Green’s Dictionary of Slang

(US) a car.

1954		Hepster’s Dict. 6: Kemp – Car.
1959		A. Zugsmith Beat Generation 63: Hop in my kemp.
1971–2		C. Shafer ‘Catheads [...] and Cho-Cho Sticks’ in Abernethy Bounty of Texas (1990) 208: kimp, n. – a car (1950s).