It\u2019s true that when we race our cars at the drag strip and not on the street or a track we don\u2019t run them for very long. However, our engines aren\u2019t 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.<\/p>\n
There\u2019s 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.<\/p>\n
![\"Sealed](\"http:\/\/www.racingjunk.com\/news\/wp-content\/uploads\/2014\/12\/slp-224-43364s.jpg\")
<\/a><\/p>\n
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- a standard volume-high pressure oil pump<\/li>\n
- a high volume-standard pressure pump, or<\/li>\n
- a high volume-high pressure pump<\/li>\n<\/ul>\n
These categories can be misleading because science tells us that if you increase the volume of flow without increasing the size of the conduit, pressure automatically increases, while if you increase pressure in the same type of system, volume automatically increases.<\/p>\n<\/div>\n
It\u2019s 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.\u00a0Your 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\u2019s 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.<\/p>\n
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. \u00a0You\u2019re looking for a happy medium, with lube system pressures reaching about 60-70 PSI at max RPM.<\/p>\n
![\"Milodon](\"http:\/\/www.racingjunk.com\/news\/wp-content\/uploads\/2014\/12\/MIL-18800_GN.jpg\")
<\/a>Milodon High Volume-High Pressure Oil Pump<\/figcaption><\/figure>\n <\/div>\nWhen to Pick a High Volume Wet Sump Oil Pump<\/strong><\/p>\n
In my years of working on cars and building race cars, I\u2019ve never really uncovered a hard and fast rule for this decision. I\u2019ve had old car guys that I respect immensely tell me conflicting stories over the last 40 years or so. Here\u2019s what I\u2019ve been able to distill out of all that:<\/p>\n
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- If you\u2019re\u00a0not<\/em>\u00a0going 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.<\/li>\n
- If you\u00a0are<\/em>\u00a0going 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.<\/li>\n
- If you\u2019re 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\u2019re going with the external oil cooler.<\/li>\n<\/ul>\n
Choosing Oil Pump Pressure<\/b><\/p>\n
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.<\/p>\n
Bearing clearance is another major factor in choosing between a regular and high pressure pump. If you\u2019re going to run your engine with a slightly larger bearing clearance, you\u2019re going to need a higher pressure pump. Larger clearances allow for more oil to escape which lowers pressure.<\/p>\n
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Choosing the Right Pump for a Few Hypothetical Engines<\/b><\/p>\n
Let\u2019s 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\u2019re going to need a pump that can deliver a relatively high pressure-80 PSI, so we need a high pressure pump.<\/p>\n
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.<\/p>\n
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.<\/p>\n
Oil pumps are equipped with a pressure relief valve. When I\u2019m building a new racing engine I take advantage of the fact that there are makers of high performance oil pumps that are adjustable<\/a>. 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.<\/p>\n
- If you\u00a0are<\/em>\u00a0going 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.<\/li>\n
- If you\u2019re\u00a0not<\/em>\u00a0going 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.<\/li>\n