My friend JP is hard at work finding all the port openings we need that haven't gotten completely documented yet, and here's a new one. (By the way, these all ARE working their way into TechNet, it will just take a month or two probably for them to find their way there). If you have firewall turned on between your SharePoint servers, then you should know that you need to open TCP on port 808 on your servers that are running Search components. Thanks again JP for finding another golden nugget here.
Have a look at this post "SharePoint 2013 Ports, Proxies and Protocols - An Overview of Farm Communications" it contains all the ports you need to open
Already on TechNet - technet.microsoft.com/.../763613ac-83f4-424e-99d0-32efd0667bd9(v=office.15).aspx
Thanks for the comments folks. Both of the links above though reference port 808 only for WCF communications. The purpose of this posting is to point out that it's required on servers where you only have one or more search components running.