Injector shrouds

[DGraber460 at aol.com]

Yesterday I pulled the intake manifold to replace a missing EM stud and  
figured while accessible I would check the injector shrouds etc.
I noticed that I have in my parts selection 3 different types of injectors  
and shrouds. Short but large, Long and slimmer with smaller threads, and Brass  
combo long and large barrel. Each type, which I assume is an update, looks to 
 increasingly impinge on the intake tract, thus reducing flow.
Any info or specs for the various types, their applications, and  advantages?
Curious and puzzled.
And FWIW still vapor locking like a bitch!
Cursed year-round oxy fuels!! Any chemical engineers know how to  
inexpensively raise the boiling point of gasoline?
 
Dennis
Denver