How Did I Get 30 MPG In My Subaru WRX???

The Subaru WRX is known as a turbocharged rally monster, not a fuel sipping economy car. My WRX, with its FA20D engine rather than the EJ257 of the STi, is rated at up to 21 MPG city, 28 MPG highway, 24 MPG combined. With no aftermarket parts and a COBB Stage 1 tune, I’d expect real life performance to be slightly worse, thanks to a more performance oriented engine map. Imagine my surprise when I filled the tank, drove 40 miles to work in mixed highway and city conditions, and recorded an average of 30.3 MPG. I wasn’t even trying to hypermile or drive any differently than I normally do.

Here’s the even more stunning part. My BRZ used the same engine with no turbo and Toyota’s D-4S port and direct fuel injection, rather than Subaru’s home grown direct injection on the WRX. The 86mm/86mm bore/stroke are identical in both cars, and the wingless BRZ’s drag coefficient of 0.29 beats my WRX’s 0.32. Yet I couldn’t average better than 28 MPG in my BRZ, despite it appearing to be the more economical configuration. The only time I ever broke 30 was the long highway slog to Pennsic, and I never hit anywhere near the BRZ’s EPA highway rating of 34.

Justin's 2015 Subaru WRX

It’s true that resetting trip odometer A in the WRX also resets your fuel economy data. I’ve had readings well above 40 MPG on the two mile trip home from the nearest gas station. That’s not nearly enough distance to get an accurate reading, so I throw that out as a statistical anomaly, because SCIENCE! But I’m not the only one to get better gas mileage than the EPA numbers with a WRX in the real world. Motor Trend included the 2015 WRX on their list of 15 Cars That Get Better Mileage Than Their EPA Estimates, with a combined 27.2 MPG in their tests. That’s not as good as my 30.3, but significantly better than the EPA’s 24 MPG estimate.

I’m still an outlier, though. Fuelly says differently.

Based on data from 279 vehicles, 13,636 fuel-ups and 4,174,632 miles of driving, the 2015 Subaru WRX gets a combined Avg MPG of 24.08 with a 0.08 MPG margin of error.

It doesn’t get any closer to confirming the EPA’s estimates in the real world than that. So what’s different about my car? Although this is the first time I’ve broken 30 MPG, I’ve regularly seen 28-29 on my daily commute – meeting or beating the highway estimate with a commute that’s half highway, half city.

Justin's 2015 Subaru WRX

But I’ll bet many of those people aren’t running a COBB OTS Stage 1 93 octane performance tune. There is an economy tune available on the Accessport, but I’m definitely running the performance tune, not economy. I reached out to COBB support and asked if they could tell me anything about this particular tune that might be contributing to my excellent fuel economy.

“While we don’t advertise fuel economy improvements, generally, due to optimized tuning, customers can occasionally see a slight improvement in fuel mileage under average driving conditions,” said Matthew Bryant of COBB support. This makes sense to me. Optimization is optimization, and even if the focus of this particular map is on power and performance, it’s not surprising that a more optimized tune could improve fuel economy as well.

The bottom line is, don’t get a COBB Accessport specifically for better fuel economy. But don’t be surprised if you get some anyway as a beneficial side effect.

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  • Do the math yourself instead of the OBC. It’s likely generous.