Two cars of masses m1 and m2 are moving in circles of radii r1 and r2 respectively. Their speeds are such that they make complete circles in the same time t. The ratio of their centripetal acceleration is:

Since both make complete circles in same time 't'. so angular velocity is also same for both the masses.
Let ω be the angular velocity.
Then, v1 = r1ω and v2 = r2ω
Centripetal acceleration a = v²/r = (rω)²/r = rω²
Therefore, a1 = r1ω² and a2 = r2ω²
The ratio of their centripetal accelerations is:
a1/a2 = (r1ω²)/(r2ω²) = r1/r2
Hence, the ratio is r1:r2