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2008 Subaru Impreza WRX STI - Power Check!

Dynamometer Model: HB Speed Dynomite Dynamometer

Scott Tsuneishi
Dec 17, 2008 SHARE
Turp_0812_01_z+2008_subaru_impreza_wrx_sti+dyno Photo 1/14   |   2008 Subaru Impreza WRX STI - Power Check!

AccessPort Tuning: Jon Buenas

Baseline
Pros
The newly designed '08 Subaru Impreza STI, powered by the infamous 2.5L boxer engine is rated at a factory 305 hp and 290 lb-ft of torque. The '08 model continues the Subaru legacy as its rally proven symmetrical all-wheel-drive system and turbocharged powerplant have been a successfully lethal combination in the world of automotive performance.

Turp_0812_02_z+2008_subaru_impreza_wrx_sti+baseline_dyno_results Photo 2/14   |   Baseline Dyno Results
223 WHP 250 TQ

Cons
It's a known fact that the new era of automobiles sold in today's market have become more technologically advanced into both electronics and engine efficiency. The news is a promising forecast for the average daily commuter but a nightmare for those looking to increase horsepower by simply slapping on a few bolt-on parts. The '07- '08 Subarus (and some 06 WRXs) were tuned from the factory to pass strict emissions testing, often sacrificing the true potential of the EJ25 engine. "They run stoichiometric air/fuel ratios (14.7:1) through peak boost and to about 4,000 rpm, which is great for fuel economy but BAD for power and driveability," HB Speed owner and tuner Jon Buenas says. The '07-'08 ECUs also have multiple timing tables that, upon certain situations, add, subtract, or even multiply the timing values the motor runs. There are tables within the factory ECU that can add to themselves and then add to the total timing (bad). There are also timing floors where the total timing value cannot go below a certain amount, which are also considered bad. What does this all mean to a Subaru owner looking to bolt on a few go-fast parts? "If the vehicle is not properly tuned, the ECU can take the tuners intended timing value (lets say 11) degrees at peak torque and if it so sees fit (using knock feedback and other algorithms) add 8-10 degrees (effectively running 19-20 degrees). The problem is the ECU is not quite fast enough to pull out that timing if it knocks hard (which it would) and eventually would blow the motor up," Buenas says.

Turp_0812_03_z+2008_subaru_impreza_wrx_sti+accessport Photo 3/14   |   Cobb Tuning Accessport Tuned Baseline (Stage 1)

Dyno Test Results
With numerous horror stories spread throughout the community of Subaru '07-'08 STI models with piston ringland problems, and most recently '08 turbocharged Subarus being recalled for engine knocking noise, we took special precautions in running our baseline dyno pull to get our preliminary numbers. The '08 STI rolled the dyno to a tune of 223 whp and 250 lb-ft of torque. Note the power numbers we list throughout this test are given in wheel horsepower and not to be mistaken for flywheel rated power.

Product
AccessPort unit, user guide, USB cable, OBD-II connector, software CD

Tune And Remap Ecu Time
Full day process

Turp_0812_04_z+2008_subaru_impreza_wrx_sti+cobb_tuning_accessport_tuned_baseline_dyno Photo 4/14   |   Cobb Tuning Accessport Tuned Baseline (Stage 1)
257 WHP 277 TQ

Cobb Accessport
Pros
Cobb Tuning recently released the newest version of their AccessPort to work in conjunction with the '08 STI. The AccessPort is a simple to use hand-held device that enables Subaru owners to plug the controller into the factory OBD-II port. Within minutes, one of the pre-installed performance maps or a custom map can be easily uploaded into the vehicles ECU to alter and optimize air/fuel ratio, ignition timing, and boost. Added features when using the ACCessPORT include the ability to monitor fuel economy, troubleshoot ecu codes, estimate 0-to-60 and quarter-mile times, and even monitor real-time data as you drive around town.

ConsSimply bolting parts on the '07-'08 STI and neglecting to run the proper ECU tune can spell disaster for your engine. Many Subaru tuners recommend a reflash or stand-alone fuel management system for the ECU, prior to making any modifications as many stock '07-'08 turbocharged Subaru's have been known to blow up on occasion. Keep in mind as you begin to modify your engine that each part will change the factory tuned ignition maps and air/fuel ratio, some more than others.

