RE: [ST] Why Synthetic Oil?

["Masiak, Richard" <Richard_Masiak@xxxxxxxxxxxxxxxx>]

With all the discussion about oil lately, here's an interesting article I
found a while back.  Since I can't put an attachment and I don't have the
link so I've pasted the text.  Hope y'all don't get angry with the length,
here it is:

The SAE Business (American Society of Automotive Engineers)

Viscosity is the force required to shear the oil at a certain speed and
temperature. Oils work because they have viscosity; the drag of a rotating
part pulls oil from a low-pressure area into a high pressure area and
'floats' the surfaces apart. This is called hydrodynamic lubrication, and
crank bearings depend on it. In fact, a plain bearing running properly shows
literally no metal-to-metal contact. Experimental set-ups have shown that
electrical current will not flow from a crank main bearing to the shells.
Also, the energy loss due to friction (the co-efficient of friction) is
incredibly low, around 0.001. So for every kilogram pulling one way,
friction fights back with one gram. This is very much better than any 'dry'
situation. For example, the much over-rated plastic PTFE has a co-efficient
of friction on steel of 0.1, 100 times worse than 'ordinary' oil.

Oil viscosities are accurately measured in units called 'Centistokes' at
exactly 100 C. These fall into five high temperature SAE categories:- (<
means 'less than') 
SAE No.	 20	 30	 40	 50	 60
Viscosity range 	 5.6 - <9.3	 9.3 - <12.5	 12.5 - <16.3
16.3 - <21.9	 21.9 - <26


A decent quality oil usually has a viscosity that falls in the middle of the
spec, so a SAE 40 will be about 14 Centistoke units, but SAE ratings are
quite wide, so it's possible for one 40 oil to be noticeably thicker or
thinner than another.

So, a good oil must be quite low in viscosity even in the cold, so that it
gets around the engine in a fraction of a second on start-up. On the other
hand, it must protect engine components (piston rings for example) at
temperatures up to 300 C without evaporating or carbonising, and maintain
oil pressure. 

When the polymer modified multigrades appeared, a low temperature range of
tests were brought in, called 'W' for Winter (no, it doesn't mean Weight!).
These simulate cold starts at different non-ferrous monkey endangering
temperatures from -15º C for the 20W test to a desperate -35º C for zeroW
(0W). So, for example, a SAE 5W/40 oil is one that has a viscosity of less
than 6600 units at -30º C, and a viscosity of about 14 units at 100º C. Now,
those who have been paying attention will say "Just a minute! I thought you
said these multigrade polymers stopped the oil thinning down, but 6600 to 14
looks like a lot of thinning to me!" Good point, but the oil does flow
enough to allow a marginal start at -30º, and 14 is plenty of viscosity when
the engine is running normally. (A lot more could damage the engine, so we
don't recommend the use of 24 unit viscosity SAE 60 oils.) The vital point
is, a monograde 40 would be just like a wax candle at -30º C, and not much
better at -10º C. It would even give the starter motor a fairly difficult
time at zero. (At 0º C, a 5W/40 has a viscosity of 800 but the mono 40 is up
at 3200.) 

Another basic point about wide range multigrades such as 5W/40 or 0W/30 is
that they save fuel at cruising speeds, and release more power at full
throttle. But complications arise...








The Synthetic Myth

What do we mean by the word 'synthetic'? Once, it meant the 'brick by brick'
chemical building of a designer oil, but the waters have been muddied by a
court case that took place in the USA a few years ago, where the right to
call heavily-modified mineral oil 'synthetic', was won. This was the answer
to the ad-man's dream; the chance to use that sexy word 'synthetic' on the
can... without spending much extra on the contents! Most lower-cost
'synthetic ' or 'semi-synthetic' oils use these 'hydro-cracked' mineral
oils. They do have some advantages, particularly in commercial diesel
lubricants, but their value in performance engines is marginal.

True synthetics are expensive (about 6 times more than top quality mineral
types). Looked at non-basically, there are three broad categories, each
containing dozens of types and viscosity grades:- 

1) PIB's (Polyisobutanes)
These are occasionally used as thickeners in motor oils and gear oils, but
their main application is to suppress smoke in 2-stiokes. 

