In 1975 when new cars had catalytic converters and required unle

来源: 坚茂 于 2015-09-18 10:18:53 [] [旧帖] [给我悄悄话] 阅读数 : (252 bytes)

In 1975 when new cars had catalytic converters and required unleaded fuel, the engines started being built with hardened valves. The hardening was needed to compensate for the "lubricant/cushion" effect that the lead once provided.

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