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Racing Technology
Hitting a gusher with a new wet-sump pump
by Wayne Scraba
It's no secret that racing in different categories can sometimes spawn serious mechanical dilemmas. The internal wet-sump oil-pump standard is something that, at first glance, looks like a catch-22: Race engines usually live longer with dry-sump systems, but regulations often prohibit running a dry sump (for a number of good reasons, not the least of which is cost).
The solution usually boils down to using a stock or modified factory-style pump; consequently, you're forced to live with all the factory-pump shortcomings: cavitation, pump chatter, scattered spark, broken pickup tubes, and so on. Band-Aid fixes exist for some of these problems, but some better ideas are available.
Titan Speed Engineering offers a series of dedicated race pumps with considerable improvements. Beginning with a clean slate, Titan re-engineered the internal wet-sump oil pump into a form that's more in line with the technology of a dry sump. It's not cheap, but neither are billet crankshafts, aftermarket rods, or dedicated race blocks. On the other hand, this wet-sump oil pump might be inexpensive insurance for anyone running high-dollar internal engine components in a category that mandates the use of an internal wet-sump oil pump.
Bench testing has shown that the Titan pumps flow 30 to 50 percent more volume than all other conventional wet-sump pumps. The pickup area is 80 to 90 percent larger, too, but, just as important, Titan's unique anticavitation design is arranged to prevent the destructive cavitation that affects conventional spur-gear oil pumps.
Pump basics
Before examining the differences between spur-gear pumps and gerotor pumps, I asked Bob Sanders of Titan to explain what goes on inside a conventional internal wet-sump oiling system.
Sanders said, "To pump oil in an engine, the first challenge is to get the oil into the pump. You have to understand that the oil begins to get contaminated by unburned fuel and combustion by-products as soon as the engine starts. Each contaminant lowers the lubricity of the oil, but, more important, the contaminants make the oil much more difficult to pump. Basically, pumping the oil means squeezing the oil (along with the new contaminants) up to something between 60 and 150 pounds per square inch of pressure.
"When the fluid fills the pumping chambers in both types of pumps (spur gear or gerotor), it must be at a lower pressure inside the chamber than outside of it. In order for the fluid to enter the pump, the higher, or more viscous, the oil is (a good example is cold SAE 60-weight oil), the harder it is to get the oil through the small holes in the oil-pump suction screen. As the oil becomes warmer, and more contaminated, it tends to be less viscous and will enter the pump with less drop in pressure. Also, the dissolved, or emulsified, fuel contamination becomes much closer to changing itself from a liquid state to a gaseous state. At this point, the fuel contaminants in the oil expand approximately 300 times. Remember that the pump is now pulling a vacuum reading on the oil, drawing it into the pump body. What the pump is pulling is a combination of oil and gaseous bubbles.
"This is where the two pumps differ. The gerotor configuration has four lobes on the drive, which take a little more than 180 degrees of crankshaft rotation to fill the pumping chamber. Meanwhile, the spur-gear design (using a 12-tooth gear configuration as an example) has only 60 degrees of crankshaft rotation to accomplish the same thing. Because the gerotor has more than three times the work time to fill its chamber, it allows the oil to accelerate smoothly into the pump chamber, then shut off slowly as it completes its cycle. This smooth action is less likely to pull gas out of the entering fluid than a spur-gear pump, which is trying to fill the chamber three times faster. (Liken this to shaking a soda can before you open it.) At 9,000 rpm, the spur-gear pump is trying to fill itself 54,000 times per minute; the gerotor is trying to fill itself at 18,000 times per minute."
Oil-pump cavitation
Pump cavitation isn't good. In fact, it can be destructive to both the engine and the pocketbook. Sanders explained what really happens when a pump cavitates: "Cavitation is always destructive, especially to objects that are near to it. Cavitation is what occurs when a gas is forced back into a liquid state. Basically, it's imploding bubbles. This causes the horsepower required to drive a pump to increase three to five times. Meanwhile, the oil coming out of the discharge of a pump drops to between 10 and 20 percent in volume. The total volume of the oil and the gas bubbles combined is often higher, which can make pressure measurement fool you.
"To compare how the two pumps discharge oil, you can see how the gerotor inherently is much less likely to cavitate. Again, the spur gear takes the same 60 degrees of crank rotation to hammer the oil and bubbles up to the selected bypass pressure. The gerotor design discharges three times slower and smoother through the 180-degree crank rotation. Significantly fewer bubbles implode if you squeeze them slower."
The one advantage to a very large pump that doesn't cavitate upon acceleration: This type of pump oils the bearings before the load is on them instead of after. Basically, both a spur-gear and gerotor pump put the same amount of oil into the lube system at a given pressure if there is no cavitation. Either configuration will only pump oil if there is oil in the pan.
Bypass surgery
Of the bypass circuit, Sanders said, "By design, the bypass in a spur gear must be discharged back to the pan. This translates into lost energy. If the bypass in a spur-gear pump was internal, this pump configuration would cavitate itself into destruction. On the other hand, the bypass system in a gerotor can be configured to pump into the upper-field (suction stage) kidney. This basically supercharges one end of the suction stage, which reduces the load on the pump drive, especially at high rpm."
So what's an aftermarket gerotor pump like in terms of construction? The Titan housings are CNC-machined from aircraft-quality 7075-T651 aluminum, then hard-anodized. Shafts are heat-treated, 300M tool steel. A special feature is an internal pressure-relief section. Each pump is bench tested before shipping. All models are infinitely adjustable and fully rebuildable. The press-in bearing is easily replaced; worn housings can simply be bored and fitted with new liners.
In most cases, the Titan pump fits inside the oil pan, bolting into the stock location. The built-in pickup assembly eliminates the inherent weakness of stock-type pickups, which can break off inside the pan. (Remember when Sanders mentioned the destructive forces of cavitation? That's what often breaks pickup tubes.)
Different Titan driveshafts adapt this pump to any late-model Chevy, Ford, and Chrysler small- or big-block V-8 or Donovan, KB, Fontana, Rodeck, or Arias engine. The correct driveshaft for your oil pump is included with the oil pump. Occasionally, stock-dimension small-block oil pans may require modification to accommodate pump length.
In the accompanying photos, notice how compact this pump design is and how it differs from a common spur-gear pump. Need to hit a gusher in the oiling system? That's what Titan's gerotor pump is all about.