-building experience, we have encountered far too many destroyed engines as a result of a jammed gerotor pump.
THE "OIL HEATER" PUMP
One of our competitors machines very pretty fins into the sides of their pump housings, then anodizes their pump bodies to a gorgeous black finish. He claims this helps to lower oil temperature.
WELL, just think about that for a minute. Where does a block-mounted pump live? Down at the bottom of the engine bay, right underneath a red-hot header. There is not much air circulation down there in a fendered race car, so the environment around the pump is very hot. In fact, it can be more than 150° HOTTER than your oil temperature! A black pump with FINS becomes a very effective OIL HEATER.
It is fundamental knowledge that heat flows from HIGHER temperatures to LOWER temperatures. Engineers have known for decades that black surfaces absorb the MOST radiated heat from their surroundings, while shiny, metallic surfaces absorb the LEAST amount of radiated heat from their surroundings. The NASA space people took maximum advantage of what is known as "black-body radiation properties" to provide the most efficient absorption and dissipation of heat (as the requirements dictated).
NRC pumps take maximum advantage of that science as well. NRC pumps all have a shiny, plain aluminum finish (and NO expensive, counterproductive fins) in order to absorb the very least amount of heat from the hotter surroundings, thereby reducing the load on the oil cooler.
BOTTOM LINE
From the facts presented here, you can see that the smart approach to sizing a pressure pump is to use the smallest pressure-stage capacity that will provide adequate oil pressure at hot idle. Whenever you are "on the relief valve", you are pumping more oil than the engine needs, wasting engine power.
NRC offers pumps in 1, 2, 3, 4 and 5 stages, with various options on pressure and scavenge stage capacities and on drive ratios, so you can optimize your pump selection to your engine oil flow and pan vacuum requirements.
The quality of the engineering and the manufacturing in a pump determines how well a pump meets the requirements described above. Any pump that meets those requirements, and at the same time costs substantially less than competitors’ pumps, must be a bargain first rate pump. NRC pumps are exactly that: first rate pumps at a much lower price.
