Fuel injection firing questions, side to side or all 4 or ????? Options

[Mueller]

currently for my Megasquirt install, i have it wired up so that the fuel injectors are wired with 1 and 3 are on same circut and that 2 and 4 are on the same circut.


if i read it correctly, D-Jet fires 2 injectors every ignition event...the L-Jet fires all 4 injectors every ignition event

has anyone fooled around with the fuel injection to see which method works better????

[lapuwali]

Frankly, I doubt you'd even notice a difference. L-Jet went to "all one batch" fire after it was shown that doing that made no real difference over the paired batches D-Jet does. All sequential (injector firing timed to each cylinder) also has very little effect above idle or light cruise loads. So, L-Jet went for the simplest approach, since doing that didn't change a thing until emissions requirements at idle got so stringent that even the small difference full sequential makes became significant.

The primary reason this is so is the duty cycle of the injectors. At peak loads, the injectors are typically open 70-80% of the time or more just delivering enough fuel. If they're only closed 20-30% of the time, and the intake valves are only open about 30-40% of the time, there's not much point in worrying when the fuel is injected relative to the intake valve events, since nearly half of the fuel will be sprayed at a closed valve no matter how you time it.

[airsix]

Check out the atricle on the SDS site about this. They tested batch vs. sequential and it amounts to very little difference. Some small difference at idle and extremely low load. No difference when there is moderate to high load.

-Ben M.

[ArtechnikA]

there's a long complicated ceremony for timing the MFI adjustment pump to the firing cycle of the engine. all the reports from people who've had to replace a broken belt in the boonies or in a hurry during a race report that even with sequential timed direct-port injection that it produces no discernable difference. it probably shows up on a well-calibrated dyno at some throttle-opening, load,.and rpm regions or Porsche wouldn't have the procedure... but the real world data says it's not worth losing sleep over...

[TimT]

All sequential (injector firing timed to each cylinder) also has very little effect above idle or light cruise loads.

bingo

sequential is mostly for fuel economy/emissions..


I wired my 911 injectors "batch" fired, it made a cleaner installation than if I wired them sequential, also eliminated me having to machine my cams for a cam position sensor

[lapuwali]

The interesting thing is the MFI is capable of delivering 100% of the required fuel even at WOT during the time the intake valve is open, simply because the system pressure is so high. I don't remember the numbers for MFI, but for SPICA, a very similar system used on Alfas, the system pressure is something like 50 bar (700psi or so), which is why SPICA systems have hard lines to the injectors from the injection pump. Genuine full sequential operation is actually possible with these systems. If the injection pumps were controlled by modern digital electronics instead of the mechanical systems they used, MFI would theoretically be capable of much finer fuel control than current gasoline EFI systems.

Current "common rail" systems for diesel engines use a setup similar to gasoline EFI, except the rail pressures are way above the 3-4 bar used by gasoline systems (something like 1200 bar or so, HUGE numbers), meaning all of the injection could take place in sub-millisecond times, so it would only take a few crank degrees even at very high engine speeds. Such systems may eventually be applied to production cars, though they'll proabably be usurped by gasoline direct injection instead, which will have big benefits in economy and emissions, with no power losses. Turning the clock right back to the mid-1930s, when Bosch was injecting gasoline (well, gasoline-like) fuels directly into the cylinders in Daimler-Benz aero engines (and postwar, into 300SLR engines). Nothing new under the sun, really.

[Mark Henry]

Check out the atricle on the SDS site about this. They tested batch vs. sequential and it amounts to very little difference. Some small difference at idle and extremely low load. No difference when there is moderate to high load.

-Ben M.

ayep

SDS is batch fired, hook them up any way you like. Works gUUd

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