Mitsubishi’s Lancer Evolution caught on very quickly when it was introduced to us Yanks in 2003. The looks, the sound, and most importantly, the car’s reputation made the Evo a wanderlust to a salivating entourage of American enthusiasts. The car was pounced upon and quickly tangled with a familiar foe, it’s arch nemesis from the World Rally Championship days, the Subaru WRX. The battleground was not gravel and tarmac, but the aftermarket. The latest iteration of the marque, the 2008 Evolution X, marked a tentative step forward with a radically different body shape and a new motor to replace the long-running and formidable 4G63.

Mitsubishi’s 4B11 improves on some of the shortcomings of the original motor. The motor is square, meaning the stroke and bore are equal, which allows it to rev to the moon with built internals. Though it loses the indestructible iron block, the new aluminum composition is strong enough and can withstand 800 wheel horsepower without sleeves. It’s a well-rounded, sturdily-built powerplant so we took it upon ourselves to see what a few bolt-on upgrades and a bit of tuning can extract from the Mitsubishi.

Despite a respectable baseline, we still felt that the true potential was hampered by restricted airflow.

Before wrenches turned and parts started flying, we visited GMG Motorsports where the Evo laid down a baseline of 240.8 whp and 259.0 lb-ft of torque … not bad for a stock car on a conservative tune. The blue line, representing the torque curve, shows what a modern turbo engine is capable of. With torque peaking around 3,200 rpm and plateauing until 4,600 rpm, a strong mid-range thrust that gives the impression the 4B is more powerful than it is. Though that peaky, archetypal, mule-kick power delivery may feel fast, accessible torque is what determines real-world speed. Smooth and progressive, the power delivery is indicative of a refined turbocharged engine.




To bring a little more out of the motor we added a front mount intercooler, charge pipes, and an induction system, all from AEM. These parts are designed to fit within the confines of the stock pieces without any cutting or clearancing. The intercooler improves flow and cooling. By expanding the size of the inlet end tank inlet re-circulation and pressure drop were reduced considerably. Within the inlet tank, a specialized air vane guides the air over the intercooler, improves distribution over the core, and improves overall surface area contact. By adding an extra port in the intercooler’s discharge tube, auxiliary devices likes water injection nozzles, temperature probes, or boost pressure sensors can be fitted. Clearly, the guys at AEM have long-term tuning in mind when they develop parts.

AEM FMIC & Pipe Kit

  • FMIC $681.99 Suggested Retail
  • Pipe Kit $365.99 Suggested Retail
  • Mandrel Bent Tubing
  • #2102-A (FMIC) Available For 4B11
  • #2102-B (Pipes) Available For 4B11

AEM Cold Air Intake

  • $298.99 Suggested Retail
  • Durable Grey Powdercoat Finish
  • Washable, Reusable Dryflow Filter Media
  • Up To 17.0 hp At 4,100 rpm
  • #21-678C Available For 4B11
Building upon the gains from the intercooler body are the charge pipes. With increased diameter, the pipes improve flow and help, purportedly, increase mid-range power. AEM’s charge pipes’ sturdy composition, unlike the silicone/rubber originals, do not expand under boost nor become dry and brittle over time. Though the intercooler itself won’t be turning heads, the charge pipes are available in an industrial graphite grey color and add a little spruce without attracting too much attention.

AEM designed its replacement intercooler with similar dimensions to the stock unit and a headache-free installation in mind. The first step is to remove the plastic covering and its integrated air duct which sit above the intercooler/radiator assembly. After removing the fender liners and the three-piece belly pan, a matter of a few bolts and clips, the lower grille mesh is removed and the fog light wire loom disconnected. The bumper is now ready for removal.




Among the added parts, the real game-changer is the AEM intake system, and while it impresses on aesthetics alone, horsepower is the end game. With the same grey coating as the charge pipes, the intake pipes accent the engine bay in a tasteful, subdued fashion that savvy enthusiasts will notice with a quiet nod of approval. The airbox itself looks quite factory, however, so it still keeps a low profile. Predictably then, the airbox fits in the OEM location. The design reduces intake temperature by isolating the filter element from the ambient temperature better and by using a higher grade filter to flow a higher volume of air to the engine.

Thanks to the straightforward installation process, most of our time was spent tightening bolts instead of scratching our heads.

