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Så... Någon som har bromsbänkspapper på sin motor med flera olika oljor? Eller har ni inte tänkt på det?
VISCOSITY AND HORSEPOWER
For example, my usual oil of choice for road engine s is Mobil l, 5W-50 grade viscosity. It provides a very high level of engine protection first and foremost. There are one or two other oils about which are similar, or even marginally superior in this regard, but they are not so readily available and they are considerably more expensive. AIso, these are down on power and show increased fuel consumption. The horsepower king, while still providing adequate engine wear protection is the OW-40 grade of Mobil l. As you can see in Table 20.1, when tested against a large number of oils, including some with lower viscosities, it was a clear winner. In comparison with Mobil l 5W-50 it has slight fuel economy benefits, too, in the order of 1-1.5% under highway cruise conditions. Therefore, when it is maximum hp that I am after OW-40 tri-synthetic is the grade I choose. However, it allows slightly more engine wear than 5W-50 and if the power advantage is to be maintained it has to be changed more frequently as it thickens up more rapidly because of a significantly higher evaporation rate.
In recent times the idea has been that low viscosity oil, being thinner, will always help an engine make more hp. However, viscosity is only half of the picture - friction modifiers are the other half. You would think that a light oil would always guarantee a hp benefit but, as you can see when you compare the two Castroi products, that isn't the case. The thicker lOW-60 Castroi R synthetic made more maximum power than most of the oils tested, while its thinner sibling was close to the bottom in overall hp. Clearly, if we are looking to gain hp from a particular type of oil, then there is more to it than simply choosing one with a very low viscosity.
Table 20.1. Synthetic OH Horsepower Comparison
Mobil l, Shell Helix Ultra, Castroi R, Amsoil, Mobil l, *Royal Purple, BP Visco, Castrol SLX
5W-50 5W-40 lOW-60 lOW-40 OW-40 5W-40 OW-30
Rpm
3000 143.2 144.8 140.5 141.2 142.9 140.7 139.8 138.6
4000 202.9 201.3 203.6 203.2 202.4 202.5 202.3 201.2
5000 263.1 262.5 262.4 262.5 266.6 262.8 261.5 260.8
5700 290.4 290.0 293.3 290.7 297.4 294.0 289.9 289.7
6200 304.3 303.5 306.5 305.6 311.2 308.7 303.6 305.1
7000 280.7 278.9 282.7 281.4 288.1 284.5 279.1 282.4
*Royal Purple does not state a viscosity rating, but lab testing shows it to be in
the OW-20 to OW-30 range.