The two important ones are:-

2) Esters
All jet engines are lubricated with synthetic esters, and have been for 50
years, but these expensive fluids only started to appear in petrol engine
oils about 20 years ago. Thanks to their aviation origins, the types
suitable for lubricants (esters also appear in perfumes; they are
different!) work well from -50º C to 200º C, and they have a useful extra
trick. Due to their structure, ester molecules are 'polar'; they stick to
metal surfaces using electrostatic forces. This means that a protective
layer is there at all times, even during that crucial start-up period. This
helps to protect cams, gears, piston rings and valve train components, where
lubrication is 'boundary' rather than 'hydrodynamic', i.e. a very thin non
pressure-fed film has to hold the surfaces apart. Even crank bearings
benefit at starts, stops, or when extreme shock loads upset the hydrodynamic
film. (Are you listening, all you rally drivers and off-road fanatics?)

3) Synthetic Hydrocarbons or PAO's (Poly Alpha Olefins)
These are, in effect, very precisely made equivalents to the most desirable
mineral oil molecules. As with esters, they work very well at low
temperatures, and equally well when the heat is on, if protected by
anti-oxidants. The difference is, they are inert, and not polar. In fact, on
their own they are hopeless 'boundary' lubricants, with less load carrying
ability than mineral oil. They depend entirely on the correct chemical
enhancements. 

In fact PAOs work best in combination with esters. The esters assist load
carrying, reduce friction, and cut down seal drag and wear, whilst the PAOs
act as solvents for the multigrade polymers and a large assortment of
special compounds that act as dispersants, detergents, anti-wear and
anti-oxidant agents, and foam suppressants. Both are very good at resisting
high-temperature evaporation, and the esters in particular will never
carbonise in turbo bearings even when provoked by anti-lag systems.








Even More Power!

The place to look for extra power is in that 6% lost as oil drag. In a
well-designed modern motor, the oil doesn't have to cover up for wide
clearances, poor oil pump capacity or flexy crankshafts, so it can be quite
thin. How thin? Well, take a look at these dyno results.

A few months ago we ran three Silkolene performance oils in a Honda
Blackbird motorcycle. This fearsome device is fitted with a light, compact,
naturally aspirated 1100c.c. engine which turns out 120+ BHP at the back
wheel. The normal fill for this one-year-old engine was Silkolene Turbolene
GTI 15W/50, so the first reading was taken using a fresh sump-full of this
grade. (The dyno was set up for EEC horsepower, i.e. pessimistic.)

Turbolene GTI 15W/50
Max power 127.9 BHP @9750 rpm 
Torque 75.8 ft-lbs @ 7300 rpm 
After a flush-out and fill-up with Pro S 5W/40 the reading were;
Pro S 5W/40
Max power 131.6 BHP @ 9750 rpm 
Torque 77.7 ft-lbs @ 7400 rpm 

Then we tried a new experimental grade, Pro R 0W/20, yes, 0W/20. This wasn't
as risky as you may think, because this grade had already done a season's
racing with the Kawasaki World Superbike team, giving them some useful extra
power with no reliability problems. (But it must be said, they were only
interested in 200 frantic miles before the engines went back to Japan.)

Pro R 0W/20
Max power 134.4 BHP @ 9750 rpm
Torque 78.9 ft-lbs @ 7400 rpm 

In other words, 3.7 BHP/2.9% increase from GTI to Pro S, a 2.8 BHP / 2.1%
increase from Pro S to Pro R, or 6.5 BHP / 5% overall. Not bad, just for
changing the oil, eh? More to the point, a keen bike owner would have paid
at least £1000 to see less improvement than this using the conventional
approach of exhaust / intake mods, ignition re-mapping etc.

Am I recommending 0W/20 for high performance engines? Well, perhaps not! The
Pro S 5W/40, which is a 'proper' PAO/ESTER shear-stable synthetic, will look
after a powerful engine better than a heavier viscosity 'cave at the back'
conventional oil, and provide a useful few extra BHP. (On the other hand,
the 0W/20 was very thoroughly developed to give good anti-wear protection. I
think I was on 'Blend 6' before Kawasaki was happy with it!)

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