Download [patched] Full Unreal Engine 427 Offline Installer Direct
The Ultimate Guide: How to Download the Full Unreal Engine 4.27 Offline Installer
Part 1: What is Unreal Engine 4.27? A Retrospective
UE 4.27 source code
If you need a portable version that you can compile yourself, you can download the from GitHub (requires linking your Epic account to GitHub). You download the code as a ZIP file.