The "pink slip" is the paper showing ownership of the vehicle. Without it, you don't own the car. "Racing for pinks," as we probably all know by now, means racing to win the other competitor's vehicle. The winner will own both cars.

In the "Little Deuce Coupe" song, the singer is saying if you don't believe it's fast, I'll bet it against anything you have.

I reckon your mixing up "pink slip" and "fixed slip";sounds roughly the same if you sing it.
A "fixed slip daddy" referred to the rear axle of the deuce coupe. The weirdly named "DADDY LONG LEGS" was a Californian engineering company specialising in transmissions and rear axles for performance cars of the day.A fixed slip differential got the power down smoothly and safely and was a "must have "for the serious street racer: it still is. "And she purrs like a kitten till the "lake pipes" roar"falls into the same category. Exhaust pipes by a firm called LAKER. These were sixties big names in American car tuning.

In California, the vehicle title is pink (or was in the 1960's). So the song is saying "What's more, she's mine." It might have meant "free and clear", too. I'm not sure. Racing for pink slips was wagering your ownership of your car on the outcome of the race, as you mentioned in the previous answer.

The Pink Slip is the owner's slip - Back in those days in CA anyway- when you finished paying for your car you got the "Pink Slip" for the car- It was paid for in full- and it was pink. So they are saying they also have the pink slip or owner's slip.

In California, the certificate of ownership (Title), used to be pink. In the late 1950s and in to1960s it was common for the guys with the hottest cars to challenge someone to "drag for pink slips." Meaning the loser not only lost the race, but also the car.

A "pink slip" in automotive terms refers to the title of the car.

The song is "Little Deuce Coupe" by "The Beach Boys"

"She's got a competition clutch with the four on the floor
And she purrs like a kitten 'till the lake pipes roar
And if that ain't nough to make you flip your lid
There's one more thing I got the pink slip daddy"

A "Pink Slip" is a racing competition, where, the winner gets the losers car, but the winner keeps his own car. This can also be gambling (racing for money).

Searching for the definition, all I can find is, "A notice from [your] job, telling you that you are unemployed." (A.K.A, been fired!).

This may be wrong, but, because of the songs theme, I think it is the first one!

It is "pink slip." Case closed. And it does mean "ownership" of the car. And we called it racing "title for title."

Ownership papers for the car.

The certificate of ownership of a motor vehicle in California (title) was a pink document issued to the owner or mortgage holder by the DMV. When a vehicle was free and clear of encumberance it was registered in the owner's name and released to the owner. The line in the song means that the "Little Deuce Coupe" is paid for and the owner has the title which he will offer as a wager against another person's car in a street race...as was the custom in the 1960's. Customarily, the winner gets title to the loser's car at the end of the race.