Speed News Vol. 1 Issue 6 July : Page 61
do its job very well when it fl ows poorly. Multi-viscosity oils offer better fl ow and lubrication at start-up and made the practice of changing oil viscosity grade with the seasons obsolete.” As Barker explains it, the second number is what he refers to as the “major viscosity grade,” and is determined by the measured viscosity at a certain temperature. The “W” number is the “winter” number and represents the cold fl ow ability. All these numbers and measures are defi ned by the Society of Automotive Engineers. For a racer’s purposes, the second number is more important. Barker notes that it is more accurate to think of different multi-viscosity grades in groups – 0W-30, 5W-30 and 10W-30 would all be “multi-viscosity 30-weight” oils. The second number is more important because races are seldom conducted at below-freezing temperatures, and racers rarely hop in the car, fi re it up and immediately head out on track like someone going to work on a chilly morning. Most racers are going to let the engine come up to temperature before they start putting any stress on it. There are gains to be had by 61
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