Haltech E8 - Manual (Page 36)

Haltech E11/E8 Instruction Manual
Tooth Offset and Trigger Angle Relationship
Tooth offset and trigger angle are closely related and are best explained visually so see below for a visual
representation off the tooth offset.
The tooth offset is the number of teeth between the home event and the tooth that is chosen to be the
trigger tooth. In the example above the home event is the missing tooth.
The trigger angle is the angle between the trigger tooth and TDC therefore the tooth offset plus the trigger
angle equals the angle between the home event and TDC.
As can be seen above the trigger angle is simply the angle before top dead centre (TDC) at which the
trigger event occurs (when the tooth selected to be the trigger tooth passes by the sensor). In the case of
a multi tooth trigger without a missing tooth (such as a Toyota 24 trigger) the home home event comes
from a separate single tooth sensor usually located on the camshaft.
When using a custom trigger of any sort the sensor must produce at least one trigger event for each
ignition event and each trigger must occur a constant angle BTDC (in other words the teeth must all be
evenly spaced and the number of teeth an even multiple of the number of cylinders the engine has).
The trigger angle value must be greater than the maximum advance you wish to run, so if the maximum
advance you wish to run is 40 deg, the Trigger Angle value needs to be at least 40 deg (its wise to have at
least 10 degrees margin). If the Trigger Angle value is set too low, the ignition timing will not be able to
achieve the full advance set in the ignition map/s.
By selecting the correct trigger tooth in the tooth offset field this should always be possible.
Setting the tooth offset and trigger angle on an engine where the location of the crankshaft position sensor
and camshaft position sensor is unknown is very easy and requires only a timing light. The following
procedures outlines how to achieve this:
Go to the fuel setup page and disable the fuel injectors (at this stage it is not desired that the engine
attempts to start), to reduce stress on started motor it is also advisable to remove the spark plugs to help
the engine crank more freely when setting base timing (be careful when doing this as spark from ignition
coils have been known to cause severe injury and even death on some occasions).
Page: 36 Copyright © Haltech 2008
Figure 30: Trigger Angle and Tooth Offset Visually Outlined