Mitsubishi Lancer Evolution IX - EVO IX Power Tweaks, Part 2

On the dyno it was hard to determine the effect of the airbox. Although the wideband indicated that our air/fuel ratios were nearly unchanged, the airbox allowed the turbo to spool sooner and increased airflow. The flow increases and subsequent increases in cylinder pressure caused the engine to sport a knock count of over nine, and the ECU was pulling enough timing for the power readings to be awash. The ECU's timing curve would need a retune at this point if we were to see a gain from the airbox. The airbox simply worked too well for the tune at the moment. Another plus, we noticed a reduction of intake air temperature of 12 degrees. We couldn't readily explain this, but many people have observed how the ARC box partially sucks underhood air.

Since we had a relatively high knock count we decided to install XS Engineering's front-mount intercooler before retuning. The XS intercooler has a large tube and fin heat exchanger that's wider and thicker than the stock front mount. The tube and fin core also has a lower fin density than stock. While it would seem like this is a bad thing, the lower density actually allows the cooling air to penetrate more easily into the thicker core, improving efficiency. It also allows more cooling air to pass through the intercooler to reach the engine's radiator, helping to improve overall cooling.

The XS intercooler was a direct bolt-on and only took about a half hour to install while the car was strapped to the dyno. We once again did some pulls and found that the intercooler eliminated knock count across the map and gave us around 8 whp. From this starting point XS Engineering's ace tuner Koji Arai went to work. Koji was able to add quite a bit more timing to our ignition map without increasing knock count and, with a combination of adding more timing and more cam advance to our Mivec system, he was able to extract 9 more hp, leaving us with an impressive 321 whp-a whopping gain of 17 whp just from the intercooler. The power gains were huge and across the board.

We considered adding more timing and fuel or possibly tweaking the boost but when reviewing our data logs, we realized that we were completely out of injectors as we were at 100 percent duty cycle in the last two load columns of our fuel map. Although some tuners in other states have extracted more power with equivalent mods, we feel that our 321 whp is pretty impressive for our exceedingly crappy 91-octane pee water fuel.

Stay tuned; we have some big RC Engineering injectors and more parts waiting in the wings. We intend to see how far the stock turbo and bolt-ons can be taken with California's weaksauce pump gas. Once we max that out, we intend to test a bolt-on turbo upgrade and eventually even bigger and better things!