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


Here is a good view of the polished rear section of the Greddy RS exhaust.
Our car came with this Subaru factory SPT intake.  SPT is like TRD is to Toyota or Nismo is to Nissan so you know it is a well designed part that is smog legal and warranty friendly.  We will be comparing it to Cobb’s own intake in the near future.  Subaru’s are very sensitive to anything in front of the Mass Airflow or MAF sensor and many cold air intakes actually need to have the car retuned or engine damage can occur.  This is because Subaru’s have some unusual tuned conditions from the factory which we will explain a bit later.  The SPT intake and Cobb’s intake are designed not to throw off MAF readings.
Before installing the exhaust, we had established a baseline power run on Cobb Tuning Socal’s all wheel drive dyno.  Cobb has one of the most impressive dyno setups that we have ever seen.  Let us walk you through it.
The dyno itself is a Mustang.  The Mustang is an eddy current load type dyno.  Many consider the Mustang better for tuning than an inertial dyno like a Dynojet because it puts a harder and steadier load on the engine.  Mustangs generally read more conservatively than a Dynojet.  Cobb Tuning’s Mustang has a weather station for automated SAE correction and a wide band Air Fuel ratio logging system.
This is the dyno cell air intake.  Air is drawn in from the roof though this baffled duct.  To meet city ordinances the dyno cell intake and exhaust vents hardly emit any noise.  It is hard to hear the dyno in operation either inside our outside the building it is that quiet!
This is the exhaust ducting.  The exhaust is vented out the roof after first passing through a silencer.  It is so effective, you would not know that the Cobb building has a dyno in it from the outside.  The whole dyno cell is lined with perforated steel backed by some sort of sound absorbing fiber.  This make the whole cell like a giant muffler.  The fans move so much air that it feels like a 20 mph gale when the exhaust fans are turned on!  Cobb’s exhaust fans move more air across the front and bottom of the car than most dyno’s main fans!  It is also pretty quiet inside the cell when testing.  When outside the cell, the tested car is hardly audible.

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