Batch Fire Timing and Firing Order

BBShark

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I am re-wiring the fuel injector harness for a Commander 950 MPFI setup. This is a batch fire system where 4 injectors fire and then the other 4 fire. So Holley recommends that the 2 injector "batches" be cylinder 1&3+6&8 and the next batch is 2&4+5&7.

I'm probably splitting hairs here but, considering the firing order is 18436572, the injector timing seems like it should be 1&3+4&8 and 2&6+5&7. This is still bank to bank so I don't get why 6 and 4 are swapped.
 
cleanliness of wiring?

if you ever switch to sequential firing, you'd have to swap the order to what you suggest.
 
The batch firing order for a early analogue computer DPFI was 7218 on one batch and 4365 on the other batch......so I note that a TPI was left and then right bank.....

so the 4 corners, then the 4 center cylinders.....

then to switch to left/right banks....

then I note the timing of air/fuel suspension....600 rpm....5 pulses of injection per second....MAX time per second is therefore 200 ms.....

hard for me to believe that in 200 ms, MAX time, that there is any time at all for the fuel to have any reaction with the short passageway into being past the valve to chamber.....and the injector firing a couple inches away....


another way to say, in a batch fire system, I don't honestly think it matters.....

and long as we are not doing the diesel trick of direct injection.....I honestly fail to see how sequential brings much to the table....really gotta be splitting hairs there.....:skeptic::tomato:
 
I hope this wont evolve into the merits of batch fire vs. sequential. Batch fire is what I have and I am merely making an observation about the logic behind it when it could easily be configured the other way.

The batch firing order for a early analogue computer DPFI was 7218 on one batch and 4365 on the other batch......so I note that a TPI was left and then right bank.....

so the 4 corners, then the 4 center cylinders.....

Gene, this injector timing (if you put the numbers together, 7218 and 4365) is the standard GM firing order. So, why does Holley suggest a different injector timing by swapping 6&4?
 
I hope this wont evolve into the merits of batch fire vs. sequential. Batch fire is what I have and I am merely making an observation about the logic behind it when it could easily be configured the other way.

The batch firing order for a early analogue computer DPFI was 7218 on one batch and 4365 on the other batch......so I note that a TPI was left and then right bank.....

so the 4 corners, then the 4 center cylinders.....

Gene, this injector timing (if you put the numbers together, 7218 and 4365) is the standard GM firing order. So, why does Holley suggest a different injector timing by swapping 6&4?

Damn if I know, but I remember some cam timing changes swapping a couple cylinders but can't recall the #s right quick.....

All I can say is that when totally abjectly frustrated over the POS TPIS ZZ9 cam and the insane habits the engine had, one day it was FINE, next day the thing ran like crap.....mostly it ran like crap.....and over YEARS it drove me krazy.....

so that aside,....in that never ending search, one of the tricks I did was to change the injector batch sequence from one bank to the 4 corner/four center setup.....noticing NO difference over some weeks of operation.....

so a long time later I finally installed a cam from a dear friend, and found the fucked up cam from TPIS, who managed to make a defective ROLLER CAM that wore in such a way that cost me much problems over YEARS....


BUT the point of this experience is....that batch firing order had nothing to do with the operation of the engine....

go figger, MY observations over the time suspended and physics in the intake passage and so forth, are mine....I just can't visually figger why it should matter much....

:shocking::beer:
 
I wonder if it has something to do with the position in the cycle. 1 and 6 are both TDC at the same time but in different phases of the 4 strokes? No idea.
 
I am re-wiring the fuel injector harness for a Commander 950 MPFI setup. This is a batch fire system where 4 injectors fire and then the other 4 fire. So Holley recommends that the 2 injector "batches" be cylinder 1&3+6&8 and the next batch is 2&4+5&7.

I'm probably splitting hairs here but, considering the firing order is 18436572, the injector timing seems like it should be 1&3+4&8 and 2&6+5&7. This is still bank to bank so I don't get why 6 and 4 are swapped.

Just curious about an item before I throw out an opinion ('cuz you know what they say about opinions). Batch fire systems (generally) don't have a cam sensor, so the batch firing happens at a different cylinder "pair" , or crank position, every time the ignition is cycled. Your system doesn't have a cam sensor, correct?
 
Mike, Good question. There is no cam sensor or crank trigger. I'm not sure how (or if) there is a scheme to syncronize events. I know it alternately sprays fuel on the back of the intake valve.
 
I am re-wiring the fuel injector harness for a Commander 950 MPFI setup. This is a batch fire system where 4 injectors fire and then the other 4 fire. So Holley recommends that the 2 injector "batches" be cylinder 1&3+6&8 and the next batch is 2&4+5&7.

I'm probably splitting hairs here but, considering the firing order is 18436572, the injector timing seems like it should be 1&3+4&8 and 2&6+5&7. This is still bank to bank so I don't get why 6 and 4 are swapped.

Just curious about an item before I throw out an opinion ('cuz you know what they say about opinions). Batch fire systems (generally) don't have a cam sensor, so the batch firing happens at a different cylinder "pair" , or crank position, every time the ignition is cycled. Your system doesn't have a cam sensor, correct?

