Pennzoil: Popular Science October 1975
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With the evolution of the car must come the evolution of what we put in our car. With the introduction and popularity of the American muscle car of the 1970s we see 20W-50. A heavier weight oil that is relatively viscous and thick and can help increase oil pressure. It's the best oil for those of us who have vehicles in "high-stress activities"… like tearing up the local ¼-mile racetrack!
Today, Pennzoil continues to pursue the latest in motor oil advancements. See what's new today at Pennzoil.com: http://www.pennzoil.com/motor-oil/