Chevy engineers did a lot of things right with the Gen I small-block, but one of the engine’s most standout, yet underappreciated, design features is its oiling system. Although it was originally designed for a tiny 265-ci engine producing just 165 hp, with some very basic modifications, the small-block Chevy oiling system could easily support more than 600 hp. In an era when competing engine makes were plagued by oiling problems, this was quite an accomplishment. Building upon this foundation, the factory oiling systems in LS-series smallblocks are outstanding performers. With nothing more than a modified stock or aftermarket pump, the factory system is reliable past the 800-hp mark. The stock LS oiling system is so good, in fact, that there is very little engine builders can do to actually improve upon it.
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Unlike the Gen I small-block, the oil pump on Gen III/IV engines mounts to the front of the block and is driven directly off the crankshaft. The pump housing and drive gear slide over the crankshaft snout, and the pump gear is rotated by the crank keyway. By eliminating the camshaft-driven oil pump driveshaft used in the Gen I small-block, the Gen III/IV arrangement reduces drag placed on the valvetrain, as well as deflection and pumping losses.
The pump draws oil from the pan through a pickup tube, and after it’s pressurized, oil is sent down the main gallery on the driver side of the block en route to the oil filter. The oil then travels up the back of the block to the main feed gallery, which runs through the lifter bores. From there, oil trickles down to the main bearings. Just like the Gen I small-block, LS-series engines direct oil to the cylinder heads through holes drilled into the lifters and pushrods. This lubricates and cools the valvesprings and rocker arms, and the oil then drains back into the pan through passages in the cylinder heads and block.
Oil is the only thing preventing the moving parts in an engine from seizing up. Before delving deeper into the specifics of the LS-series oiling system, it’s important to investigate the very basic principles of lubrication, which can be divided into three different states. Hydrodynamic lubrication describes the ideal situation where a continuous film of fluid separates two sliding surfaces. During hydrodynamic lubrication, the viscosity of the oil supports the entire load between moving parts and prevents them from touching.
The extreme opposite end of the spectrum is boundary lubrication, which is the last line of defense before metal-tometal contact occurs. When oil is squeezed out from between moving parts in high-load areas, such as the main journals and bearings, all that’s left to prevent excessive wear are the anti-wear additives in the oil.
Mixed film lubrication is a little bit of both, where some oil has been squeezed out, but a thin coat of oil is still present.
Each state of oil is present somewhere in the engine, which makes formulating oil very complicated. Ideally, hydrodynamic lubrication would be achieved under all conditions, but because this isn’t possible, it makes the oil much more important.
Pressure vs. Volume
Oil control is a balance between pressure and volume, and although cars come equipped with pressure gauges, there’s no way for the average hot rodder to measure the volume of oil that’s flowing through an engine. In essence, oil pressure is used as an indirect method of measuring oil volume. As oil is pressurized in the pump, the resistance against the pump outlet creates oil pressure. Elementary physics dictates that pressure must be present in order to move oil through an engine, so in this regard, pressure is a good thing. However, excessive pressure merely increases an engine’s pumping losses and adversely affects power output. Because pressure demands increase with RPM, it’s generally recommended that an oil pump should be able to supply 10 psi of pressure for every 1,000 rpm. In other words, an engine turning 6,500 rpm needs roughly 65 psi of pressure for proper lubrication.
Even so, as long as sufficient volume is present to fill the clearances between moving components and remove heat from the bearings and journals, oil pressure is somewhat irrelevant. This is important to remember in performance engine builds that typically employ looser bearing clearances than stock engines. As clearances increase, a greater volume of oil is needed to maintain a target oil pressure. High-volume oil pumps help increase pressure to the desired level, but they aren’t always necessary. It’s quite possible that a stock pump can supply plenty of volume and pressure in a typical stroker buildup. Furthermore, oil pressure is also affected by oil viscosity and temperature. Thicker oils, and colder oil temperatures, increase oil pressure, but not volume. This merely reinforces the point that although having sufficient oil pressure is important, having proper oil volume is an even greater priority.
Sticking with the philosophy of not fixing things that aren’t broken, there are only three basic types of oil pumps used by GM throughout the entire LS engine lineup. All Gen III/IV smallblocks use identical oil pumps, except for displacement-on-demand engines, which use higher-volume pumps. Consequently, there is no advantage to taking an oil pump off an LS6 and installing it onto an LS1, or using an LS3 pump on a 6.0L truck motor. The one major deviation within the LS family is the LS7 pump, which is completely different, because it’s designed to feed a dry sump system. The LS7 unit is actually two pumps in one, as it moves pressurized oil like a conventional pump, and it also scavenges air and oil out of a dry sump pan. As a result, the LS7 pump isn’t compatible with any other LS-series smallblock, unless a motor has been converted to the factory dry sump system.
Aftermarket oil pumps are available from Melling and GM Performance Parts. These units are offered in both standardvolume and high-volume configurations. For engines with loose bearing clearances, these aftermarket pumps can increase oil volume by 10 to 33 percent. That said, a standard-volume pump typically supplies enough oil for the average stroker small-block. Companies, such as Lingenfelter Performance Engineering and SLP, also offer pumps, which are slightly modified versions of the aftermarket or stock replacement oil pumps. Many engine builders opt to port the inlet and outlet passages of the oil pump. This process involves radiusing the inlet and outlet passages of the pump to create a smooth transition point between the block and oil pump pickup. In theory, this is said to improve oil flow volume, but in practice, it has a negligible impact on pump performance.
