Batch or Multi-Point injection

Hi all

just a quick question. what would be the best to use batch or multi-point injection mode. Running a 4 or 6 engine, having on a 4cly 1/4 and 2/3 together, and on a 6cyl use 1/5/3 6/2/4 ? is there much difference or anything to gain?

What ECU do you have, the terminology "batch" and "multi-point" typically mean the same thing - some sort of non-sequential strategy where the injectors are fired in groups.

In terms of how you pair the injectors up in group fire mode, it is typically not that critical, although in V or boxer engines I would consider spreading the pairs side to side so you don't have for instance all injectors in one rail turning on at the same time.

Do you have a trigger system capable of 720deg sync? Does the ecu have enough injector drives to do sequential?

First, for in-line engines the 4 cylinder would be correct, but for an in-line six cylinder you would pair 1&6, 2&5 and 3&4. Because of different crankshaft throw orders and different cylinder numbering methods (even different year versions of the same engine may have different configurations and firing orders!), you would need to check for flat or V configuration engines which cylinders are at TDC at the same time and pair those.

NOTE, this is not possible with all engines, usually referred to as 'uneven fire', or similar terms, as some will have an ofsett resulting from their design, such as 6 cylinder 90 degree V8 engines.

I would expect, if the ignition is up to it, there is little or no disadvantage in batch firing the ignition - might even have a slight benefit for turbo's if there's a misfire now and again as while the cylinder doesn't make power, there is at least the chance of igniting the charge on the exhaust stroke and so give a little boost to the exhaust gases.

For the injection, there seems to be a few different thoughts, because the fuel injected is halved for each rotation half the fuel is injected into 'dead' air, sometimes even directed to the area around the back of the inlet valve. Some think this is beneficial as it helps chill the air mass and the back of the inlet valve, so there will be less heating of the second discharge into the moving airstream and hence a denser charge is achieved. Some say the evaporation of the fuel displaces oxygen carrying air mass and so is a bad thing. I don't know either way, but I would suggest that first injection stage would be wasteful as much of it may be expected to be carried out the exhaust during the overlap/scavenging by the exhaust.

I would also expect, if getting reasonably close to the full duty (100% open) point of the injectors, the opening and closing delays may become important.

Overall, full sequential would be my choice, the only real advantage of batch is it works directly, and only, from crank angle and it doesn't need a cam/dissy senser to establish if it's on #1 firing or overlap, which is essential for full sequential.

Forgot, there are also some semi-sequential systems which use batch fire ignition with dual output coils, and full sequential ignition.