For engine control, Shiv first flashes the factory ECU with a performance base program using the Xflash tuning system. The Xflash is an ECU reprogramming system for the EVO that is capable of revising all performance-related engine control parameters. The high- and low-octane fuel tables, high- and low-octane ignition timing tables, adaptable knock control logic, injector scaling, boost limits, rev limits and speed limits can all be modified depending on the application.
For our application, we needed something more than just an ECU reflash. We needed something that would allow us to have multiple maps for race fuel and water injection operation. To allow multimap capability, Shiv installed his user-programmable XEDE piggyback ECU to work in conjunction with our Xflashed stock ECU (which itself was only remapped for higher boost and rev limits). The XEDE is a sophisticated piggyback ECU capable of altering every critical signal input and output of the factory ECU. This way it avoids the typical pitfalls of piggyback ECUs, fighting the factory self-learning control.
The XEDE has some drawbacks though. It cannot raise the rev limit, speed limit or boost cuts (that's where the XFlash comes in). Like a typical piggyback, it must alter the MAF sensor's signal to trim for larger injectors. This used to be a significant disadvantage because altering the MAF signal can also put the engine in the wrong cell of the spark table. This, fortunately, is easily accounted for due to Vishnu's knowledge of the factory ECU tables.
We drove Project EVO to Vishnu's Northern California headquarters for a tuning session with hopes of exorcising our car's low-octane demons for good. At Vishnu, Shiv strapped Project EVO to the rollers of his Dyno Dynamics AWD dyno and went to work by first downloading an Xflash to the factory ECU. Next, Shiv installed the XEDE and revised the factory fuel and timing maps. Finally, he experimented with different cam timing scenarios only to determine that our prior settings were close to optimal for the Tomei camshafts.
About then we ran into our first problem. After many pulls our air/fuel ratio started to get inconsistent, fluctuating between normal and lean. Turns out our fuel pump was overheating and losing efficiency. According to Shiv this is a common problem when the stock fuel pump is being pushed to its limit. The fuel pump was quickly swapped out for Vishnu's 255 liter per hour high-capacity pump and we were back in business.
With the stock ECU tune, our boost pressure would vary from run to run, from as high as 19 psi to as low as 15 psi depending if detonation was detected. Shiv set our boost at 20 psi and raised the rev limit to 8000 rpm, removing the speed cut. He also modified the fuel and spark maps and limited the amount of knock retard.
After perfecting the 91-octane-specific XEDE map, Shiv wired the XEDE to control our Aquamist water injection. He then developed a specific water-friendly map, advancing the timing and leaning the mixture slightly. Since we plan on using the water mostly as a thermal control when running the car at the track on hot days, Shiv was conservative and did not push the limits of the water's anti-detonation capabilities.
Driving Project EVO on the long trip home to Southern California, we were amazed at the difference in power and driveability. The throttle response was greatly improved and the turbo spooled faster. We are also getting slightly better fuel economy. We were eager to return to XS Engineering and check the power output compared to our last dyno sessions. The car felt powerful and we were eager to see just how much more powerful it was.