What do those numbers on the rad cap mean? On my Crx 91, it is 0.9 .
On my Civic 1992, it is 1.1

So, can I interchange those caps to solve my coolant overflow from the overflow containter while on the race track. There is no problem when I drive on the highway or the city.

 

That's the pressure setting for the cap to release pressure out to the reservoir.

0.9 bar = 13 psi
1.1 bar = 16 psi

Switching to a higher-pressure cap will prevent it from venting too soon. But the higher pressure might not be good if your radiator or hoses are designed for a pressure of 0.9 bar.