The stock charge pipes are removed but the nuts are retained for the replacement parts. Detach the re-circulation hose, loosen the charge pipe couplers and remove the rubber grommets from the intercooler end tanks. The stock intercooler is now ready for removal. After removing some of the ancillary parts, a second set of hands was needed to position the AEM intercooler between the bumper beam and the radiator to prevent any accidental damage.

From this point the installation is fairly straightforward: fitting the new charge pipes, re-circulator tube, mounting brackets and fastening everything with the stock connectors. The process requires a bit of custom tailoring to the plastic cover removed in the first couple steps. The opening for the charge pipe needs to be expanded with a rotary tool to accommodate the newer, wider AEM piece. Other than that, it’s a matter of reattaching the aforementioned parts, checking clearances, and tightening accordingly. Thanks to the exemplary fit-and-finish, the installation is easy.

stock vs AEM

The dotted lines represent the gains made post-modification, pre-tuning.

Back on the GMG Motorsports dyno with the addition of the AEM parts, horsepower climbed to 268.3 whp and 261.4 lb-ft at the wheels.

The computer targets load, not boost. Load is what a more sophisticated, standalone ECU would read as manifold pressure. – Jon Drenas, 5150 Racing.

We enlisted the tuning talents of 5150 Racing’s Jon Drenas who told us that the minute improvement in torque was the result of a shortcoming with the 4B11’s ECU. “The computer targets load, not boost. Load is what a more sophisticated, standalone ECU would read as manifold pressure.” 

Continuing, Drenas explained, “In the stock ECU, load is derived from the MAP and MAF sensors and can change relative to the intake temperature and elevation. In short, it’s a vague indicator since load isn’t always the same as boost. When encountering the higher flow rates, the stock ECU strives to keep everything hunky-dory and within a conservative range. Even after adding the freer-flowing AEM components, the ECU reverted back to stock settings, hence the minuscule torque gains.”




With 5150 Racing working their magic, our Evo stepped up to plate with the confidence of a heavy hitter.

With 5150 Racing working its magic, our Evo gained gobs of power and a wider powerband. There are 30-plus whp gains realized from 4,700 rpm to redline and improved torque throughout the run.

Undaunted, Drenas dialed in the Evo. He ultimately bumped the numbers to a solid 273.6 whp and 293.4 lb-ft. of torque. Most striking was the way the torque curve changed. Not only was peak torque reached earlier in the rev range, but the plateau had widened and the drop off was just as progressive as before. Considerable horsepower gains were found everywhere on the chart, with the biggest gains seen in the mid-range from 3,200 rpm to 6,400 rpm. Power built steadily and smoothly with a linearity one might not expect from a boosted 2.0-liter engine.

When comparing the car’s stock output to that of the tuned car, the differences are most striking. The overall horsepower gain was 32.8 whp and 34.4 lb-ft. of torque at the wheels, which, given the price of the modifications, is quite respectable. The whole tuning process was straightforward, and Drenas was quick to point to the 4B11’s ability to react to tuning inputs. “For one,” said Drenas, “the MAF sensor is much more sensitive than the Karman Vortex unit found in the 4G63. Secondly, the ECU is accommodating and modifiable.” The crew at 5150 Racing utilizes a customized version of the stock ECU with a modified ROM that allows the parameters to be changed. 

By using a modified version of the stock ECU, 5150 Racing were able to extract power without having to pony up for an expensive aftermarket computer.

By using a modified version of the stock ECU, 5150 Racing was able to easily extract power without having to pony up for an expensive aftermarket computer.

As mentioned earlier, the standard ECU reads load instead of boost, and when allowing the motor to breathe easier, the gains aren’t necessarily accounted for since the ECU will revert to a very conservative setting to ensure reliability. The Tephra V2 ROM 5150 Racing uses allows for boost control to be dictated by PSI rather than load. It also features knock indication, separate launch control maps, map switching, and fast logging. With Tephra V3, a flex-fuel setup can be used for any blend of ethanol and the ECU will accommodate for it.

For those considering the dollar-to-horsepower value of these upgrades, consider that not only was peak power brought up considerably, but the response, linearity of the power curve, and width of the torque-band were all improved. While peak power figures may earn bragging rights in the bar, real-world performance is subject to other factors. If you’re looking to make your Evo X keep up with quicker, more expensive machinery on the backroads and highways and not break the bank or give yourself an aneurysm in the process, these are great initial mods that will continue to pay dividends as more performance parts are added. With a few hours invested, you’ll give your Evo X that extra bit of fine tuning it deserves and keep the door open to big-time power.