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

The tube is replaced by Cobb’s intake tube.  It has no flow restrictions.

Next, the cold air box is set in place. The box shields the air filter from hot underhood air.  Colder air helps in power production, usually, every 10 degrees drop in intake air temp results in a 1-1.2 percent increase in power.  This airbox can drop the intake air temp by as much as 40 degrees.

The heat shield is held in by the existing 10mm bolts and you don’t need to drill any hole or anything like that.  The coolant hoses from the radiator tank to the surge tank are rerouted along the side of the airbox.

This bracket now bolts into an existing bolt hole.  This is a hold-down point for the lid of the heatshield.


  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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