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Lubrication

 - Protects and cools engine components.
 - Seals the piston rings to the cylinder.
 - Cleans the engine and minimizes chamber deposits.


The basic function of any lubrication system is to protect vital engine components by preventing metal to metal contact and premature wear or seizure.

The lubrication system of modern engines performs a host of other related functions. It cools the bearings, pistons and valve springs. It is literally squirted onto these and other components to transfer the heat from the components to the oil.

The oil must also provide a seal between the piston rings and the cylinder. It must allow easy starting when the engine is cold, keep the engine clean and minimize combustion chamber deposits; it must be Lambda probe friendly and CAT friendly. It must also provide good corrosion protection and resist foaming.

While doing this the lubrication system must be designed so that the oil doesn’t spend time in areas of the engine where it will impede performance. Increased parasitic losses can occur which will lead to less power and less fuel economy. Also, if oil is overexposed to fast moving parts such as the crank, it can be badly foamed up and make it difficult to pump and reduce its cooling effects.

Oil Test Standards.
 - Standardized tests exist to rate oil based on its performance under various conditions.

To indicate an oils performance in the areas mentioned, the oil makers carry out tests and print the results on the oil bottle. The API assigns oil a service rating starting at SD and ending at the toughest rating SL. To carry that rating the oil must pass a series of tests carried out on an engine dyno. These tests include testing for valve train wear on a 2.3 Ford engine (which is notorious for valve train wear). Another test runs a 4.0 engine at full load for 64hrs with the oil at 149degC. Poor quality oils end up as sludge and high quality oils easily last through this test (usually fully synthetic). Some oils are so good that they last for 128 hours and beyond. There are the oils we are interested in. Some oils may be outstanding in some areas and average in others, while other oils are generally good in all areas. These are the oils to use.

Viscosity and Horsepower.
 - Good all round protection should be considered before absolute horsepower.

A good all-rounder for forced induction and NA engines would be a 5W-50 grade viscosity. It will give good all round protection without overly cutting down on horsepower. For maximum horsepower a viscosity of 0W-40 grade can be used but it won’t afford the same protection. But with controlled warm-up of the engine and with more frequent oil changes it is fine and is the only real choice for competition.

Friction Modifiers.
But viscosity isn’t the last word in horsepower. A higher viscosity oil with better friction modifiers will give more horsepower than a lower viscosity oil with poorer friction modifiers added. On a Subaru 2.0L turbo, the following figures were noted…

RPM Mobil 1 Mobil1 Shell Castrol R Castrol SLX
  5W-50 0W-40 5W-40 10W-60 0W-30
3000 143.2 142.9 144.8 140.5 138.6
4000 202.9 202.4 201.3 203.6 201.2
5000 263.1 266.6 262.5 262.4 260.8
6200 304.3 311.2 303.5 306.5 305.1

Viscosity and Viscosity Improvers.
 - High viscosity may be too thick to flow between modern engine components.
 - Low viscosity may be too thin to provide a protective layer.
 - A middle ground must be chosen which gives maximum protection.
 - Oils with a high viscosity index are desirable so long as this index hasn’t been achieved
    through the use of polymers.

The viscosity of an oil relates to the oils ability to flow through a graduated hole as a specific test temperature. The winter rating (W) is carried out at -18degC and the summer rating is carried out at 100degC for the SAE rating. Higher viscosity oils leave a thicker film than lower viscosity oils. If an oil is too low(20 or less) it wont be thick enough to provide a layer that keeps moving parts from direct contact such as gears and rings to chambers. If it is too high in viscosity (60 or more) then it is so thick that it wont get in between tightly fitting parts sufficiently to conduct heat away.

Temperatures build up because of this and because these oils trap heat rather than dissipating it. They also trap air, so de-aeration is a problem. All oils become thinner when they heat up and thicker when they cool down. An oil that gets very thick when it cools down will also get very thin when it is very hot. Other oils better maintain their viscosity at low and high temps. They show a minimal viscosity change from the max to min temperature range. These oils are classified as having a high viscosity index.

The more variable viscosity oils have a low viscosity index. Obviously, an oil with a high VI is desirable provided that this high VI rating hasn’t been achieved by using additives. VI improvers (polymers) thicken the oil as it heats and thin it as it cools, thus maintaining a high VI rating. These polymers are improving but they are not shear-stable at high loads. They tend to momentarily lose cohesion during high stress operations. This is most likely to occur at critical points such as the bearings and tappets. This is why you have to run in an engine using straight 30 or 40 grade oil.

Synthetic Oils.
 - The only option for high performance engines.
 - High viscosity index without using polymers.
 - Only use oils that are blended to fully synthetic
 - Don’t use oils that reach their fully synthetic attributes through using additives.

