ECUTEK - Original verses Aftermarket ECU

This is a comparison of the pros and cons of the various ECU options available to someone with a 1999 or 2000 model year Impreza.

Feature	Product
Feature	Original ECU	Possum Link ECU	DasTek (APS) Unichip
Appearance
ECU Type	Complete ECU	Complete ECU	PiggyBack ECU
Fitting	Plug and play. Change in 3 minutes.	Plug and play. Change in 3 minutes	Requires cutting of loom wiring.
Appearance	ECU fits car as standard. No signs of modification.	Replacement unit - different in appearance.	Additional cigarette packet sized unit
Reprogrammable	Yes. Initially by dealer only. Soon by owners.	Yes. With Link handset or laptop software by dealer or owner.	Yes. By Unichip Dealer Only.
Compatibility with Subaru Diagnostic Tools	Full compatibility and accuracy	Not Compatible	Compatible, though diagnostic tools will read inaccurate values from the ECU, since the piggyback module modifies the I/O signals of the ECU.
Reports diagnostic trouble codes when engine parameters go out of safe limits	Yes	No	Yes
Mapping effort required to get good idle, cold start & aircon function	None - ECU does this as standard. Only modify what is required.	ECU must be programmed fully. Provided with a map that should get the car started within 30 minutes.	None - Piggyback only modifies what is required, leaving what is already ok intact.
Air Flow Metering Method	Mass Air Flow	Manifold Pressure	Mass Air Flow
Closed Loop Lambda Control	Yes	Yes	Yes
Closed Loop Knock Correction	Yes	Link Plus only	Yes
Charcoal Cannister Purge Control (Emissions)	Yes	Link Plus only	Yes
Air-con aware Idle Control	Yes	Link Plus only	Yes
Fuel and Ignition Map Resolution (RPM x Load)	16x16 (256 zones)	16x6 (96 zones)	17x12 (204 zones)
Load Scaling Maps	Yes	No	No
RPM Scaling Maps	Yes	No - Fixed 500 RPM intervals	No - Fixed 500 RPM intervals
Boost Control	Yes. Closed loop control.	Yes.	Optional Extra
Boost Map Resolution	8x8 (64 zones)	16x1 (16 zones)
Wastegate Map Resolution	8x8 (64 zones)	3 values - base, sensitivity and activation RPM. See link docs.
Rev Limit Adjustment	Yes	Yes	No
Soft (Smooth) Rev Limiting	Yes	Yes	Yes

This comparison is quite technical in nature. If terms are used with which you are not familiar, please check the tuning section of the site for further information and explanation. If you still need more info, please mail us, and we'll do our best to make things clearer.

This aim of this article is intended to be an objective and fair comparison of products. If you feel there are any omissions or errors in the above comparison, please report them to us for correction of this article.

UNICHIP
Effectively the Dastek Unichip only tunes off TPS , there is nothing there for tune on AFM, so what this does is not make compensations for the increase in air mass from a colder day, so the ECU sees more air flow and thus makes it rich, hot days it sees hot air been less mass and therefore less air flow and without correction runs learn, as you know without a temps sensor it makes it very hard for a constant tune only using TPS as the volumetric efficiency changes, reason why Unichip recommends they only tune to 11:1 .

Not really a problem on a STi as it has a temp sensor, but the WRX has been seen go from low 10's to high 12's (Air/Fuel) on extremes.

LINK
The current plugin LINK does not offer the ability to change Camshaft timing

Original verses Aftermarket ECUs