AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 98)

Page 98 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
Part 3
– Tuning Guide
Background
What is “Tuning”? Tuning can mean anything from adjusting the idle mixture screw on your
carburetor to experimenting with custom length headers for your engine to setting up the flow
ratio between primary and secondary injectors for your EFI calibration. Tuning covers a wide
range of topics and not all are related to fuel injection. For the purpose of this manual, tuning
refers to the act of making changes to a calibration file for an AEM engine management system
(EMS) to optimize the performance of an engine.
In its most basic form, EFI tuning involves optimizing the fuel flow and spark advance variables
to maximize performance and economy.
Fuel Tuning General
Concepts
The chart at left illustrates the
effect of fuel flow on engine
performance at a constant
operating set point (fixed RPM
and throttle position). This kind
of data is recorded under
laboratory engine testing
conditions. The test is started at
a very rich air/fuel ratio. The
mixture is leaned at a controlled
rate and data is recorded along
the way. The first transition
occurs when horsepower
reaches a peak and begins to fall
again (best power AFR). The
next transition is when cylinder
head temperature reaches a
peak and begins to fall. The
next item of interest is peak
exhaust gas temperature (EGT).
Shortly afterwards, the specific
fuel consumption reaches a
minimum and begins to increase
(best economy range) indicating
the engine is running at a
mixture that is so lean, it is
becoming difficult to support
combustion.