Cobb Accessport - ECU Tuning - Stock vs. Stage 1 vs. Economy Tune
 

Hi everyone,
I picked up a Cobb Accessport (AP) to dip my toes into ECU tuning to eek out some more mpg's on my 2013 Wrx Sti. The "word" in the Subaru forums is that the AP will increase 15 HP and 53 lbs torque while not losing any mpg's. Some users are even claiming 2-3mpg increase. All of these mpg claims were anecdotal, so I decided to put the claims to the test.

http://i101.photobucket.com/albums/m...5a963a27ea.jpg

You can find these used for about $300-350, depending on which "version" you get. Mine is an older "version 2" that I bought used for $330.

Testing Info:
0.75 mile loop in an industrial park, Set cruise control at 30mph in 5th gear, drive around in circles making notes of "trip mpg" on SG II at pre-determined "start" and "end" points, Reset SGII after every lap.

I did 3 laps of every "tune," and here are the averages

Stock Tune: 35.53 mpg
Stage 1 (91 octane, 47 state tune): 36.5 mpg
Stage 1 (91 octane, Arizona, California, Nevada tune): 36.67 mpg
Economy Tune: 37.43 mpg

Just for fun, I ran 3 more variables (while on Economy tune)

A/C On: 32.6 mpg
Windows full down: 36.5 mpg
Windows half down: 36.9 mpg

Impressions:

Stock vs. Stage 1 (Ariz, CA, NV tune): 1.14 mpg (3.1%) increase compared to stock. it's not quite the 2-3 mpg increase as claimed, however, an extra 15hp and 53lbs of torque with no loss in MPG's is amazing.

Stock vs. Economy: 1.9 mpg increase (5%) compared to stock. It's closer to the 2-3 mpg increase as claimed, however, there is definitely lack of power (peak boost is only 8lbs).

A/C vs. Windows: it appears to be more fuel efficient to run your windows half down than it is to run your A/C. However, at highway speeds, I suspect aerodynamic drag will come more into play with the windows rolled down.

Conclusions:
Perhaps, the 2-3mpg increase on a Stage 1 tune can be found somewhere else on the rpm/load/bsfc range such as at highway speeds and in 6th gear? However, there are too many variables to do accurate testing on the highway. I also don't know the best BSFC for this car yet, so perhaps 30mph in 5th gear is not quite the most "efficient" in terms of BSFC.

Is $330 worth it for a 1.9 mpg increase?

How about, is $330 worth it for 1.14 mpg increase, with EXTRA POWA?!

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On a side note, I got pulled over by the police because a security guard thought that I was scoping out the place because I was driving around in circles, lol! The cop told me there have been reports of robbery in the area, i explained to him what I was doing, he let me go on my merry way.

It's worth it!
This past May, I installed an underdrive crankshaft pulley on my Mustang. More power to the rear wheels and about a 1 MPG gain for ~$310. It will pay for itself in fuel savings in around 80K miles. But "bragging rights" are immediate! :thumbup:

Is this a tuning AP where you can change parameters or a stage only?

The AP itself only let's you upload stage tunes. However, Cobb does offer tuning software for free that lets me customize tuning parameters. However, ecu tuning is way out of my league.

Sweeeeet. I'm not very educated on these matters, but I would imagine most FE in that test would also be best on the highway. Did you do 3, then 3, then 3, or did you do 1, 1, 1, then 1, 1, 1, so on?

I did 3,3,3 because it was more efficient this way. If I did, 1,1,1 then I'd have to shut the car off, reflash, then start the car again.

My only concern is that the longer the car was on, the better the results were. If you went back and did Economy, then cali, then 47, then stock, would it look the same?

I see what you're saying. When I have time this weekend, I'll go back and do the runs in reverse order.

I completely understand the frustration and challenge of testing, I mean the feedback as constructive :)

This tuner affects the AF ratios.

OBD gauges use MAF, RPM and load to work out fuel consumption. They assume the same stoich AFR whether the tuner is plugged in or not.

Therefore I don't think a OBD gauge can be used to test plug in tuners or ECU reflashes.