This article explains the different load
axes of ignition mapping, as well as temperature corrections
for ignition timing. Similarly to the fuel mapping, the Adaptronic
Modular ECUs can use a combination of MAP and TPS for ignition
timing tuning. The ideal measurement would be the pressure of
the air in the cylinder, which would be best approximated by
MAP x VE. However we wouldn’t want a system whereby someone
changes the fuel map and then that changes the ignition timing
as well – even though that might be scientifically accurate,
it’s important for ECUs to behave as tuners expect them,
otherwise the tuner can’t make the ECU do what is needed. It’s set in the settings for your ignition map, so
if you’re using dual maps there will be a setting for ignition
map 1 and another for ignition map 2.
Tuning-Ignition > Tuning Modes then enable dual maps
Notice that the ignition maps can be set separately.
The most basic is MAP. This has a pretty good
correlation with the pressure of the air that’s in the
cylinder, and therefore how quickly the flame front spreads
through the engine, which is what you need to compensate for
when you tune ignition timing against load. So this is the one
we recommend most of the time.
Changing “Operator” can be found in “Ignition Map Settings”
page
If you don’t have a MAP measurement, then you will
have to use throttle position instead. This does not correlate
all that well with pressure in the cylinder; at low RPM
especially there will be a lot of movement within the first
20% of throttle change and from then on it won’t change much
at all. So tuning ignition on throttle position will take
longer than on manifold pressure but on some engines that all
that is available. Although pressure ratio is perfect for tuning fuel,
it’s not appropriate for ignition timing – if it’s not obvious
why then I’ll leave that as an exercise for you to work out. We also offer MGP as a measurement. I don’t
personally think it’s a good idea, because it’s a absolute
pressure that affects the flame propogation rate, not the
pressure relative to the outside of the engine. The rapid
spreading of the Apollo 1 fire and a similar event in the USSR
was due partially to the pure oxygen environment but also the
elevated pressure; they had the command module pressured to
about 1.1 bar or 16 PSI of absolute pressure during the Apollo
1 fire when the flammability testing was all designed to
operate in space with a pressure of about 0.3 bar or 5 PSI.
But I’ve heard the argument from one person that “tuners are
used to tuning off gauge pressure” so we’ve put in that option
as well. On turbocharged cars with individual throttles,
often the MAP does not fully tell the story of how well the
engine is breathing, and that’s why those car need to have a
combined MAP x TPS tune for the fuel model. On those cars,
it’s possible to improve drivability by selecting a MAP + TPS
ignition tune, perform the full MAP tune while leaving the TPS
map at zero, and then adding some positive values in the TPS
map at light throttle to increase light throttle torque. I can’t think of a reason why someone would want to
multiply MAP and TPS maps, as on the fuel system, but this
option is also there for anyone who wants to use it – and
these can be either MAP or MGP (although as I said above, MGP
doesn’t really represent anything on the car). In addition to the basic ignition tuning modes, you
can, if you want to, add in correction for air and coolant
temperature. Normally the engine would be tuned with these at
zero, and then safety functions can be added for example
putting in some negative values at high air or coolant
temperatures. Please do not tune the engine with negative
values in these tables, because what can happen is that during
tuning, while the engine is on the dyno and there’s a lot of
heat soak, temperatures are high and you can be in the part of
the map with the negative correction in it. So if you tune
with this correction in place, your basic map may end up too
far advanced, and then when Fred takes it out for a drive when
it’s cold the ignition timing could be too aggressive. Setting up closed loop ignition timing with
reference to knock control will be a separate article. Thank you very much!