Yes, the distance from the exhaust flange matters in absolute terms
for EGT. Let's say they are all at 4 inches, then the absolute temps
should be pretty close assuming zero difference in probes.. If they differ
in location you may get quite different EGT readings. But, that is
not important.
In order for a balanced prop/engine to run smoothly, each cylinder should
be producing the same horsepower. Thus, F/A mixture and ignition timing
must be the same for each cylinder (along with good rings and proper valve
operation). Also note that there is a hole in each injector body to allow
air to be added to the injector stream to improve atomization. Also note
that in NA engine setups there are pressure differences in the upper
cooling plenum that may cause atomization to be different for each injector
based on location. In turbo's engines, upper deck air at the same flow and
pressure is fed to shrouded injectors so that the air distribution is equal and
at a pressure higher than ambient upper cowl pressure. I.E. 30" MAP at
18000 MSL. But I digress.
Well, suppose timing is fixed (or variable based on MAP and RPM) and
air distribution is what it is (may be different at WOT or partial throttle -
especially in carbureted engines). Then the thing that is possible to
control is the fuel flow to each cylinder via tailored injector
size. HP can be equalized this way. HP can be indirectly measured by
fuel flow at peak EGT per cylinder (the GAMI test). Hmmmmm, maybe that's
direct measurement. Anyway, if the FFs at peak EGT are different (say
greater than .5 gph) then the cylinders are running at very different HPs, ergo
not smooth.
Personal note: If you have to get different flow injectors make sure
you have performed the tests in conditions similar to cruise (but at 75% power
or less) - where your smoother engine will spend most of its time, whether
running ROP or LOP.
Scott Krueger