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Project GD STI - Improving the Fuel System with Injector Dynamics and Other Details

By Mike Kojima

 

When we had last left off on Project STI's engine, we had just upgraded the cooling system in anticipation of another round of tuning.  What was supposed to be just some routine installation of a few parts to get a little more power ended up being something a lot more complicated, time consuming and involved.

 

Read more about MotoIQ Project GD STI!

 

We used Cobb Tuning's down pipe to complete our exhaust.  The Cobb downpipe is a really nicely made piece fabricated from 3" 304 stainless steel.  It is quite a bit bigger than the stock downpipe.  The Cobb downpipe cones with a high flow catalytic converter.
The Cobb downpipe on the right has a cavernous turbo outlet investment cast from stainless steel.  This gives a lot more space for the wastegate discharge to flow.  The stock downpipe has a shallow cutout while the Cobb part is more like a big funnel for the exhaust.  Using a casting here allows Cobb to make a complicated part with large interior volume capable of fitting into a tight area.  The tooling for this is quite expensive but the results are worth it.
The juncture of the turbine discharge casting to the tubular downpipe is fish mouthed to have more weld area for improved strength.
The quality of the Cobb part is amazing.  The wastegate discharge has a cast in fitting to allow for a wideband 02 sensor to be used when tuning.
The Cobb downpipe fits well with no interference with other parts underneath the car.

 

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Comments
av240
av240link
Monday, December 17, 2012 2:25 PM
Can't wait and see what you guys have in store for the weak USDM trans.
Mike Kojima
Mike Kojimalink
Monday, December 17, 2012 2:37 PM
To our knowledge the 6 speed transmission is fine.
benjim
benjimlink
Monday, December 17, 2012 7:22 PM
The 6 speed will be fine. Most likely av240 is referencing the early model gd 5 speed transmissions.

Any chance of selling this clean specimen later down the road?
Der Bruce
Der Brucelink
Monday, December 17, 2012 9:16 PM
Excellent, in-depth and insightful as usual! When does the drop in turbo replacement go in? 400whp..........
6SPD_soul
6SPD_soullink
Tuesday, December 18, 2012 5:30 AM
I guess I'm weird. I thought the coolest part was Howards low profile impact driver, that shit is genius.
Wes Dumalski
Wes Dumalskilink
Wednesday, December 19, 2012 1:56 PM
^ agreed. The rest is good but Howard just seems like an amazing wrench!
Mike Kojima
Mike Kojimalink
Wednesday, December 19, 2012 9:24 PM
This crap still took us 4 days!
ohmfab
ohmfablink
Sunday, January 13, 2013 6:31 PM
Any info on the manual low clearance impact driver shown on page 9?
Mochajoe
Mochajoelink
Wednesday, July 16, 2014 10:01 AM
I just bought a fluidampr and the tool for my 05 STi based on this review! The tool is called PowerBar, if you search "Powerbar Hand Impact Wrench" in google you can find it. My particular unit is the same one Howard uses made by Matco.
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