PolarStar Airsoft shows you how to install the F2 HPA engine into the Umarex/VFC MP5 in this video... "Here we cover the basic procedure for installing one of our cylinder conversion kits into the Umarex MP5 series OEM by VFC. This installation does not cover the original VFC MP5 (3rd burst) and only applies to the VFC MP5 series that uses the V2 Avalon gearbox.  

In this video we are using the F2 system but the installation is the same for the F2, F1 or JACK systems since they all use the same electronics.

Components used: F2 (V2-M4 kit), #11 Nozzle (KAC LMG)

For front wired installations (demonstrated) the original 18in. wire harness is fine. For grip wired installations, a shorter 7.5in. wire harness is recommended."