You have a Gateway is running with 2 cores.

 The number of cores that can be used in a Cluster for Firewall-kernel on the new device with 4 cores is 4. Cluster is a feature that allows two or more Security Gateways to provide high availability and load balancing for network traffic. Firewall-kernel is a component of the Security Gateway that performs packet inspection according to security policies. The number of cores that can be used for Firewall-kernel in a Cluster depends on the number of cores available on each device in the Cluster. The Cluster will use the lowest common denominator of cores among all devices in the Cluster for Firewall-kernel. Therefore, if one device has 2 cores and another device has 4 cores, the Cluster will use 2 cores for Firewall-kernel on each device. However, if both devices have 4 cores, the Cluster will use 4 cores for Firewall-kernel on each device.