Increase use core by splunk

Hi all, I am using Heavy forwarder (splunk version 8.0.1 and os-windows) to ingest .zip log files but I could see very less cores are getting used which is around 2 to 3 .although Heavy forwarder has 8 cores available . So how can I make setting to use all cores by splunk. Also I have increased parallelingestion pipelines to 2. So is there any setting by which I can increase cores used by splunk? Thanks,