HKS Speed Limit Defencer (SLD)
In this feature, Temple of VTEC - World's own comments are published in italic fonts.
HKS is one of the premier Honda tuners in Japan. The Malaysian HKS
representative is Aerotech and is run by Mr Rennie Khoo, a very
knowledgeable engine tuner in Malaysia. Recently, I've had the very good
fortune of receiving Rennie's hospitality and we are now embarking on a
special feature of tuning products that HKS specially makes for Honda.
Drop by often to look out for new products covered. To contact Aerotech in
Malaysia, their phone number is 60-3-7556112.
All JDM Honda models have an artificial 180kph top-speed limit. This
limit, existing even on the NSX Type-S, is implemented by Honda via the engine
ECU. The following explanation of how the 180kph limit is implemented is by kind
courtesy of Rennie.
The Vehicle Speed Sensor (VSS) is a device attached to the transmission that
measures the car's speed via tracking the number of revolutions of the wheels.
The output of a VSS is in either sine wave, square wave or in the form of pulse
counts. When the engine ECU detects the car is travelling at 180kph via the VSS
signal, it reacts in one of two ways. It will either stop 2 or more injectors or
it can cut the ignition (probably intermittently). This reduces engine power
output drastically, slowing down the car until its speed drops below 180kph.
According to Rennie, in JDM cars, cutting off the VSS signal to the engine
ECU can lead to one of three conditions. One is the ECU will just ignore the
absence of the VSS signal and continue operating as normal. In another, the
engine simply won't start or will die when gear is engaged. The final condition
is the ECU program, because it now cannot determine how fast the car is
travelling, goes into a backup safe mode in which it runs the engine
rich. This unnatural rich mode is undesirable and will actually lead to a slight
loss in engine power as well as oil dilution (contamination of engine oil with
In Hondas, loss of the VSS signal will cause the ECU program to go into the
backup safe mode. In addition, it will invoke a trouble code of 17 (for EF8/EF9
CRX/Civic SiR) indicating 'faulty vehicle speed sensor'. In
the HPL archives, Doug MacMillion said that cutting off the VSS signal will also
stop the ECU from engaging the high cam lobes for the B16A.
The HKS Speed Limit Defencer (SLD) device works by intercepting the VSS
signal and substituting its own signal to the ECU. This device has four wires,
two of them for power and ground and of the other two, one receives the VSS
signal and the other feeds a substitute signal into the ECU.
When the SLD device detects that the VSS signal is indicating that the car is
travelling at 180kph, it substitutes a signal to the ECU indicating a lower
speed. Because the VSS signal is not a major parameter used by the engine ECU to
control engine operation, this method effectively bypasses the artificial 180kph
top speed limit in the best manner.
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