2008 Subaru Impreza WRX STI - Power Check!

Cons
Installation of the exhaust seemed to go without a hitch until it was time to install the main exhaust canister. Our STI has already gone through a makeover and was using an aftermarket Ings body kit. The rear bumper now sitting with a lower stance caused some problems when attempting to install the exhaust canister as the hangers and factory exhaust bushings pushed the unit too far up causing contact with the bumper. We attempted to remedy the solution by using some Cusco extended exhaust bushings but found the harder urethane material used on the Cusco made slipping it on nearly impossible without having to bend or adjust the GReddy exhaust hangers sitting toward the tips of the muffler. This is considered a minor setback for those who plan to sport a body kit but GReddy representatives have ensured us that their SE exhaust has been tested and fit the '08 STI using a factory bumper without any issues.

Dyno Test Results
Adding the GReddy cat-back exhaust system allowed the factory VF48 turbo to breathe more easily as the dyno charted more boost in the midrange and allowed Buenas to add more timing and turn up the boost ever so slightly from its factory 14.8 setting to 18 psi using the AcessPort. A quick reference to boost log showed at 18 psi the boost level was dropping off between 15-16 psi. With additional tuning, the EJ25 powerplant came alive, from 2,350 rpm to 5,350 rpm. A significant gain of 25 whp and 43 lb-ft of torque was recorded from 2,700 to 3,100 rpm. At 4,000 rpm we saw an increase of 15 whp and 22 lb-ft of torque over our previous run.

Product
Downpipe

Installation Time
90 minutes

Cobb Downpipe / Walbro Fuel Pump
Pros
Ask any Subaru owner what product offers the most bang for the buck in terms of power in their EJ-powered machine and nine out of 10 will say replacing the stock downpipe that use restrictive catalysts for an aftermarket setup is ideal. A downpipe is considered a critical component for anyone looking to upgrade to a Stage 2 setup on their vehicle. The Cobb SS downpipe was just the ticket we needed to bring our 08 STI into its final testing phase. Using a cast-designed bell mouth housing, the 3-inch downpipe terminates into a metallic core (200 cell counts) high-flow catalyst with improved efficiency. We could have easily opted for a non-catted downpipe in search of additional horsepower but the thought of killing the ozone layer was too heart wrenching for us to bear. The truth of the matter is living under the strict emission laws of Southern California, we kept to the idea of maintaining at least one catalyst to ward off the toxic fumes the Subaru generates when sitting in traffic or at a stoplight. The downpipe also helped minimize decibel levels which always seem to attract too much attention.

Cons
If it's emissions you're itching to pass, don't rely on the Cobb downpipe to bring you to the promised land. The placement of the metal catalyst found on the Cobb unit won't heat up as quickly as those who place them near the neck of the downpipe to pass emissions, but in terms of power, the Cobb unit promotes less turbulence and will generate more power. A catted downpipe is an alternate solution if the option of using a catless downpipe is too gung ho for your taste.