AEM 30-71XX Infinity Stand-Alone Programmable Engine Mangement System Full Manual - Manual (Page 208)

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© 2014 AEM Performance Electronics
Infinity User Manual
Launch Antilag
Turbo lag is defined as the time delay before the turbocharger has produced boost pressure.
Anti-lag is when a turbocharger is subjected to a very late burn causing the exhaust to expand in
the turbine housing. This energy is concentrated at the turbocharger causing a very quick turbo
spool up. Since turbochargers are designed and sized to operate at specific rpm ranges and air
flow conditions, some turbo lag is inherent in the system. To fully understand turbo lag, you must
first understand the operation principles behind what causes a turbo to make boost.
Boost is not made by RPM alone. There is a big difference in the airflow through an engine at
6,000 rpm in neutral, 6,000 rpm in first gear at part throttle, and 6,000 rpm in high gear at full
throttle. Turbochargers are even more effected by these airflow differences and especially load
differences than most other devices. This is why you may be able to see a small amount of boost
with a positive displacement supercharger at WOT in neutral, but you may not see any boost at
WOT in neutral with a turbocharger.
A given turbocharged vehicle may produce full boost in first gear by 3,500 rpm. This same
vehicle may produce full boost in 4th gear by 2,300 rpm. When pulling a heavy trailer, it may
produce full boost by 1,800 rpm even in 1st gear. These conditions are more specific to manual
transmission vehicles as the boost has to build in each gear after the throttle is closed during the
shift. Automatic transmission vehicles operate differently as they can be "loaded" by stalling up
the converter and placing enough load to build boost before the vehicle even moves. Also, with
an automatic transmission, the throttle is not shut during shifts which causes the boost to "pop
up" because the turbo is supplying enough air flow to feed the boosted engine at high rpms and
suddenly the rpms are drastically cut down by the shift as well as increased load has been
placed on the system at the same time. This can cause an engine that is accelerating in 1st gear
with low boost to instantly go to full boost upon shifting into 2nd gear.
Tuning 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 engine speed limiter.
Ignition Retard: The more the ignition is retarded, the more afterburn and heat will be put
into the exhaust. Start at a conservative 5 degrees ATDC, and add more ignition retard
until the desired time and boost is reached. Typical numbers are 15-20 degrees ATDC
of ignition retard.
Engine Load: If the boost control is set at "x" pressure, then no more "x" pressure can
be obtained when launching. The Infinity Tuner can allow a lower or higher launch boost
than the operating boost setting.
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 increase is 5-10%.