Street Friendly (And California Legal) GD Subaru STI Build! Part Three, Getting Some Green Power With Cobb Tuning

The STI is fully street legal even if you are forced to pop your hood, the CARB EO sticker is right there to see. Our car needed a new fuel pump so we installed a DW340 to replace the tired stock part.  We also had a Cobb Pro Tuner make some minor adjustments to the tune to make up for the slightly higher fuel pressure of the new pump.  Our car made close to 307 whp, up from the stock 246 whp.  Now, this is slightly more than what the pure off-the-shelf tune would do which we think would be around 290-300 whp.  This is still nothing to sneeze at and it is more powerful than our own Project STI was with slightly more bolt-on parts!

The car is now pretty much ready to give back to its owner.  Our mods have transformed the car making it very pleasant to drive with lots of gains in performance but no deterioration in ride comfort or engine drivability. Everything is CARB approved, the emissions are clean and it still makes respectable power while still being green.  The whole package is nicely refined, like it was a factory package one step higher than a base STI. Our only recommendations to add to the car would be a set of lightweight wheels and bigger stickier tires.


Cobb Tuning


  1. I know there was a lot of complaining when Cobb decided to pull a lot of their parts recently, but I’m excited to see what they can do while still being CARB compliant, especially with Flex Fuel and down pipes. Hopefully this owner decides to do more if/when the Project Green Speed development is fully fleshed out so the readers can get a no BS article about what is and isn’t possible while following the rules. As dumb as they sometimes may be…

  2. Thank you for the great article. Do you have any recommendations for an aftermarket turbo intake duct? There are a number of options on the market. I’d love to know what your experience has been with them, which is your favorite, and why.

    It looks like the resonator chamber had already been removed from the fender. Cutting out the back of the air intake duct, as mentioned on page 9, seems like a good idea, especially if the resonator is gone. But, wouldn’t you also recommend blocking off the two giant holes in the inner fender wall which, without the resonator in place, expose the air cleaner to all the road grime blowing past the fender liner?

    Thanks again for the excellent content!

  3. I see you used the COBB titanium cat back, is this similar to the older COBB catbacks that neck down to 2.5′ at the area that mates to the downpipe, or would this be a true 3′ all the way through?

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