Mike, Good question. There is no cam sensor or crank trigger. I'm not sure how (or if) there is a scheme to syncronize events. I know it alternately sprays fuel on the back of the intake valve.

Well, yeh, like my speed density late 80/ early 90's stock 1227730 system, the thing knows to fire something off the dizzy, it's the only possible way, it talks to the dizzy for advance information off that knock sensor....so I remember taking a hammer and hitting the side of the block back when it was running crappy cam, and watching the thing retard the timing.....so the only way it knows to fire is fire a batch on the first call for spark, count to 4 and fire again....like I say 200ms MAX time for fuel suspended on top of the valve, and that's at 600 rpm, idle speeds.....

so not start the debate, but I have never understood the sequential argument as being somehow better, I can't get over the small time intervals in my mind.....In other words, can't see the physics, I can understand the theory fine, but remain shocked that it could ever be measured.....I would think the damn engine condition would make more difference than ANY thing of that nature.....

:rolleyes::clobbered:
 
The distributor provides the erference signal for a batch fire system, also these fier twice per cycle...not once.You can Probably set it to single fire mode but that's only used when injectors are so large that the fuel delivery is too large @ minimum pw in double fire mode.
 
The distributor provides the erference signal for a batch fire system, also these fier twice per cycle...not once.You can Probably set it to single fire mode but that's only used when injectors are so large that the fuel delivery is too large @ minimum pw in double fire mode.

So my setup DOES IN FACT fire twice per cycle?? interesting, wonder why?? I guess better atomization with a smaller flowing injector??? correct??

wonder why not 4X then?? or even 8X as in every pulse gives another squirt....???:crutches:
 
OK think I get it. The idea behind Holley's injector pulse order is this. They are trying to get an equal amount of fuel delivered from the fuel rail(s). In my case, I am talking about a BBC with one central fuel rail but that is the exception, most are 2 rails, one on each bank. And you want only two injectors open per rail and you want to alternate front to back of the rail.

So, fuel distribution is more important than syncronized ignition. I would have tought that the flow rates were small enough that pressure drop would not be a concern. I still question this. I don't see any drop in fuel rail pressure on other engines when you slam the throttle.

Jeez, how dificult would it have been to at least phase these events so it's optimized. The ECU already knows RPM, duh!
 
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OK think I get it. The idea behind Holley's injector pulse order is this. They are trying to get an equal amount of fuel delivered from the fuel rail(s). In my case, I am talking about a BBC with one central fuel rail but that is the exception, most are 2 rails, one on each back. And you want only two injectors open per rail and you want to alternate front to back of the rail.

So, fuel distribution is more important than syncronized ignition. I would have tought that the flow rates were small enough that pressure drop would not be a concern. I still question this. I don't see any drop in fuel rail pressure on other engines when you slam the throttle.

Jeez, how dificult would it have been to at least phase these events so it's optimized. The ECU already knows RPM, duh!

I have a length of FI hose from Aeroquip running from the OEM 3/8 fuel line into the LT1 fuel rail....and if I put my hand on that double wrapped mesh grenade proof hose, I can feel the pulses at idle.....I can't see anything, but sure can feel it.....I don't see how that hose can have that much pressure flex to it, but it does....:shocking::ill:
 
Taken from the Tuning manual:
"Each group or pair of group is offset by one
crankshaft revolution. This arrangement allows for an injector timing selection that eliminates metering the fuel into an
open intake valve. Holley uses this type of system"
 
Taken from the Tuning manual:
"Each group or pair of group is offset by one
crankshaft revolution. This arrangement allows for an injector timing selection that eliminates metering the fuel into an
open intake valve. Holley uses this type of system"

Does this say what I think it says? They are NOT injecting fuel when the intake valve is open? Now I'm completely confused, seems like that would be the best time.
 
Taken from the Tuning manual:
"Each group or pair of group is offset by one
crankshaft revolution. This arrangement allows for an injector timing selection that eliminates metering the fuel into an
open intake valve. Holley uses this type of system"

Does this say what I think it says? They are NOT injecting fuel when the intake valve is open? Now I'm completely confused, seems like that would be the best time.

The Holley manual doesn't make any sense to me. As the system is not an SFI, it's a semi-crapshoot when the fuel gets injected (relative to a specific cylinder). At any point in the crank's revolution there's going to be two cylinders that are at some point in their intake stroke. It seems to me that one or two of the cylinders are going to get the second half of their fuel allotment when the intake valve is open.

Or am I missing something in the injection details?
 
Taken from the Tuning manual:
"Each group or pair of group is offset by one
crankshaft revolution. This arrangement allows for an injector timing selection that eliminates metering the fuel into an
open intake valve. Holley uses this type of system"

Does this say what I think it says? They are NOT injecting fuel when the intake valve is open? Now I'm completely confused, seems like that would be the best time.

The Holley manual doesn't make any sense to me. As the system is not an SFI, it's a semi-crapshoot when the fuel gets injected (relative to a specific cylinder). At any point in the crank's revolution there's going to be two cylinders that are at some point in their intake stroke. It seems to me that one or two of the cylinders are going to get the second half of their fuel allotment when the intake valve is open.

Or am I missing something in the injection details?

I think it's a crap shoot....U R correct....

:clobbered:
 
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