Resolution.

[Greg Hermann]

>Hi !
>Seeking a good solution to high powered streetable engines......some
>questions pops up....
>Where is the weak link in the Efi system when it comes to resolution?
>MAP SENSOR: Going from 1 to 2bar halfs the resolution....3bar even worse.
>Is staging map sensors a posibility?
>0 to 5 volts  :  how acurate can the ecm measure the input from the
>sensors?
>Is 0 to 10 v better?  or frequensy?
>ECM: Computers ability .

There are plenty of instrument grade pressure transducers available,
Ashcroft, for one, with 0.25% full scale accuracy and better repeatability
than that,  All you gotta do is know which counter to ask for them at, and
be prepared to pay for them. Your choice of 0-5V, 0-10V, or 4-20 ma output
signal. 4-20 ma is most popular signal output for industrial
instrumentation because of wiring open/short failures being so easily
detected with it. Similar accuracy/quality/choice is readily available in
any of the other sensors commonly used in an efi system. Cost/performance
ratio is the only question as to sensors. No question that a high
horsepower engine needs more "turndown ratio" than a stocker to be decently
streetable, and that higher turndown ratios require more accurate input
data, and that the auto mfgrs are not bloody likely to spend the money
required to be any more accurate than they need to be in order to meet
emissions regs with an average HP engine!!

Real questions here are :"How many bits wide are the A/D converters in the
ecu?" and "How many mapping points does the load/rpm matrix need to
contain?" and "How many bits wide is the fuel rate calculation (and tables)
in the ecu?" and ""What is the minimum time increment to injector pw which
the ecu will implement?" and "How many bits wide does everything need to be
in order to obtain the desired level of turndown to give your high HP
engine decent street manners?"

Staging injectors, and rising rate fuel pressure control are certainly a
help, particularly if there are fuel rail pressure and temp inputs to the
ecu for fuel rate corrections on the fly!

Regards, Greg