Auxiliary Control Unit
Timing and
Knock Control
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ACU with Display |
2.6" W x 4.25" L x 0.875" H
Timing control for '90-'97 Miatas
The
Bipes ACU (Auxiliary Control Unit) dynamically retards the timing of your
engine to protect it from detonation or knock.
The unit works on either normally aspirated or forced air (turbocharged
or supercharged) engines.
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Normally aspirated |
Turbocharged or supercharged |
Nitrous Oxide |
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Probably the easiest and most inexpensive power
modification to the Miata engine is to advance the base timing. This technique
is well known and documented. A problem can arise if you advance the timing
more than a few degrees: detonation. The ACU allows you to enjoy the power
gains that advanced timing offers while protecting your engine from
detonation or knock. |
If you followed supercharger installation
instructions and set the base ignition timing back, you helped protect your
engine from detonation but you robbed it of power. Changing the base timing
affects timing under all conditions, not just the conditions at which your
engine is susceptible to knock. The ACU retards timing only when needed. |
To protect your engine, you may need to retard
timing when you switch on your nitrous oxide. The ACU can be configured to
automatically add a user-selectable amount of retard when the nitrous is
engaged. |
ACU Features
- 3-input timing map: RPM, airflow (boost), and air temperature.
- Retards up to 20 degrees of timing.
- User programmable.
- Easy to program.
- Self-contained - no PC, keypad, or other additional device required to program.
- Integrated diagnostic display. Click here for display details.
- Precision tachometer display mode.
- Software upgradable by replacing a chip.
- Best value (most features, low cost).
Bipes ACU Exclusive Feature
The Bipes ACU is the only add-on timing device to offer timing control mapped to intake air temperature.
The Link, a replacement ECU priced at over $1000, offers the option of air temperature mapping. This Link option requires the addition of a special temperature sensor that costs another $100! The Bipes ACU uses the Miata's own temperature sensor to provide air temperature mapping at no extra cost.
Compare for
yourself
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MSD |
JR |
J&S |
Reprogrammed J&S |
Bipes ACU |
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Programmed retard |
Yes |
Yes |
No |
Yes |
Yes |
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Retard based on engine
load |
Yes |
Yes |
No |
Yes |
Yes |
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Retard based on RPM |
No |
Yes |
Yes |
Yes |
Yes |
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Retard based on
temperature |
No |
No |
No |
No |
Yes |
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Knock sensor |
No |
No |
Yes |
Yes |
No |
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Adjustments |
None |
Retard-to-boost |
Knock Sensitivity |
Knock Sensitivity |
Retard-to-airflow |
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Diagnostic display |
None |
None |
Retard monitor |
Retard monitor |
Multi-function (optional) |
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Price |
$150 |
$400 |
$435 - $595 |
$435 - $595 |
$209 |
MSD is the Sebring Supercharger Mazda Miata
Boost Control by MSD Ignition, available from several sources.
JR is the Jackson
Racing Boost Timing Control Unit from Moss Motors
J&S is the
Safeguard unit by J&S Electronics, available from several sources.
Programmed J&S is
the Safeguard unit with Miata reprogramming by the manufacturer.
Display Details
Sample
display: Precision Tachometer mode
The display can be configured to display any
one of four functions. Display choices are selected via the switches at the
back of the ACU (click on the
Programming section at the left for details).
Display
Options
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Display Function |
Description |
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Retard |
Displays the amount of
timing retard that ACU is applying. Each LED = 2 degrees of timing retard. Probably the most useful display mode. It
permits verification of the RPM set points, the airflow map, and the
temperature map. It also allows confirmation of the maximum retard
selections. |
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Airflow |
Displays the amount of
intake airflow. No LEDs on indicates no airflow; all LEDs on indicates
maximum airflow. It is normal for several LEDs to remain on while the engine
is running, even at idle. Useful to verify that the ACU airflow
connection has been properly made. |
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Air Temperature |
Displays the intake air
temperature. No LEDs on = 0 degrees F. Each LED = 20 degrees F. Useful to verify that the ACU air
temperature connection has been properly made. Also useful to monitor intake
air temperature. If you do not have cold air induction, monitoring this
display may just convince you to make that your next project. |
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Precision |
Displays RPM. Each LED =
100 RPM (above 500). No LEDs on means RPM is 500 RPM or less. One LED on =
600 RPM, 2 LEDs on = 700 RPM, etc. Permits accurate adjustment of idle speed. |
Note
The display will not be updated while the
engine is not running, and is not meaningful while the engine is not running.