After seeing how well AEM’s air intakes worked on the new Subaru STI and the new turbo FA20 powered WRX, we couldn’t resist another AEM + Subie dyno test, this time using a 2015 Forester XT. And once again Travis from Snail Performance is our official dyno tester. He’s a long-time friend of ours and we really trust his tuning and his professionalism when evaluating parts. He’s like our Texas-born, Cali-living brother from another mother.
The nice thing about the shiny, new FXT Travis used for this test is that it was 100% stock, so the results show you exactly what bolting up AEM’s intake system does when combined with a Grimmspeed 3-port electronic boost control solenoid and a Cobb AccessPort V3 pro tune from a Plus Key Wizard like Travis. As you’ll soon see, this $1,000 package of goodies provides some seriously impressive results.
Of course before testing these parts on the dyno they needed to be installed. The AEM intake system uses a mandrel bent aluminum air intake tube that features smooth radius bends and a powder coated finish in an attractive Charcoal Gray colour.
The AEM Dryflow air filter is positioned more or less where the stock airbox used to live, in the front passenger side corner of the engine bay. With the help of the Black powder coated heat shield, AEM has done their homework to make sure the filter is sucking in the coolest air possible. The kit also includes all the hardware and instructions needed for a quick and easy installation, plus it comes with a Lifetime Limited Warranty, just like all of AEM’s kits.
When we asked George Hsieh from AEM why they didn’t integrate the factory air scoop into the shield like they did with the WRX FA20 DIT kit, he had this to say: “We did entertain the idea of setting up the heat shield just like the WRX to take advantage of the pressurized air feed. However, we decided not to go with it due to the scoop’s location limiting the size of the air filter we can use with the kit. In addition, we’d have to ask customers to cut the scoop to have it properly interface with the heat shield. We have performed temperature testing via thermocouples and the area where the filter resides gets plenty of fresh air through the lower bumper openings, utilizing a semi closed heat shield we were able to keep the fresh air supply isolated to the air filter. The location of the MAF also plays an important role. By placing the MAF lower in the tube ensures accurate air flow and temp signal pick up for consistent gains.”
The Grimmspeed EBC solenoid uses a 3-port design rather than the OE 2-port, which gives Travis higher resolution boost control, aiding spool up and providing tighter control of boost levels across the entire powerband. As you can see, it includes a Plug & Play harness so it just plugs right into the factory harness, is voltage matched to work seamlessly with the factory ECU, and the mounting bracket means it’s literally a 10 minute install.
The Cobb AccessPort V3 is even easier to install, since all you do is plug it into your car’s OBD port. So ya, literally a 30-second install, and the control this cell phone sized device gives you is impressive, since it allows pro tuners like Travis to completely remap fuel and ignition timing as well as fine-tune boost pressure, cam timing and much more, but it’s also user-friendly enough for non pro tuners to upload Cobb’s Off-The-Shelf tunes or even use it as a diagnostic tool whenever a CEL pops up. And thanks to its full colour display, it’s also a very handy and customizable gauge for displaying all sorts of engine data, from air/fuel ratio to the temps and pressures of your choosing.
With the installation work complete, Travis strapped the FXT to his Mustang chassis dyno and spun the Subie’s turbocharged FA20 to redline a few times while dialling in the tune.
Bam! As you can see, this Fozzie XT saw huge gains in horsepower and torque, with peak torque jumped from 218 to 287 ft-lbs and area under the curve torque gains are massive right across the entire powerband. Peak horsepower improved tremendously as well, going from a baseline of 209-whp at around 5,600 RPM to 244-whp at around 5,400 RPM and gains are even bigger in the mid-range. This thing just went from Soccer Mom Subie to Sleeper STI Status in a hurry!
Part of the 69 ft-lb and 35-whp peak gains can be attributed to the 3-4 extra PSI of boost pressure the FA20 is seeing after Travis’ tune, as depicted by the green lines of the dyno chart. The dotted green line for the stock baseline shows a fair bit of change in boost pressure across the rev range, while the Grimmspeed EBC and Snail tune have boost under much better control as seen with the smoothness of the solid green line.
Travis’ tune has smoothed out and richened up the air/fuel ratio, too, which no doubt contributes to its improved power output, especially below 4,700 RPM where the factory tune is surprisingly lean for a turbo car. Not dangerously lean by any means, but definitely a factory tune with fuel economy in mind more so than peak power production.
AEM’s far less restrictive air intake has also contributed significantly to the overall gains, their advertised 23-whp and 18-wtq accounting for most of the gains in top end horsepower and about 20% of the torque gains, too. Plus, as the above comparison of ambient air temps vs intake air temps show, the AEM intake system does a remarkably good job of sheilding the air filter from hot engine bay air (made hotter by the turbo system) and feeding the combustion chambers a cool, dense air charge that’s less than 5-degrees warmer than ambient at low engine speeds and less than 2-degrees warmer than ambient from 4,400 RPM to redline.
In the end, the owner of this stealthy looking ’15 FXT now has STI-like power production for an investment of around $1,000 ($275 for the AEM intake, $110 for the Grimmspeed EBC solenoid, and $650 for the Cobb APV3). That’s some serious bang for the buck in our books, not to mention a great way to surprise the occasional Evo owner once the stoplight turns green.