Auxiliary Control Unit

Timing and Knock Control

 

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.

Normally aspirated

Turbocharged or supercharged

Nitrous Oxide

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

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

 

MSD

JR

J&S

Reprogrammed J&S

Bipes ACU

Programmed retard

Yes

Yes

No

Yes

Yes

Retard based on engine load

Yes

Yes

No

Yes

Yes

Retard based on RPM

No

Yes

Yes

Yes

Yes

Retard based on temperature

No

No

No

No

Yes

Knock sensor

No

No

Yes

Yes

No

Adjustments

None

Retard-to-boost

Knock Sensitivity

Knock Sensitivity
Max retard (4 choices)
10 or 20 on knock

Retard-to-airflow
Retard-to-RPM
Retard-to-temperature

Diagnostic display

None

None

Retard monitor
(optional)

Retard monitor
(optional)

Multi-function (optional)
Retard monitor
Air flow
Air temperature
RPM

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

Display Function

Description

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.

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.

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.

Precision
Tachometer

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.