Pulse Width vs # squirts vs. injector sizing and count

[ptegler]

OK... been playing with this for awile.
quick background and sys config....
in line 6 cyl engine. under two different setups.
1) 6 injectors - TPI setup - common plenum with one throttle body
2) 2 injectors, one each TB feeding 3 cyls each, via twin trottle bodies
(standard dual carb style setup of many British cars)

ReQ_fuel #'s vs number of pulses per cycle is getting me confused here now. If I set up 6 inj. (6 x 14# injectors) on 6 ports (TPI) should it be 3 injections per engine cycle?.... or ????

So if I go to the two throttle bodies, with one injector per body each feeding 3 cyls (2 x 42# injectors) should it be 6 squirts per engine cyl?
???

OK... let's ask this more simply....
What's the opinion(s) or proper # or squirts for a 6 cyl engine per cycle,
and is it better running simultaineous, or alternating with how many suqirts per cycle?
Then if I go to two injectors on 3 cyls each...same question...
# of squirts per cycle? alt/siml??
HELP...confusing myself now here.

ptegler

[PSIG]

"Squirts" is the total number of injection signals the MS sends out per engine cycle. Example: 6 cylinder engine, TPI with 6 injectors set to "1 squirt simultaneous" - will cause ALL the injectors attached to INJ1 and INJ2 to squirt ONCE at the same time, every 2 crank revolutions (one cycle).

The same engine setup with "2 squirts alternating" will cause one bank of injectors (3 of them on INJ1) to squirt at the same instant and then the other 3 on INJ2 to squirt one crank revolution later. Still ONE squirt from EACH injector, per engine cycle, but the total squirts divided into two alternating batches.

However, "2 squirts simultaneous" causes all the injectors to fire TWICE each cycle. Yes, it's confusing.

I hope that makes more sense.

David

[ptegler]

Thanks for the input. Yep...what you defined, I do already understand.

On an in-line 6 cyl, (AKA: a Triumph 6 cyl) the firing order is
1-5-3-6-2-4 So in my twin throttle body setup (replicating a stock twin carb setup) the front 3 and rear three cyls are on seperate carbs/ or now, throttle bodies. So I'd be running one injector on each body. One for the front 3 cyls and one for the rear three cyls.

Since the firing order would be Front-rear-front-rear-front-rear-front-rear, I'm trying to determine the best method of firing the two injectors.
Hence my question concerning alternating squirts with one/two/three/four squirts per cycle.

So I'm still a bit in the dark here as to the best scenerio.

[PSIG]

Others have found that increasing the number of injections is not always a necessity with TBI due to the effect of the plenum and runners on fuel mixing and distribution. See http://msefi.com/viewtopic.php?t=9131

You'll have to figure maximum possible injections by calculation. The problem is, you want fuel feed as consistent and continuous as possible in a TBI setup; but you run out of time to open and close each injector several times/cycle and still get enough flow at max demand. Single TBI V8's run fine at off-idle on 2/alt but idle better on 4/alt or 4/simul. Perhaps yours won't need as many either.

Use the calculator here http://www.megasquirt.info/v22manual/mfuel.htm#reqfuel or for teh masochist in you - try calculating your available injection time (at both min and max rpm), subtract 4.2ms (3x1.4ms for 3 minimum GM TBI open & close events @ .7ms) and divide the remaining time by # of squirts to see if you can get min/max fuel in there in the time that's left - and what size injectors you'll need to do it. Your injectors sound huge for the application. Maybe some Geo TBI injectors are in your future

There. That should be as clear as mud...
David