Intercooler outlet to throttle...
Intercooler outlet to throttle body as installed.
It's a well-known fact that the Karman mass airflow meter-equipped EVO is sensitive to change. Even simple modifications can play havoc with air/fuel ratios as the MAF can easily be thrown out of whack. Usually, ECU tuning is required to get the most out of any modification, especially when dealing with modifications positioned pre-turbocharger. Another issue: factory timing maps are optimized for 93-octane gas and are just too aggressive for our crappy California 91-octane pee water. The EVO ECU monitors knock; as knock counts rise, the ECU pulls timing. And if they get too high, the ECU switches to less aggressive high-octane and even several different low-octane maps to better protect the engine. This makes for inconsistent operation.
Mitsubishi's ECU tune fails to take advantage of all MIVEC has to offer. With a full 27 degrees of intake camshaft adjustment possible, the stock system only makes use of roughly half that. Large low and midrange power gains can be had through MIVEC tuning. All is likely this way for emissions reasons.
XS Engineering's Koji Arai fired up his laptop for a quick ECU reflash using their stock vehicle/cat-back exhaust program. The XS flash tweaks fuel, ignition, MIVEC maps, boost control tables and raises the rev limit to 7,800 rpm. One advantage with ECU reflashing versus piggyback systems is that the former does what it does in the same way the factory gets things done. With piggyback devices, Mitsubishi's ECU is forced into a figurative tuning fight with the piggyback ECU, automatically adjusting fuel and spark trims that are constantly trying to return to normal parameters. Because of this, inferior piggybacks can often run well at first and then begin to conflict with the ECU resulting in poor operation. On an aggressively tuned setup this isn't just annoying, it can also be potentially dangerous for the engine's health. Another advantage to reflashing the stock ECU is that all of the factory's electronic safeguards for overboost, knock detection and overheating remain intact.
Intercooler inlet pipe as...
Intercooler inlet pipe as installed.
Back at the dyno, XS' reflash results were amazing. We gained 5-peak hp, which means Project EVO's pumping out a good 289 whp at 7,100 rpm. This only tells a fraction of the story, though. Power gains are huge across the board, as much as 18 whp in certain spots. We picked up power from idle all the way to fuel cut. Each power curve dip and squiggle was filled in nicely with hardly any drop at all as we approached fuel cut. The results are a solid wall of power from 3,000 rpm all the way to 7,800 rpm-a whopping 4,800rpm powerband. On the road, the car feels like a different animal with the turbo spooling much faster and always wanting boost. The seat of the pants feel is even greater than dyno charts would suggest. On a side note, we believe XS' reflash to be extremely safe, perhaps even safer than the stock program as knock counts are fewer and dyno pulls are far more consistent. Had we known about all of these positive benefits, we would have probably flashed the ECU as a first step. The XS reflash was, by far, the best thing we have done to date.
Overall, Project EVO pleases us. With a few simple bolt-ons and our ECU reflashed, we picked up nearly 30 whp across the board from idle to fuel cut. Project EVO currently feels exactly how we believe it should feel straight from the factory. Stay tuned; we'll be working on our IX in an effort to find out how far we can push it with its stock turbo and even more simple bolt-ons.
 XS Engineering's ECU flash...  XS Engineering's ECU flash revealed impressive gains throughout the powerband. This was the best mod we tested and showed considerable gains in areas under the power curve. |  Compressor discharge to intercooler...  Compressor discharge to intercooler as installed. |  Almost a 30hp increase with...  Almost a 30hp increase with large gains across the powerband; not bad for just a little work. |