There is a better route available to achieve a high VI. Blending synthetic base stock with mineral oil base stock to produce a blended synthetic also gives good VI. Such oils contain mineral oil, synthetic and polymers to produce a high-grade, wide-viscosity oil suitable for road use.

Taking this a step further produces fully synthetic oils. In reality they are not 100% fully synthetic because a good portion of the base stock is mixed with additives. However, if the base stock is fully synthetic then it truly is a fully synthetic oil. Such oils don’t contain any polymer improvers, and the high VI is achieved by special refining techniques. So to recap, semi-synthetic oil is good for normal road use and is better than the oil mineral oils… but better still are the fully synthetic oils. There are two types of fully synthetic.

The cheap and lesser quality type with additives and the more expensive 100% fully synthetic types that are refined to produce their high quality attributes. Mineral oils are produced from petroleum crude oil after the distillation process has removed most substances like tar, petrol, diesel, kerosene etc. Synthetics go further in the refining process until the very basic components in the crude are separated. These base components are then combined into molecular structures to produce synthetic base fluid. Some synthetics are derived from petroleum crude only, while others are derived from coal, natural gas, animal fat, bone marrow etc…

Synthetics provide benefits to performance engines over the best mineral oils. They lubricate better when cold and don’t overly thin out at high temps. They are more oxidant-resistant so are less stressed by high operating temps.

Oil Additives.
 - Some additives are essential to an oils performance.
 

Besides polymers, oil contains other components. They work as anti-oxidants, some as detergents, some as foam suppressors and others as anti-wear additives. They can make up 20% of the oil volume. Oxidation occurs because of the oxygen and combustion by-products in the oil. As the oil temps rise past 100degC the rate of oxidation increases and the anti-oxidant becomes less effective. The byproduct is sludge. Detergent is used to keep this sludge in suspension and not allow a build-up inside the engine. A foam suppressant is used to counter aeration. But it cannot eliminate the foam caused by water in the oil or from air sucked in through cracks or due to oil surge. The oil must be changed before these additives are depleted.

Oil Changes.
 - Change every 3000miles for stop/start driving.
 - Change every 8000miles for long haul driving.
 - For most performance cars, change the oil every 5000miles.
 - Change the filter every 10000miles or sooner if worried about swarf.

The air temp and driving conditions determine how often the oil should be changed. Stop- start driving and temps below 10degC are hardest on oil. Long distance driving with little idling in warm weather is easiest on oil. Fully synthetic oil should be changes every 3000mls under the first condition and every 8000mls under the second condition (with the filters changed at the mid points). For rally engines you should change the oil after every event or as much as your budget will allow. Its better to use good oil for two events rather than use poorer fully synthetic and changing it after each event. But less oil changes can be carried out if you’re not worried about metal swarf or about very rich mixtures thinning out the oil. If mixtures are very rich, then draining the oil and gently heating it to 100degC can evaporate off any contamination by fuel or oil.

Oil Temperatures and Oil Coolers.
 - An oil cooler is used to supplement the coolant system.
 - It is not necessary to use an oil cooler is your main coolant system is adequate.



Oil must be kept at the right temperature to operate correctly. A lot on engine wear occurs at warm up when using cold oil and water. The oil should be at 70degC before driving the car at full load. The ideal operating temperature is 95degC but can go as high as 130degC for short periods. Above this temp. oil will breakdown. In a rally engine, horsepower is lost above 110degC and bearings will fail above 130degC. Oil coolers are used to control the oil temperature and to take heat out of the engine when changes to the coolant system is impractical or overly expensive. The simple addition of an oil cooler can provide enough cooling to a modified engine so that changes to the coolant circuit can be avoided.  In modern engines using fully synthetic oil there is no need for an oil cooler from the perspective of the oil itself. Rally engines have been recorded running an entire event with accident damage limiting oil cooler flow and the oil never breaks down even though the oil goes well beyond 150degC. Subsequent engine inspection shows it to be in perfect condition.

When an oil cooler is required there are several points which must be considered. Cold running can accelerate engine wear so on road cars an oil thermostat must be used. The oil lines should be at least ½ in diameter so that there is little flow restriction. If a take-off fitting is taken from the oil filter pad, it must be of a non-restrictive design. Inserting at 90deg severely hinders flow and should be avoided. Never use a second hand oil cooler, and if your engine shows excessive wear, or if it has experienced bearing damage then the oil cooler must be replaced. Keep a close eye on the oil temp after fitting. Oil too low or to high in temp will lead to engine damage. Temp drop to 85degC will cost 1% horsepower unless you are running 0W-20 or 0W-30 oil (Royal Purple).

