For 5 cylinder and odd-fire V6 engines the crank trigger is not enough. The ECM must know which cylinder (which sparkplug, which transformer, which IGBT) to fire
GenBoard/VerThree has input for cam-trigger (secondary trigger) and enough outputs to drive an 8 cylinder fully DIS setup.
Beware - think twice if you really want to depend on camsync
For even-fire engines wasted-spark can be a better (and certainly simpler) approach. It is simpler to configure the ECM for wasted-spark, since cam trigger is not needed (so less things to break). Wasted spark wastes very small amount of energy, only about 8..10% for real wasted spark, when the same transformer fires 2 cylinders' sparkplugs, since the voltage will be smaller on the exhaust stroke cylinder while current is essentially the same.
For trendy COP (coil-on-plug) installations, cheating wasted spark really wastes some energy, because the exhaust stroke cylinder's sparkplug is also energized fully.
There are, however a number of reasons for using camsync. First of all with high horsepower small displacement engines it can be very difficult to get a stoich idle with large injectors. A non-synchronised trigger means wasted spark and phased injection. Every injector fires twice for each combustion event. Since injectors have a minimum reliable opening time this can cause a problem.
This also excludes the possibility of adjusting fuel trims on a per-cylinder basis. On many engines this can be very important. Especially Subaru engines where the extra heat in the cylinder next to the turbo makes it a detonation target.
Per-cylinder knock sensing also requires camsync as the ECU would otherwise have no way of knowing which cylinder was knocking.
What are the requirements for fully DIS ignition setup?
The camsync must be between given 2 cyls' spark event! In other words, if the camsync pulse is overlapped by the used ignition advance range of a cylinder, it's currently not supported. For a 4 cyl, this means that if ignition advance is set to 8..45 degree BTDC, than the chosen camsync trigger pulse (the edge that is configured to trigger the processor) must be outside of that 37 crankdegree window (out of 180 crankdegrees) plus some safety margin.
This is not a hardware limitation, just a firmware shortcoming, that's planned to be improved anyway (just noone asked for it yet).
Anyway, for a dual trigger setup make sure you plan cautiosly, and document your progress in wiki so others can warn you should anything be done differently.
Only cam, no crank trigger - cu
Above we assumed that besides the cam trigger there is always a crank-trigger (the crank is the preferred source for timing as the cambelt usually causes a few degree sloppiness). However a cam itself also enables us to run an engine.
- Note that during 720 crankdegree revolution (if the common 1-tooth camtrigger is used) the RPM can change significantly. This is not supported.
- multitooth cam signal is possible: allow running the engine so max time between synchron teeth is only say 20 crankdegrees. This is supported, but you have to connect the cam-trigger to the primary trigger input, and pretend that it's crank. Just think about it, works like a charm: set an 8 cyl for fully DIS (say COP) as it was an 16 cyl wasted spark system.
- a tricky cam signal-train would help faster startup at cranking too (not yet supported)
- when there are both crank and cam triggers, but crank is lost: this limphome functionality (optionally with somewhat retarded spark) is needed very rarely, so planned for later (2005 March..May).
See also: GenBoard/Manual/InputTrigger
Go back: GenBoard/Manual