Interesting info on B3702 Injection timing

[Gelf VXR]

I heard back from the garage carrying out my cam and head install today, they said the idle is smooth. This is stock LS2 and tune with LS7 injector calibrations with L92 heads, comp 216/229 cam.

One interesting difference I noticed with the injector calibrations for the injector timing when you add the ECT + RPM advance tabes, from 0 to 1020 rpm. Apart from that identicle.


The LS7 calibration has 20 to 65 degrees more advance than the LS2.

[Gelf VXR]

Bumping this old thread, it seems I made an error thinking injector advance was referenced to TDC on the power stroke

Stock LS2

Engine hot

IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC

The injector couldn't possibly open as the inlet valve closes, could it?, the advance must be referenced to TDC on the induction stroke inlet valve opens. The injector opens 220 BTDC inlet opens / 140 ATDC ignition stroke, just after/during the combustion event, spraying onto the closed and very hot inlet valve, cooling it in the process and vaporising the fuel. Ref: RC engineering in this thread http://www.chevytalk.org/fusionbb/sh...hp?tid/199007/

The injector open & close time in relation to crank angle is variable depending on rpm (opens) and injector duty cycle (closes), there doesn't seem to be any fixed correlation to the inlet or exhaust valve timing events other than the injector closes variable time before the inlet valve opens, it is only when high rpm and 85% duty cycle is reached that the injector close time will be after the inlet valve has opened. See attached

For example at say injector duty cycle 85% is equal to 15ms @6400rpm, 1ms = 38 crank degrees, 15 x 38 = 570 degrees

720 - 570 = 150 degrees, the duration of stock cam is 204 degrees, its impossible for the injector to open and closed during the inlet valve closed duration.


Intuitively I would think that if there is any tuning to be done to injector timing its with regard to opening the injector at the optimum crank angle for the combustion event when the inlet valve is hottest to make the most of vaporisation and time before the inlet valve opens?? If your injectors are open when the inlet valve is open, time for larger injectors???

[joecar]

Hi Gelf,

Injectors are not necessarily fired at open intake valves... actually most of the time they are fired at closed valves.

[Gelf VXR]

Hi Joe

Yes, tuning injector advance so that it opening during the power stroke when the inlet valve is closed and at its hottest or earlier to ensure enough time for vaporisation well before the inlet valve opens, maybe even more so with overlap and open exhaust valve?

If your injectors are maxed out, you'll still be injecting with the inlet valve open

[5.7ute]

The way I understand it is the reference point is the end of injection, not start. So the end of injection is constant & the start varies.

[Gelf VXR]

I'm trying to understand, I checked the B3702 description as I was referring to LS2 data, but it is the same for LS1


B3702 LS1

"This table will offset the actual opening of the injector referenced to the reference pulses and engine coolant temperature"


B1205 LS2

"This table will offset the actual opening of the injector referenced to engine coolant temperature"

[5.7ute]

There was a thread on the "other" site, where a simulator was hooked up & the reference point was found to be the end of injection, which in a way makes some sort of sense. This would have the fuel charge always firing onto a closed hot inlet valve, giving time to fully vaporise the fuel charge before the intake valve opened. A large duration cam would have the fuel firing into an open intake valve, causing cylinder wall wash, as well as unvaporised fuel entering the combustion chamber.

[Gelf VXR]

There was a thread on the "other" site, where a simulator was hooked up & the reference point was found to be the end of injection, which in a way makes some sort of sense. This would have the fuel charge always firing onto a closed hot inlet valve, giving time to fully vaporise the fuel charge before the intake valve opened. A large duration cam would have the fuel firing into an open intake valve, causing cylinder wall wash, as well as unvaporised fuel entering the combustion chamber.

Can you point me in the direction of the thread?

Think I found it. GenIII EOI fuel timing

[joecar]

Please pm me the link to that thread.

[voda1]

Links:
http://www.hptuners.com/forum/showth...ereencing-what
http://www.hptuners.com/forum/showth...ight=injection
http://www.hptuners.com/forum/showth...njector-Timing