The Gen III/IV oil pan is a unique design in that it serves as a structural member of the engine. This enhances block stiffness and helps reduce vibration. Throughout the LS-series production run, GM has used several different types of oil pans, primarily to account for the installation needs of various types of vehicles. Early LS-series small-blocks featured three basic oil pan designs. They included the F-body pan used on fourthgen Camaros and Firebirds, the “batwing” oil pan used on C5 Corvettes, and the deep sump oil pan used on trucks and SUVs. As with intake manifolds, each of these pans was designed more for fitment within the chassis than achievement of certain performance benchmarks. Still, each of them offers excellent oil control, and as a testament to the seriousness with which GM approaches oil control, each style pan incorporates a windage tray.
Because its sump location allows the best fitment into a wide variety of chassis, the F-body oil pan is the most popular choice for engine swappers. In contrast, the truck pan’s extremely deep sump doesn’t provide adequate ground clearance in most street machines, so it isn’t a very practical option for anything other than a truck. Due to the Corvette’s very low ride height, engineers had to get creative by kicking the oil pan sump out to the sides to ensure adequate oil capacity and ground clearance. This also means that the Corvette pan provides excellent oil control under high cornering loads, but its unique shape makes it difficult to install into most chassis.
As GM installed the LS-series smallblock into more cars, it produced several variations of its three early oil pan designs. The LS2 Corvette oil pan did away with the C5 pan’s batwing design, and it features a long 13.5-inch sump section that makes it difficult to fit into most cars. Likewise, the oil pan used on the Cadillac CTS-V features a sump design deeper than the F-body pan but shallower than the truck pan. Even so, it offers inadequate ground clearance for many engine swap applications. The same applies to the LH8 oil pan used on 5.3L-powered Hummer H3s. It has a long sump section that clears most crossmembers, but its deep 7.5-inch sump makes it difficult to install.
Because extensive research and development (R&D) efforts went into designing factory GM oil pans to make sure they performed well under both longitudinal and lateral loads, and had rugged cast-aluminum construction, the most compelling reason to use an aftermarket oil pan is for improved chassis fitment. Aftermarket pans are typically constructed from aluminum sheet metal, which gives engineers more flexibility in designing a pan because they don’t have to invest in the tooling required to build a cast pan. The number of aftermarket oil pans for the LS platform is staggering, and each is designed to fit in a specific chassis. Although it isn’t feasible to list all of the available aftermarket oil pans here, most pans generally offer a similar list of benefits.
Many aftermarket pans are built with the average street cruiser in mind, but companies also offer specialized designs for drag racing and road racing applications. Because drag racing oil pans only need to perform optimally during straight-line acceleration and braking, they tend to have much deeper sump designs. In contrast, road race pans have kicked-out sumps for improved ground clearance. Furthermore, drag racing pans usually have a single trap-door baffle that prevents oil slosh and helps keep the pump pickup submerged during acceleration and braking. Trap doors function by trapping a pocket of oil under normal driving, and then swinging open under high g loads to release a pocket of oil to keep the pickup submerged in oil. Road racing pans take this concept one step further by employing several trap-door baffles for superior oil control under cornering loads.
Dry Sump Systems
Once considered the exclusive territory of full-blown race cars, enthusiasts were in disbelief when GM revealed that the LS7 would feature a dry sump oiling system. Even though dry sump systems have found their way into high-end street cars, they’re still rather exotic by nature. As their name implies, dry sump oiling systems don’t use a conventional oil pan. Instead, oil is stored in an auxiliary tank mounted elsewhere in the chassis, and the oil pan merely functions as a collection bin that catches oil dripping off the crank, rods, and block. A crankdriven pump scavenges this oil, and then circulates it into the storage tank before making its way back into the block.
Although complicated, this arrangement offers several benefits. For one, having no oil in the pan eliminates windage and frees up horsepower. This reduction in windage is why many drag race engines that turn 8,000-plus rpm utilize dry sump oiling systems. Second, storing the oil in an auxiliary tank takes oil slosh completely out of the equation, ensuring an uninterrupted supply of oil to an engine’s critical parts under even the highest of cornering loads. Additionally, the low-profile design of a dry sump pan allows mounting an engine extremely low in the chassis for improved handling. That said, only a very small fraction of LS builds require a dry sump oiling system. If deemed necessary in an autocross or road racing application, the stock LS7 system can be retrofitted into just about any chassis very easily. Furthermore, several aftermarket companies offer dry sump conversion systems.
An oil’s ability to properly lubricate moving parts is dependent upon its operating temperature. For every 18- degree increase in oil temp, the oxidation rate doubles. That means that although the difference between 200- and 220-degree oil temps might not seem like a big deal, every last degree of temperature increase has a dramatic effect on oil performance. Consequently, it’s not surprising that GM installed a factory oil cooler on just about every Gen III/IV small-block ever built. Latemodel engines typically operate at higher coolant temperatures than older engines in an effort to reduce emissions output, which explains why factory oil coolers are so common. Although they’re not mandatory on stroker smallblocks, which are typically set to operate at lower coolant temperatures, they’re cheap insurance and help extend oil longevity and performance. Stock oil coolers are usually integrated into a car’s cooling system, so in engine swap applications, it’s easiest to install an oil cooler offered by several aftermarket manufacturers, such as TCI and B&M.
Installing an oil temperature gauge is an easy way to keep an eye on how much heat is in the oil. Under steady state cruising, where a constant supply of air is moving through the radiator and oil cooler, oil temps generally mirror coolant temps. In stop-and-go traffic and heavy acceleration, however, oil temperature usually gets much higher than coolant temperature. Without a gauge, trying to figure out oil temp is just a guessing game.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks
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