Injectors

[Greg Hermann]

>> What computer could I use for multiple(dual) port injector setup like
>> that?
>
>Well, I wouldn't want to design or build a system based on one or two
>big-ass 100lb injectors.  If one gets stuck closed, you'd lose 1/2
>your fuel and lean out.  Underboost, you'd detonate something fierce.
>If the reverse happened, where one injector got stuck open, you'd have
>a flood, possibly a fire if the engine even runs at all.
>
>This is one of the things I do like about multiple injectors, spread
>around the intake runners, i.e. one injector per cylinder.  Fire 'em
>sequentially, batch, a combination of the two, whatever, however if
>one injector goes bad, on a V8 engine you could in theory limp home
>with crappy performance.  But, you more than likely could get home.
>
>Also, if you calculated out that you need two (see dual above) 100lb
>injectors, that's 200lbs worth of injector performance at an 80% duty
>cycle, divided by "banks" or "cylinders" depending how you want to
>fire them, and you have smaller, less costly injectors.
>
IF you are going to go with staged injectors, the best plan is to size the
primaries for 1/3 of the fuel flow, and the secondaries for two thirds of
it-- If you need 90 lb. injectors to feed the engine--use 30 lb primaries
and 60 lb. secondaries. This will give you by far the most stable control,
with the widest dynamic range. A decent definition of dynamic range for
these purposes is maximum fuel flow rate divided by minimum fuel flow rate
(per unit time).

If your engine is going to make 1000 HP at full throttle, and say requires
maybe 8 HP to idle and run its accessories at idle, the turndown ratio, or
dynamic range you will need on your injection system is 1000/8, or 125 : 1.
If you don't have that much turndown ratio available, the engine won't idle
worth $#%!!

Too much bandwidth involved to explain why this stuff works this way,
suggest consulting a text on control theory if curious beyond just doing it
as described on a cookbook basis. Control of Boilers, by Sam Dukelow,
published by Intrument Society of America is a good place to start on basic
control theory for any interested, Sam's book is heavy on description and
pretty light on math--for those who feel math deprived, there are LOTS of
control theory texts that would cure your math craving in about five pages!

There is a Brit outfit (DCA????? or something like that) that makes an ecu
that can be optioned to run two injectors per hole on a V-8. And its price
is under $2000, I think fairly far under--just don't recall HOW far. (That
price is before you get the wide band O2 option for it.)

Regards, Greg