Ignition retard at boost wanted
The new programmable electronic ignition system from the March,
April & May 2007 issues is very interesting but I am trying to figure out if
this will suit my car.
I am after something to retard timing by 3° per PSI of boost on
my 650HP supercharged Chevrolet engine (max boost 6 PSI) in order to be able to
run advanced timing for better fuel economy when not in boost. Can this be done?
(J. A., Silverdale, NSW).
There are several
ways of switching in retard on turbo boost. The first is to just include this in
the mapping of timing against RPM and pressure (load). So at high boost, the
retard is increased. This can be done because the MAP sensor will measure the
boost pressure and this will be in the high load map sites.
Another way is to include extra retard in the second ignition
timing map and then switch this map when required. So map alpha would have your
normal timing and map beta would have the boost retard. You could map the entire
RPM/load sites for the boost. Note that the boost retard can be altered for the
boost pressure using the MAP sensor signal.
Alternatively, you can use the knock sensor input. This would
be a little harder to do as the input needs to see a voltage from 1.25V to 5V in
order to change the retard value. So a voltage that varies with boost pressure
could be applied to the knock input when the retard is required.
The actual retard value will depend on the 0.5° or 1°
resolution setting and the voltage applied. The retard amount can be seen on the
display. See the April 2007 issue for the knock sensor article for more detail
on this input.
