My 2009 WRX Hatch

[Vansquish]

Is it really bad enough to need an engine-out service at 5 years old? I'd hope that Subaru engineered that puppy better than that!

As for mods, I believe that a Cobb AccessPort, and a few flow mods (downpipe/intake/larger intercooler) are probably enough to really open her up. Tuned properly, you'll be able to eke out some better fuel economy too.

[nthfinity]

Originally Posted by Vansquish Is it really bad enough to need an engine-out service at 5 years old? I'd hope that Subaru engineered that puppy better than that! As for mods, I believe that a Cobb AccessPort, and a few flow mods (downpipe/intake/larger intercooler) are probably enough to really open her up. Tuned properly, you'll be able to eke out some better fuel economy too.

No, it doesn't "need" an engine out service... it just allows me to change a few more things more easily in the process.

I get concerned with leaning out too much, as there is always 1 cylinder who needs the extra "cooling"; but I definitely expect better economy after the tune/mods this summer.

[Vansquish]

Originally Posted by nthfinity No, it doesn't "need" an engine out service... it just allows me to change a few more things more easily in the process. I get concerned with leaning out too much, as there is always 1 cylinder who needs the extra "cooling"; but I definitely expect better economy after the tune/mods this summer.

The cooling effect of the fuel is mitigated somewhat by the fact that the WRX motor isn't direct-injected. In my car, the injectors actually do spray a fine mist of fuel that, in part, washes down the cylinder walls providing some evaporative cooling. Port-injected engines have more difficulty doing that, as the air/fuel mixture is already formed prior to the fuel entering the combustion chamber.

I'm not sure exactly what the specs on the WRX engine and OE tune are, and I suspect they're pretty dramatically different from what was on my car.

Stock, my car ran ~14.7:1 AFR at cruising speeds and under low load conditions. At WOT, the mixture tapered down to about 9:1 (which is pretty ridiculously rich) to avoid knocking, particularly with bad fuel.

Since the compression ratio of the MZR DISI is a relatively high (for a turbo motor) 9.5:1 and it runs 15.5psi of boost in OE conditions, there is a pretty high probability of knocking if you run poor quality fuel or in very hot conditions. That said, with the appropriate monitoring tool(s), and air-flow/cooling modifications, it's safe to run around 16.5:1 - 17:1 AFR in low load conditions, and cruising, and a somewhat more aggressive 11.4:1 - 11.8:1 AFR at WOT. There are noticeable performance gains to be had by doing so, both from a WHP/WTQ standpoint, and from an economy standpoint. In addition, I'm running about 3psi more boost than stock, and I have advanced my ignition timing by a few degrees as well.

I can also monitor a variety of other parameters that aid in determining whether combustion temperatures or EGT has risen to such an extent that there's a serious risk to the valvetrain, exhaust, turbo, or other components.

Anyway, you might well be able to run a bit more lean, with a bit more ignition timing, and a bit more boost, and still be well within the "safe" tolerances of the motor. Furthermore, since if memory serves, the exhaust system on the '09 WRX has equal-length exhaust headers, and intake runners, the likelihood of having a serious imbalance in the amount of air/fuel flow seems like it's probably going to be relatively small.