Project GD Subaru STI Part Three- Making More Power with Greddy and Cobb Tuning

Project GD Subaru STI Part Three- Making More Power with Greddy and Cobb Tuning

By Mike Kojima

When we last left off, we had turned our STI into a G machine without giving up much daily driving comfort.  Now it was time for us to turn our attention to the engine.  The GD STI really responds to very basic tuning.

Just uncorking the car and spending a bit of time on the dyno can produce surprisingly big results for just a little bit of cash.  Let us show you how.

Doing the basics mean that at first it is a good idea to uncork the engine.  We did just that by choosing a Greddy RS exhaust.  We chose the Greddy because of its all stainless steel construction and large 80mm piping.  The Greddy uses 304 stainless which is corrosion resistant and polishes well.  The exhaust is laid out to have minimal bends which can cause a reduction of power.  The RS has a main muffler and a sub muffler.
The Greddy RS has this optional butt plug which goes in the main muffler if you want your car to be really quiet.  The butt plug probably has a loss of power so we left it off.  It takes about 3 minutes to remove or install.
Both the main muffler and the sub muffler are absorption type with a smooth perforated core.  These mufflers have essentially no backpressure and do not hurt performance.  The sound passes through the perforations and is absorbed by stainless steel wool packing backed by ceramic felt cubes.  This packing resists blowing out like typical fiberglass.
The RS uses these lightweight stamped flanges and thin wall tubing.  The RS saves over 20 lbs from the stock exhaust and is significantly lighter that most aftermarket systems without having to go to the expense of something exotic like titanium.

 

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