The QEV will vent the air in the firing chamber quicker, allowing you to achieve faster rates of fire, and lower the dwell on the marker as well. The Firebolt and QEV paired up really turns the extcy into one hell of a marker. The marker becomes instantly smoother, quieter, faster, and more efficient.
Check out www.projectpb.com
. They've got all of the different GoG upgrades and parts.