WHY TWIN (DUAL) FUEL RAILS?
For engines with a very high output per cylinder, it is sometimes advantageous to run 2 injectors per cylinder. You would normally have one primary and one secondary injector per cylinder.
The primary injector is used throughout the engines' operating conditions. The secondary injector is used under high load conditions where the primary injector cannot provide enough fuel flow by itself.
This can be especially true when using E85, as you generally need to flow 30% - 40% more E85 than normal petrol to produce the same amount of power due to E85s' lower specific energy.
NOTE: If you are going to run E85, make sure your entire fuel system including your fuel injectors, fuel pumps, fuel lines, and filters are all E85 compatible.