This article is very brief and just
covers the timing of injector outputs on port injection
engines. It does not cover direct injection systems. Injector timing on the Modular ECUs can be mapped
against RPM and load, and the number represents the end of the
injection pulse in degrees BTDC.
Injector Timing Table
On a staged injection engine, you can set the
injection timing separately for each stage, to promote better
mixing, minimise water hammer in the fuel rails and so–on.
Number of injection stages can be found under “Injector
Staging”
Injection timing can be set separately
In terms of appropriate values for injection timing,
there are a few possible ways to do it, and to some extent it
depends on what you’re trying to optimise. One technique I’ve seen people do is to adjust the
injection timing until the indicate air-fuel ratio is richest
(given constant fuel delivery), indicating that the combustion
is most complete (least air left over). I don’t know if
corresponds to any other real world effects such as minimum
emissions or maximum torque, both sound reasonable but I won’t
believe it until I see some data. A common technique is to do what they call closed
valve injection, where the end of the injection pulse happens
before the intake valve opens. This requires a value of about
380° or higher. For the off-idle throttle response,
injection timing can make a big difference and I’ve found
values like 380 work fairly well. Throughout medium to high RPM and on load, injection
timing can have an impact on torque, depending on the engine.
On a production engine it makes less of a difference than on a
high overlap engine in my experience. Another use for adjusting injection timing is to
minimise HC emissions. On a large-overlap engine, for example
an engine with big cams, often emissions will be lower by
injecting the fuel after the exhaust valve has closed. This
means that no fuel can “short circuit” the engine under open
throttle conditions. In tuning cars for emissions I’ve found
this makes a big difference, but you’ll need a 4 or 5 gas
analyser to see it. Rotaries I’ve found like values around 180 degrees
to have decent off-idle response, and side-port engines don’t
seem very sensitive to injection timing. Naturally aspirated
peripheral intake port engines are a different story however. Finally, as I mentioned before you can set the
timing differently on different stages if you want to. When I
tried this on my 13B turbo before she went to a better place,
I didn’t find it made any difference to torque at all, but one
tuner has told me it does so the option is there in case you
need it. At the very least you can ensure that you don’t have
multiple stages with the same end of injection angle adding to
the water hammer effect of the injectors closing. Thank you.