Especially if your turbo car is driven by other people, a turbo timer is a
great idea. It lets the car idle for a short time after you’ve come to a stop
and switched off the ignition, so cooling down the turbo bearing and preventing
the oil overheating through heat soak. In addition, it also lets the exhaust
manifold - and the rest of the engine - come back down to sane temperatures.
But the trouble with a normal turbo timer is the idle-on time is pre-set. So
whenever you turn off the car, the engine will run for 15 seconds, 30 seconds or
a minute – whatever you have the timer set for. Even if you have only driven
gently around to the shop, the turbo timer will keep the engine running. Sure,
most turbo timers have a cancel switch, but it’s a pain to always have to press
But the Intelligent Turbo Timer is different. Instead of simply always idling
the car for a pre-set period, it actively watches how you are driving in the
kilometres before switch-off. If you’ve been fanging the beegeezus out of the
car, it will idle the car for a longer period, but if you’ve just been driving
gently, it won’t idle the car at all. And it can pick any idle-down time in
It also does all of this automatically – all you need to do is fit the
Intelligent Turbo Timer, set it up for the sensitivity that you want, and then
The Way It Works
In addition to having connections for a heavy current automotive relay to
bridge the ignition key contacts (that’s the way all turbo timers keep the car
running after you’ve switched off), the Intelligent Turbo Timer also has a
signal input. This voltage signal can be from an airflow meter, a MAP sensor or
even the throttle position sensor. (And in cars without engine management, it
can use the input from an added boost pressure switch connected to 12V.) The
only requirement is that this signal input voltage varies with engine load.
Note that the connection of the turbo timer won’t have any affect on the
sensor output – it will continue to work with the engine management system just
as it did previously.
The Turbo Timer watches this voltage signal and when it rises above a certain
level (called the ‘threshold’), it knows the engine is being driven hard. The
Turbo Timer then monitors how long in the 7 minutes before the ignition was
switched off the engine load was higher than the threshold. The idle-on time is
set on this basis.
To tune the application of the Turbo Timer, the voltage level at which the
threshold is adjustable, as is the maximum time the engine can ever idle
Let’s take a look at those two adjustments in more detail.
The threshold is set by a multi-turn pot. The input signal range can be
anything up to ~12V, and can be a signal that rises with load (most common) or
falls with load. (The selection of ‘rising’ of ‘falling’ is made with a link on
the board.) Setting the threshold is easy because a LED on the board lights when
the threshold is exceeded. So setting up this function is just a case of driving
the car and turning the pot until the LED lights when the car is being driven
The maximum idle-on time is set by a rotary switch, which is marked 0-9 and
A-F. Each position corresponds to a maximum idle-on time – for example, position
1 is 30 seconds and position 8 is 4 minutes. Note these are the very longest
times the car can ever idle for – in normal driving, the maximum time is very
seldom reached. The shortest time available is 15 seconds and the longest, 15
The Intelligent Turbo Timer also has a reset switch that can be placed on the
dash. This switch should very seldom be used but it’s included in case the
engine needs to be switched off in an emergency. A LED also lights during the
idle-on time – this can be mounted at the timer or remotely. Finally, there are
also output connections for another relay, which may be needed with some
At its simplest, only four wiring connections are needed to install the
Intelligent Turbo Timer. These are:
- Battery side of the ignition switch
- Ignition side of the ignition switch
- Engine load sensor
It’s easiest to make the ignition switch connections near the switch. Use a
multimeter to locate a wire going to the ignition switch that always has battery
voltage on it. Then turn the ignition key to the ‘ignition’ position and find
another wire that has battery voltage on it only when the key is in this
position. That is, when you turn the switch off, the power on this wire
disappears. Tap into these two cables and connect them to the correct spade
terminals on the Turbo Timer.
The 12V wire on the battery side of the ignition switch always has 12V on it!
This means you should be very careful that this wire cannot contact ground – if
it does, at minimum you will blow a fusible link and at worse, start a fire.
In addition to telling the Turbo Timer whether the ignition key is turned on
or off, these ignition connections also supply +12V to the timer. The earth
connection can be made to any convenient chassis point.
The engine load sensor input can be found by using a multimeter to back-probe
the airflow meter (or MAP sensor, etc) until a wire is located that has a
voltage on it that varies with engine load. Again the wire doesn’t need to be
cut – the Intelligent Turbo Timer engine load sensor wire just T’s into it. This
connection can be made either at the sensor or at the ECU.
Set-up involves turning the multi-position switch to select the maximum
idle-on time you’ll ever want, and then adjusting the sensitivity of the
threshold setting to give the idle-on time that best suits your needs. You
should leave the board accessible for a few days while you fine-tuned the action
of these settings.
Over the years, we’ve often derided turbo timers as a waste of money. However
this one doesn’t cost much and only ever provides the required idle-on time. And
that’s a turbo timer that makes sense...
The Background Story
So how did this kit come about?
The Intelligent Turbo Timer was developed and designed by Silicon Chip
magazine. The kit, along with many others, is covered in the Silicon Chip
publication, High Performance Electronics for Cars. The book is a
must-have for DIY modifiers. The kit for the Intelligent Turbo Timer is available from Jaycar
or through the
The electronics design and development of the Intelligent Turbo Timer was
carried out by electronics engineer John Clarke, while I came up with the
concept and did all the on-car development. (During this period I wore a
different hat to an AutoSpeed contributor, working for Silicon Chip Publications
as a freelance contributor to High Performance Electronics for Cars.)
So by no means should the Intelligent Turbo Timer be seen as an
AutoSpeed-developed project, at the same time I am happy that AutoSpeed endorses
it and promotes it.