Ive finished my beta tbi MAF code and Im using the following to calculate the base pulsewidth for the injectors:

The injector constant is based on the flowrate of one of my tbi injectors. Is this all I really need to calculate a pulsewidth? Sort of seems like Im missing something.

 

Another thing is Im not quite sure what to base the injector constant off of. Should it be one injector? Both? It seems sort of like maybe one since there is only one injector firing per DRP but my gut feeling says to use both in the calc for the inj. constant since its more of a ratio of air coming in to the overall fuel that can be delivered.

EDIT: After thinking for a minute or so each injector can theoretically stay open for up to two distributer reference periods since each injector fires twice per revolution. Since the airflow over the injectors flowrate with the AFR basically determines a duty cycle that the injector must be run at my injector constant should be double what it is now, no? Since 100% DC will be twice the current DRP giving an injector constant of 2 DRPs/injector flow rate in grams. Is this correct?

Anyway one of these has to be right, since doubling the injector constant is the only thing that gives pulse widths and duty cycles that make any physical sense. Although the more I think about it the more confused im getting.

 

Alright, I guess the injector constant should be the inverse of the total fuel flow avaliable in grams/second and the DRPs should be multiplied by two to get the total time interval that the injector has to stay open.

 

Check out this thread for the $6E calculation:

https://www.thirdgen.org/techbb2/sho...hreadid=259482

Only need to skip the part where it is multiplied by 0.01526.

The inverse AFR isn't really the inverse. It is from this calc:

ARG = 6553.6/AFR

So 6553.6/14.7 == 445

The injector flow rating is along the same lines. For double fire:

cal = Sec/gm * (256 * 5)

The kicker is that it is the number of seconds required to flow one gram of fuel. And the TBI will probably be quad fire, so halve that term.

RBob.

 

The PW from the calc you posted is exactly 1/4 of what I had from the calc. posted at the start of the thread using the injector term based on the flowrate of one injector.

Im still sort of confused on the injector constant. Basically taking the flowrate of the injector in grams per second and inverting it should give the units of second over gram, or the time in seconds it would take to flow one gram of fuel.

Now, should I use the flowrate of just one of my injectors, or both in calculating the injector constant?

Also, whats the logic behind halving the constant when doubling the firings? is it to sort of get a total ammount of time open over one revolution? {EDIT: or is it necessary because the # of DRPs in between each firing are what define the total time the injector can be open} I guess I dont understand.

Using the PW calc you posted, I get a pulsewidth of around .4 msec with around 8 gms/sec and an idle speed of 800 rpm. Does that seem right? It seems too short. I must be doing something wrong.

 

I looked at some of the hac and wrote the equation down on a sheet of paper and looked at it for a few.

I might be reaching here but:

Basically, boiling it down a bit I get

((DRP x g/sec)/2) x (.1 AFR^-1) x (sec/g of one injector x 10)

which equals:

(DRP/2 x g/sec) x AFR^-1 x sec/g

Since the flowrate is only for one injector and all of them should fire at once. Only using the flowrate of one injector to calculate the constant is effectivly like multiplying by eight, which would give:

(4 x DRP) x (AFR^-1 x g/sec x sec/g) = (4 x DRP) x %duty cycle, in double fire mode.

Is this correct?

 

ok...

Using that same logic both my calc and the one posted give the same PW when I plug in the numbers. Basically if I wanted to use the factory calc Id have to take my total fuel flow and divide by eight. Take the fuel injector constant and then divide that by two for quad firings.