- Protects and cools engine
- Seals the piston rings to the
- Cleans the engine and minimizes
The basic function of
any lubrication system is to protect vital engine components by preventing
metal to metal contact and premature wear or seizure.
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.
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.
- Standardized tests exist to rate
oil based on its performance under various conditions.
indicate an oils performance in the areas mentioned, the oil makers carry out
tests and print the results on the oil bottle.
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
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.
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.
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.
Subaru 2.0L turbo, the following figures were noted…
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
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.
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.
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.
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
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.
why you have to run in an engine using straight 30 or 40 grade oil.
- The only option for high
- High viscosity index without using
- Only use oils that are blended to
- 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.
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
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.
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.
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.
oils are produced from petroleum crude oil after the distillation process has
removed most substances like tar, petrol, diesel, kerosene etc.
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…
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.
- Some additives are essential to an
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.
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.
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
must be changed before these additives are depleted.
- Change every 3000miles for
- Change every 8000miles for long
- For most performance cars, change
the oil every 5000miles.
- Change the filter every 10000miles
or sooner if worried about swarf.
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.
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
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.
oil changes can be carried out if you’re not worried about metal swarf or
about very rich mixtures thinning out the oil.
mixtures are very rich, then draining the oil and gently heating it to 100degC
can evaporate off any contamination by fuel or 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.
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
In a rally
engine, horsepower is lost above 110degC and bearings will fail above 130degC.
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.
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.
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.
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).
- Standard filters are rarely
sufficient for high performance engines.
are some exceptions… e.g. certain Toyota, Nissan filters.
any engine, modified or not, the stock filter is rarely adequate.
filter should trap all particles above 5 microns without over impeding the oil
flow, however, this is not possible at present.
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.
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.
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.
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
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).
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.
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
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.
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.
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.
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.
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
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 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.
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.
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
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.