Turp_0812_05_z+2008_subaru_impreza_wrx_sti+injen_cold_air_intake Photo 5/14   |   Injen Cold-Air Intake

Dyno Test Results
Carefully monitoring the vehicles air/fuel ratio and ignition maps with a laptop, Buenas made a few dyno pulls as he modified the factory ECU's maps in order to optimize and achieve a safer ECU map to work with without having to worry about grenading the engine. The tuning had worked its magic on the STI as dyno figures show a smoother graph from its initial pull to redline while netting us with a gain of 34 whp and 27 lb-ft of torque

Product
Intake, Ea nano-fiber dry filter, 2 3/4 straight hose, fenderwell heat shield, powerbands, 18-inch foam rubber trim, m6 vibra-mount, m6 flange nut, m6x12mm hex head bolt, fender washers, m4 x10mm bolts, instructions

Installation Time
20 minutes

Turp_0812_06_z+2008_subaru_impreza_wrx_sti+injen_cold_air_intake_dyno Photo 6/14   |   Injen Cold-Air Intake
270 WHP 293 TQ

Injen Intake
ProsWith the '08 STI still new to the market, Injen Technology was able to pull a few strings and ship their newly developed intake for our vehicle testing purposes. Using what they refer to as MR Technology "the world's first tuned air intake system", Injen representative's state the intake was designed to run factory safe air/fuel ratios for optimal performance. Within 20 minutes we were able to remove the factory intake and replace it with the new Injen unit. We liked the fact that the simple, yet effective design of the pipe was engineered to use a fender head shield and foam rubber trim to reduce intake temperatures.

Cons
Vehicles using a MAF, including the Subaru, rely on the MAF curve to be calibrated to the intake on the car. Diameter changes to the pipe, including aftermarket air filters, can drastically affect the tune and air/fuel ratio on the motor. As you recall with our '08 STI, we decided to reflash the ECU with a tuned map before installing any aftermarket parts. Using an Innovative air/fuel monitor, we found when adding the intake that the unit had leaned out the engine by approximately 0.75 air fuel ratio. Our goals from the first initial pull on the vehicle was to test and tune every part installed to ensure the maximum potential each product offered and give our readers a realistic idea of what to expect.

Turp_0812_08_z+2008_subaru_impreza_wrx_sti+midpipe Photo 7/14   |   2008 Subaru Impreza WRX STI - Power Check!

Dyno Test Results
The Injen intake with tuning didn't disappoint as it picked up both horsepower and torque from its initial pull till redline. The dyno graph revealed a gain of 20 lb-ft of torque at 3,200 rpm. Promising numbers were recorded at 3,750 rpm as a pickup of 15 hp and 20 lb-ft of torque were recorded over our previous tuned baseline run. A solid gain of 15-20 whp and 10-17 lb-ft of torque was obtained from 4,350 rpm to 6,600 rpm as the graph neared redlines.

Product
Exhaust, midpipe, bolts, nuts, gasket flange

Installation Time
70 minutes

Turp_0812_07_z+2008_subaru_impreza_wrx_sti+rear_view Photo 8/14   |   2008 Subaru Impreza WRX STI - Power Check!

Greedy Se Exhaust
Pros

GReddy stepped up to the plate and offered to test their Spectrum Elite (SE) exhaust system on the '08 STI as the exhaust was a soon-to-be-released unit during our time of testing. The SE system uses a 70mm diameter piping, which terminates into their free-flowing exhaust canister. Flame-treated tips give the SE exhaust its own unique look while adding some added flair to the STI. Along with its aggressive appearance, the exhaust has been designed to emit a legal 95dBA decibel rating, which ensures cops won't harass you on the streets.

Turp_0812_09_z+2008_subaru_impreza_wrx_sti+greddy_se_exhaust Photo 9/14   |   Greddy SE (Spectrum Elite) Exhaust

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.

