7.3 Ignition Settings 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
• Distributor type pickup, such as HEI, TFI, or EDIS (although the last is not a distributor, the MS3Pro will see
a similar signal.). Noise filtering is often useful here. A typical setting would be crank tach period masking
with 1ms and 30%.
• Wheel decoder and other more advanced installs. Noise filtering may be useful on some installs. Due
to the multi-toothed input signal the rejection time periods need to be set far smaller. e.g. on a V8 with
distributor at 6000rpm, the time between tach pulses is 5ms. A 36-1 wheel on the same engine gives a pulse
every 0.6ms (600us). Using too large a filter time will filter out the real signal.
7.3.7 Knock sensor settings
Note: While this is a fairly good setup as far as knock sensing goes in a race ECU, getting OEM like levels
of knock protection generally requires grenading a few motors on the dyno to get it dialed in perfectly.
Knock sensing can provide an extra layer of protection, but never use knock sensing as your only spark
tuning tool!
Spark knock is the sound of abnormal combustion in an engine. Once combustion in a spark-ignition internal
combustion engine is initiated by a spark, the flame front is designed to spread from the spark plug and travel
across the combustion chamber rapidly and smoothly. As the flame front propagates across the chamber, the
remaining unburnt air-fuel mixture can ignite spontaneously (auto-ignites) before the flame front arrives, due to the
increasing pressure and temperature in the combustion chamber. When this occurs, there is a sudden jump in the
pressure in the cylinder. This causes in the characteristic knocking or pinging sound. It is most common at low-mid
rpm and high load, such as ascending a hill in too high a gear.
Prolonged heavy knock is likely to cause severe and permanent engine damage and must be avoided.
It is a common misconception that engines make most torque just before knock. In reality, there isn’t much of a
connection between the knock threshold and the timing that makes best torque. A knock resistant engine may start
losing power well before the onset of knock, while a knock limited engine may have the point where it makes best
power past the knock threshold (and not safe to reach without higher octane fuel). Ideally, set timing on a dyno to
achieve maximum brake torque (MBT) timing. Even with a well tuned engine, factors such as fuel octane, intake
air temperature, coolant temperature, engine age and condition, air/fuel ratios, air density, altitude and humidity
and others can push the engine from a safe condition to borderline knock or worse. The knock control system is a
safety measure designed to retard timing under these conditions and safeguard the engine.
The MS3Pro contains an internal module that can process one or two knock sensors. It also allows input from
an external module that gives an on/off, “knock” or “no knock” signal. The knock sensor inputs use dedicated wires
intended for connecting directly to a knock sensor. External modules would use the digital input wires instead.
There are two main types of knock sensor: Resonant and wideband sensors. The resonant sensor is tuned to
a particular frequency and is only likely to work on an engine with a very similar bore size. (Bore size determines
"ping" frequency.) The wideband sensors give a lower voltage output but operate over a wider frequency range,
and can usually be applied to different engines.
The GM resonant knock sensor pictured above is tuned to a specify frequency, like a tuning fork. When this
frequency is applied to the sensor (through its connection to the engine), a piezoelectric crystal inside the sensor
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 171
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