AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 258)

Page 258 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
Alt Function Output
Units: User Defined Output Description: If the Alternate function is activated, this output channel
will be activated also. Can be used to drive an LED, injector, etc.
Alt Function Input
Units: User Defined InputDescription: Input switch that triggers the alternate function.
Channels (can be viewed or logged)
ALT
Units: On/Off Description: Displays the current status of the alternate function.
Fuel Trim (Alt)
Units: uS Description: Displays the fuel pulsewidth from the Alt Fuel Trim correction.
Tuning Drag Race Anti-lag
The basic idea is to fire the ignition after TDC to cause afterburn in the exhaust to spool the
turbocharger to a desired boost level for launching the vehicle. There are a couple of things to
consider to obtain the desired results.
Engine Speed: The amount of engine speed is directly related to how much boost can be made
under anti-lag conditions. A higher engine speed will equate to a higher boost level as well as a
faster boost response. If you are unable to make the desired boost pressure for launching, no
matter how much ignition retard is used, then more than likely you need to increase the Alt On
Above RPM.
Ignition Retard: The more the ignition is retarded, the more afterburn and heat will be put into
the exhaust. Start at a conservative -10 degrees, and add more ignition retard until the desired
time and boost is reached. Typical numbers are between 15 and -20 degrees of ignition. Either
the Alt Spark Fixed or the Alt Spark Trim can be used for retarding the ignition.
Engine Load: If the boost control is set at "x" pressure, then no more "x" pressure can be
obtained when launching. The option Alt Overboost, however, will allow a lower launch boost
than the operating boost setting, by turning OFF the alternate function when the engine load has
surpassed the option.
Additional Fuel: Added fuel will also aid in the anti-lag process by insuring the fuel mixture will
be there throughout the engine cycle. A typical value for Alt Fuel Trim is 5-10%