Turp_0812_10_z+2008_subaru_impreza_wrx_sti+greddy_se_exhaust_dyno Photo 10/14   |   Greddy SE (Spectrum Elite) Exhaust
274 WHP 312 TQ

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

Turp_0812_11_z+2008_subaru_impreza_wrx_sti+cobb_tuning_3in_catted_downpipe Photo 11/14   |   Cobb Tuning 3-inch Catted Downpipe

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.

Turp_0812_14_z+2008_subaru_impreza_wrx_sti+cobb_tuning_downpipe_dyno Photo 12/14   |   Cobb Tuning SS 3-inch Catted Downpipe
285 WHP 352 TQ

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.

Turp_0812_12_z+2008_subaru_impreza_wrx_sti+fuel_pump_install Photo 13/14   |   2008 Subaru Impreza WRX STI - Power Check!

Dyno Test Results
Before our final session was to begin on the rollers, the factory fuel pump was replaced with a Walbro 255lph pump. The installation of this pump requires some serious modifications to the plastic housing that surrounds the unit and is considered very labor intensive. Luckily for us, HB Speed had the experience and knows how to tackle the installment in a short time period. With the newly installed Cobb downpipe in place, Buenas made use of the AcessPort and remapped the ECU with a more aggressive AVCS and timing map while turning up the boost to 20 psi. Buenas stays using an aftermarket downpipe allows him to tune more aggressively whereas using the factory downpipe would limit any tuners ability to properly extract horsepower. The Cobb downpipe along with tuning offered a significant horsepower and torque increase over our exhaust run. At lower rpm the dyno recorded a gain of 60 lb-ft of torque from 2,500 to 2,850 rpm. A consistent gain of 25 whp was seen from 2,500 rpm to 3,600 rpm, while the largest margin of gain was a whopping 27 whp and 45 lb-ft of torque at 3,250 rpm.

Turp_0812_13_z+2008_subaru_impreza_wrx_sti+rear_view Photo 14/14   |   2008 Subaru Impreza WRX STI - Power Check!

Conclusion
What began as a baseline dyno run of 223 whp and 250 ft-lb of torque was quickly revamped with our final run of 285 whp and 352 ft-lb of torque. A gain of 62 whp and 102 lb-ft of torque turned this '08 STI into a whole new rocketship. These were impressive numbers that were made possible with the help of proper tuning and someone knowledgeable to tune the new '08 STI. We can't stress enough how important tuning is when looking to create horsepower because our STI is living proof that this new breed of Subarus have definite power potential.

PARTS MSRP
Cobb Tuning AcessPort $695.00
Injen MR Series cold-air intake $374.64
GReddy SE ({{{Spectrum}}} Elite) exhaust $669.00
Cobb Tuning SS 3-inch catted downpipe $595.00
Walbro 255lph high-output fuel pump $105.00
MSRP TOTAL $ 2,438.64

HB Speed
714.378.DYNO (3966)
www.hbspeed.com

Cobb Tuning
801.713.0035
www.cobbtuning.com

Injen Technology
909.839.0706
www.injen.com

GReddy Performance Products
949.588.8300
www.greddy.com

South Coast Subaru Performance
(Walbro pump)
714.689.2103
www.southcoastsubaru.com

RESULTS
  BASELINE COBB ACCESSPORT TUNED BASELINE STAGE 1 INJEN MR COLD-AIR INTAKE GREDDY SPECTRUM ELITE EXHAUST COBB SS 3-INCH CATTED DOWNPIPE
PEAK HP
223 @ 5,350 rpm 257 @5,400 rpm 270 @ 5,450 rpm 274 @ 5,450 rpm 285 @5,520 rpm
PEAK TQ
250 @ 4,330 rpm 277 @ 4,{{{200}}} rpm 293 @ 3,7500 rpm 312 @ 3,750 rpm 352 @ 5,520 rpm
FINAL POWER
GAINS
Baseline +34 WHP
+ 27 TQ
+13 WHP
+16 TQ
+4 WHP
+19 TQ
+11 WHP
+40 TQ

Total Gains
+62 WHP
+102 TQ

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By Scott Tsuneishi
247 Articles

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