Improving the cars performance is not about fitting an ECU and driving away. It is about correctly mapping all the engine parameters across all throttle positions and across the entire rev range. Knowing how to do this takes years of experience and is not something picked up in an afternoon. Most ECUs do fundamentally the same thing. That is, allow a tuner to remap the air/fuel ratios, the ignition timing and the boost levels to improve performance. All three of these maps work in conjunction with one another and changing one will effect the others.  

Too often, we can get caught up with how much power a particular ECU can deliver at the wheels. Any ECU can give huge power gains with a lean enough air/fuel mixture and high enough boost levels. Just don’t expect your engine to last long. Given the variability involved with dynos too, comparing power figures from shop to shop and car to car is simply meaningless. You simply can’t compare figures unless you have a proper base line to work from to begin with.  

Also important to note is that the "rush" you feel when accelerating hard, is the torque your car is producing and has nothing to do with the power. The more torque your car can pump out, the more your cheeks smear when mashing the go pedal. 

Finally, there is a misconception too that a piggyback ECU system is not as good as a full replacement ECU. Having now leant about and spent time with both, I would strongly argue the other way. I can't see how a full replacement system will produce any better result than a piggyback one. In fact, the basic operations are best left to the factory ECU. Subaru will have spent countless hours and millions of dollars designing and developing functions such as cold start operation, air temperature compensation and knock sensor retardation. Changing them can upset the car significantly resulting in a rough idle or jerky throttle. Why redesign them if they work perfectly to begin with. Full replacement systems may allow more sensor inputs and other parameters to be worked on but these are really only desirable if you run a full blown race car. Not for a daily driver such as most would use the WRX.  

So now we come to the ECUs……… 

Possum Link  
It is quite clear the Link ECU was set up for maximum power and as a result, the driveability and reliability were sacrificed. The Link uses an aggressive air/fuel ratio above 12:1 high in the rev range. This is leaner than was recommended by any other tuner I spoke to. Running lean is great for power gains (and fuel economy) but not for engine longevity. The big rush of power that kicked in at 3500rpm felt great but keep in mind, this urge is only felt as a result of the lower than normal power up until this point. The lower the power down low, the bigger the rush felt up high. 

The poor driveability of the Link can be attributed to the fact it only has 96 mappable zones (compared to over 200 for the other ECUs tested here). Less zones means less control. The Link manual states it has "32,000 interpolation zones. Every ECU interpolates between its mappable zones and the more it has to interpolate, the less control you have over it.  

There is no doubt the Link is popular, both in the UK and Australia. Good marketing and the link to Possum Bourne (excuse the pun) probably has a lot to do this. The Link does provide many tools for performance shops and self-tuners to play with the car. These tools allow the driver to set the car up with great precision (at a much greater cost of course).  

Look, the Link is not a bad ECU. I just don't believe it deserves the hype it gets having now compared it to some opposition. In the right tuning hands and with a few more hours, I'm sure it could match the others here but unfortunately for this article, it limps into 3^rd place. 

Microtech (BGT ECU) 
It is difficult for me to comment on the Microtech as I did not test it personally. I did chat to Vin about the system and spoke at length with Michael Fisher about it so at least can summarise a few key points. 

Overall, the Microtech did an excellent job. It matched the Unichip for peak power and was only a smidge behind in torque. It was really neck and neck above 4000rpm. Below this, the Microtech does lose ground but it's still quite close.  

On the road, the Microtech showed good acceleration and was once again only just behind the Unichip for pace. I would have loved to run in-gear acceleration to compare the two but we decided at the start not to do this for logistical reasons. Something I regret in hindsight as it would have really shown up any part throttle differences between the two.  

The Microtech offers a host of features and BGT have the tuning experience to get the most from it. The customer service was also very good. I have also personally found Vin to be very approachable in the past (prior to this shootout). 

Mike did have some problems with the air-con which annoyed him greatly, but this was not a normal occurrence according to BGT. The only other area of concern was the poor fuel economy the ECU delivered. Overall however, the BGT fitted Microtech gets a very credible second. 

Unichip 
Regardless of driver preferences, when you consider the criteria on which each ECU was evaluated, a clear winner in the shootout emerges. The APS tuned Unichip not only feels the best to drive (and perceptively the fastest) but it leads in every category.  

The Unichip is the cheapest ECU on offer, has the best acceleration and offers the best fuel economy. Given fuel is about to hit the magic $1 mark, the better fuel economy alone has to make real cents. 

The Unichip makes good use of the existing factory settings for cold start, air temp compensation and other safety features so it can concentrate on making the car faster. There's no use re-inventing the wheel if you don't have to. 

Mike did report the customer service he received initially was not as good as he would have liked. Peter did make up for this by spending quite a bit of time with Mike in subsequent visits. I personally found Peter to be very helpful and he spent many hours with me talking about the tuning industry.  

The one aspect of the Unichip that does stand out is the part throttle response. In this area the Unichip blitzes. In traffic, a squeeze of the throttle gets you going whilst the others are still thinking about it. APS spend a lot of time on the part throttle response and it shows on the road.  

This is only half the story however. Peter Luxon and Robert Rapisarda have a wealth of experience with tuning WRXs and really know how to tune the car to optimise the performance. This is done without compromising engine safety and longevity. The Unichip ECU may be technically no better than other ECUs tested here, but the tuning ability and expertise of APS is second to none. Given this is the most important aspect of fitting an after market ECU, I wouldn’t go anywhere else.