That's sort of a tricky question. Usually, when you modify your car to increase power, you'll end up losing mpgs. No matter what you do, you probably won't be able to noticeably increase your mpgs, but rather sustain it or keep it from significantly decreasing as you add power. Much of your gas mileage has to do with how you drive the car and it is possible to average low to mid 20's (sometimes better) with a slightly modified WRX.
If you get a Cobb AccessPORT, a bellmouth downpipe, flash to a Stage 2 map, AND you can keep yourself from mashing the gas pedal to the floor all the time, you might pick up a few extra miles per gallon, but you'll also get a noticeable power increase over stock. An up pipe would benefit you as well, but mostly as a safety mod so your pre-turbo catalytic converter doesn't break apart and send chunks of debris flying into your turbo, often causing catastrophic turbo failure. Turbocharged engines can actually be more efficient than naturally aspirated engines depending how you drive them, but most of us would rather feel the car push us into the seat over and over. A K&N filter is also a good idea. Pulstar Pulse Plugs advertise better gas mileage and an increase in horsepower/torque, but they're pretty expensive. I have a set of them right now and, although there might be an improvement in all of that, it's not noticeable. You could also switch to synthetic engine oil, transmission fluid, and rear differential fluid - and, actually on that note, make sure all of your maintenance is up to date and you'll probably pick up a few mpgs and restore some lost power.
I put a stage 2 map on my car and I did see increase by 4 MPG on a road trip vs the same route without EM. BUT that is not always the case. With an increase in power it is hard to keep from having a lead foot. I end up with the exact same mileage as before so I actually am saving gas by having more power. Get a boost gauge installed and anything above 0 psi is boosting and costing more in gas.
You will be able to hear the inake, the turbo and the BPV a little more, as far as help Im not sure. And if you get the AP, dont mess with the economy map. Its meant for light driving only. It pulls boost and all that to "conserve" gas, but in turn you have no power if or when you want to pass anyone. When I was both stage 1 and 2 I got just as good or better gas mileage as the economy map, and I was able to pass when I wanted to also.
If it helps, I just put in a drop in K&N on Friday, noticed alittle less in mpg but got more performance out of it (09 stock wrx) but I was having fun and was hittin alot of boost in the process. Going to fill up and lay off the pedal this time to check mpg #'s
I wouldnt get a CAI unless you plan on tuning the car right after installation. If you want an intake (which is not needed until heavier modding is done) get an SRI like the Cobb or the SPT. They are the same ID as the stock intake and wont mess with the MAF or anything.
Buy an accessport in the nasioc classifieds you should be able to find version one for less than 350, and really there is no great advantage to version 2. When you get bored with stage 2 add a sti top mount and a spt intake and lookup clark turner etunes, holy crap the power over OTS stage 2 is bad.
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.