Oil Filters.
 - Standard filters are rarely sufficient for high performance engines.
 - There are some exceptions… e.g. certain Toyota, Nissan filters.


For any engine, modified or not, the stock filter is rarely adequate. The ideal filter should trap all particles above 5 microns without over impeding the oil flow, however, this is not possible at present. The larger the particle flowing with the oil the more damage is done. All solid material in the oil acts as an abrasive, wearing away at bearings, crank journals, tappets, cam lobes etc. A high spec engine needs superior filtering to the one offered by over the counter screw on types.

Also the standard setup may have a bypass valve to protect against situations where the filter is not changed regularly by the user. When this valve opens it allows unfiltered oil to flow and it drags the already filtered sludge to reenter the oil flow… so it has to be removed. A racing filter system shouldn’t have any bypass and therefore, must be burst proof at oil pressures up to 200psi. It must be fine enough to stop abrasive particles from flowing while not reducing oil flow to a dangerous level, especially during cold running. 

Oil Pump.

In lower stages of tune the standard oil pump will suffice if its in perfect condition. It will be possible to marginally increase the oil pressure by fitting a stronger relief valve spring or by fitting a spacer under the existing spring (like modding a dump valve). When we approach semi-race tune, a higher capacity oil pump must be used (with wider gears). It may also be necessary to replace the oil pump drive to cope with the oil pump load. Sometimes the oil pressure needs to be raised to 100psi or more to get the required oil to the bearings. However, if the right mods are made to the oil ways, then a pressure of 60 to 70psi should be the max required on an 8000rpm engine. If any failure is experienced with 70psi oil pressure then the oil ways need to be opened up and the bleed-off to the cam and lifters should be restricted. When we go beyond 8500rpm then 80-85psi can be used if necessary. But never over pressurize the oil because more power to the oil pump means less power to the flywheel.
Wet Sump Oil Surge.
Any wet sump will be prone to oil surge and it can be tough to overcome. Acceleration, braking and cornering will cause the oil to be forced away from the oil pickup pipe and air will be pumped to the bearing instead of oil. Obviously, this can lead to engine damage. To avoid oil surge, vertical baffles can be fitted in the sump. A more effective solution is to fit a horizontal baffle about 1/4in above the max oil level. Care must be taken to make sure the rods don’t hit the baffle. The baffle should fit the whole surface of the oil and allow just enough space for the oil pickup pipe to stick through. Also cut a hole for the dipstick and make sure the oil can drain back to the sump quickly. In a rally car the pick-up pipe should be placed in the middle of the sump. In a drag car the pipe should be oriented towards the back of the sump. American cars using ovals orient the pipe to the right (for anti-clockwise circuits). After fitting the baffle, watch the oil pressure closely to see that surge isn’t occurring. Data logging should be used or a big tail light fitted to the dash, otherwise intermittent oil surge might be missed.

Dry Sump.

Dry sump systems are preferred for competition engines. The oil is scavenged from the engine and piped to an external tank via an oil cooler. The oil pump has two scavenge stages drawing oil and blow-by. The oil tank stores the oil and de-aerates it. The oil pump then pumps this oil back to the engine via the oil filter. No oil surge is the primary benefit of this system. Other advantages are that the car can be lowered further without sump damage; oil leakage is reduced because of reduced oil pressure. More power is needed to drive the big dry sump pump, but there is a net gain of 3-5% in overall power because of the reduced crankcase pressure.  The disadvantages are expense and weight increase. Also, a dry sump system needs to be meticulously setup if it is to work well. The mounting of the oil tank and the size and routing of the oil lines are essential.

Oil Tank.
The size of the engine, the quantity of oil, the scavenger effectiveness and the effectiveness of the tank at re-aerating the oil all dictate the size of the oil reservoir tank. A tall round oil tank with the oil entering from the top works best. To aid re-aerating, there should be a baffle placed between the oil max and the oil inlet. The tank should be mounted close to the engine to minimize oil line length. The min radius of the bends in the pipe should be 2in.

Engine Breathers.
Large engine breathers are not requires on dry sumps. A small hose from the cam cover to the breather catch tank is adequate.  Wet Sump Breathers. To vent crankcase pressures, most engines have 1/2in hose connected to the air filter or inlet manifold. Modified engines should have 1in hose connected into each rocker cover and another one connected into the block. Position the breathers so that oil is not splashed up the hose. 

Oil Fill Level.
The sump should never be overfilled. An overfilled sump will have the crank and rods dipping into the oil on every revolution. This will foam up the oil. Too much oil will be splashed onto the cylinder walls which will consume power. If the rings cant cope with this extra oil then temps will rise and detonation will occur. A good rule of thumb is to never fill beyond ¾ of maximum and if no surge is experienced try filling to only ½ way between the min and max level.