The year 1970 introduced "the Snake and the Mongoose", a manufactured 'rivalry' between two professional drag racers calling themselves "the Snake" and "the Mongoose" for the purposes of publicity. This was notably drag racing's first major non-automotive corporate sponsor, and the beginning of the NHRA’s booming popularity with large-budget teams and championships. 1970 also introduced the first 'Silver Series', which contained three silver-painted models: the Boss Hoss, the Heavy Chevy, and the King 'Kuda, which were only obtainable through a mail-in offer that included a membership to the Hot Wheels Club. These three cars featured "supercharged" engines (featuring large Roots blowers) without hoods, and open exhaust headers, after the style of drag racing cars of the era. Popularly among children, these 'Silver Cars' were considered faster than the rest of the Hot Wheels lineup, because they were supposedly heavier than the other gravity models, but the accuracy of this claim has never been tested under scientific conditions.