Subaru set the stage for this family rivalry. Back in December, the all-new 2015 WRX leapt into contention for our sports sedan dollars. Now the 2015 STI is doing the same, and it's bringing along a bunch of tried and true technology from its predecessor, including the port-injected 2.5-liter engine. At only 305 turbo-laggy horsepower, though, the STI ekes out just 37 more horsepower than the 268-hp WRX.

SEE THIS: De-winging the 2015 Subaru WRX STI

The Subarus 2015 Subaru WRX 2015 Subaru WRX STI Horsepower (mfr. claimed) 268 @ 5600 rpm 305 @ 6000 rpm Torque (mfr. claimed) 258 lb.-ft. @ 2000-5200 rpm 290 lb.-ft. @ 4000 rpm

Dyno Test

We know the STI is the best choice for railing down your favorite canyon, but could the more sophisticated turbocharged 2.0-liter engine of the WRX actually be the quicker, better option for everyday driving? We talked our friends at K&N into letting us horse around on their dyno and found out.

PHOTOS: 2015 Subaru WRX STI at NAIAS

Dyno Results 2015 Subaru WRX 2015 Subaru WRX STI Horsepower 223 hp @ 5800 rpm 247 hp @ 6400 rpm Torque 245 lb-ft @ 3850 rpm 243 lb-ft @ 5000 rpm

Lag Torture Test

Perhaps more telling than peak horsepower and torque figures are improvements to turbo lag. Senior Editor Jason Cammisa concocted a test that would illustrate the differences between the FA engine in the WRX and the older 2.5-liter in the STI. Look at the dyno chart below and follow along as we analyze the torque results.

At the beginning of the test, both engines are producing about 130 lb-ft after one second of throttle.

At the 2-second mark, the STI is up to 135; the WRX is already at 165 lb-ft.

At the 3-second mark, the STI is only at 140 lb-ft. The WRX is at a whopping 180 lb-ft!

At the 4-second mark, when the STI has managed to get to 145, the WRX is nearing 190.

At the 5-second mark, the STI is just pushing past 150 lb-ft; the WRX is nearing 200.

And when the WRX is making full torque (210 lb-ft in this case), the STI is only at 165.

READ THIS: This is the 2015 Subaru WRX - UPDATED!

What the graph shows is that the WRX can get to full boost in about 6.75 seconds, while the STI takes about 9.5 seconds. It's a big difference, but more important is what happens in the meantime as boost is building. That improvement in turbo lag is a big help on the road, where throttle input is more modulated and running to the top of the tach is a little obnoxious.

When you want to hustle on the track, though, there's no question which car to choose. We took both cars out for our complete battery of tests; you'll see the results soon enough. For now, we'll just show you the very impressive acceleration times.

PHOTOS: 2015 Subaru WRX

Acceleration

2015 Subaru WRX

2015 Subaru WRX STI

1 Foot (Rollout)

0.2

0.2

Rolling Start, 5–60 MPH

7.0

7.1

0–10 MPH

0.2

0.2

20

0.7

0.6

30

1.5

1.3

40

2.6

2.4

50

3.7

3.3

0–60 MPH

5.2

4.8

70

6.9

6.2

80

8.6

8.2

90

11.2

10.2

100

13.7

12.6

110

17.0

16.2

120

(no data)

20.1

Quarter-Mile

13.7 seconds @ 99.5 MPH

13.3 seconds @ 102.8 mph

Top Speed

174 mph (electronically limited)

155 mph (electronically limited)

We'll be bringing you complete test results for both cars soon. In the meantime, here's what happens when you leave us alone with a wrench and two Subarus.

Correction:The top speed notations crossed out above are incorrect. They were erroneously included in the final draft. We regret the confusion this may have caused.

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