2010 Subaru Impreza WRX STI Special Edition Engine: EJ257 Chassis: GRB Five years ago, Subaru offered the 2010 Impreza WRX STI Special Edition for right around $33,000. With the Subaru exchanging hands from the original owner to the next, used 2010 STI models can be bought for approximately $20,000, leaving plenty of funds for performance upgrades. The biggest hurdle for anyone looking to buy a used STI however, is finding a clean and unmodified car. This is especially difficult since many racing enthusiasts gravitated toward the high-performance model of Subaru’s Impreza WRX offering. For this Quick Tech, we ran a series of tests on a pre-owned STI to increase performance in the most straightforward approach within a reasonable budget.
The Delicious Tuning FlexFuel Kit is a true plug-and-play system, no cutting/splicing or modification is needed – just plug it in and bolt it down and you’re ready to go.
The PartsTo maximize the horsepower and torque output of the factory turbocharged EJ25 engine before adding any power-adding parts, we chose to use an alternative fuel on the Subaru. To accomplish this task, we looked to retune the vehicle with E85 fuel instead of the restrictive 91-octane fuel used by most Californians. With a Delicious Tuning FlexFuel Kit, we could run either 91-octane gasoline or E85 fuel or any mixture of the two without having to determine the ethanol-to-gasoline ratio. This plug-and-play system relies on an inline ethanol content analyzer that measures the ethanol content feeding the fuel rails and relays this data through a dedicated signal to the ECU. The ECU then calculates the correct values based on the exact fuel content entering the engine. The central piece of the tuning equation needed to gain more performance from the STI was a method to access the ECU and calibrate the proper parameters of fuel scaling, ignition timing, cam angle and boost pressure. With the use of flex fuel, an EcuTek ProECU solution was the clear choice. The flex fuel feature on the EcuTek is hardcoded into the tuning software so no custom coding is necessary. This is accomplished by an extra ECU code that was written by EcuTek that is patched into the factory ECU code. The versatility of this section of code is afforded by the RaceROM Feature File, which dynamically adds and removes the custom code as it’s needed. This feature allows tuners to program the best performing tune for each possible fuel used by an input of flex fuel content through a 0-5 volt signal. This integrates seamlessly with the Delicious Tuning FlexFuel Kit, which intercepts vital information through its ethanol content analyzer and factory oxygen sensor. The greater volumetric fuel demand of E85 requires upgrades to the fuel injectors and fuel pump. As such, we opted for Injector Dynamic 1,300 cc/min fuel injectors that feature all stainless internals. The construction of these injectors ensures compatibility with all fuels from straight gasoline to any percentage of ethanol. According to Injector Dynamics, ID1300 injectors are ideal for flex-fuel type tunes since the injectors offer great idle and cruise characteristics regardless of fuel type used. Replacing the in-tank fuel pump with an ethanol-compatible offering was necessary but we received a bit of a surprise when removing what we thought to be the factory pump. Once we accessed the fuel tank and removed the pump, it was in fact not stock but a DeatschWerks DW65c. Looks like the previous owner had a couple things done to this STI before the current owner took possession. This freebie was a welcome upgrade, however, because it’s exactly what we needed, a 265 liter-per-hour pump that is compatible with both gas and ethanol.
The DeatschWerks DW65c in-tank fuel pump is packaged in a compact 65mm body which is perfect when space in the fuel basket is limited.
The TurboXS V2 Catless Downpipe was designed with an undivided bell housing. The result is a free-flowing channel for spent exhaust gasses exiting the turbo.
EcuTek Additional FeaturesThe EcuTek tuning software is a powerful tool that allows more than simply accessing the ECU’s fuel and ignition tables. Built into the software are a host of additional features. We tapped into the following customization tools on this STI.
1) Flat Foot ShiftingTo minimize time between gearshifts, the EcuTek software allows for flat foot shifting (full throttle shifting). This feature holds the engine speed at the RPM when the clutch pedal is depressed in between shifts. The result is faster shifts that don’t require the driver to remove their foot from the accelerator. Additionally, with flat foot shifting there is no drop in RPMs between gears.
2) Launch ControlOne of the biggest performance advantages that the Subaru platform offers over other vehicles is its Symmetrical All-Wheel Drive system. To get the most out of AWD launches, we used the EcuTek to program the built-in launch control function. With the vehicle stationary and in first gear, the driver can depress the accelerator all the way to the floor and the EcuTek will hold engine speed at a user- selected RPM. The launch RPM can be adjusted in realtime with the factory cruise control buttons.
3) Map SwitchingWhile many enthusiasts only drive at two speeds, stop and go, some opt to drive more conservatively at times. The EcuTek software allows for the tuner to customize the factory STI SI Drive selector to deliver a low and high boost map. On our test vehicle, Bill Knose programmed the S# (Sport Sharp) option with slightly more boost and an aggressive throttle mapping that gives a little extra response in throttle input.
The Subaru’s factory controls were used to access some of the EcuTek software’s additional features including a high boost map which is ideally used when the tank is topped off with E85.
Baseline[pullquote]253.95 WHP @ 6,200 RPM
244.47 lb-ft @ 4,300 RPM
14.98 psi @ 3,650 RPM[/pullquote] We strapped the STI onto DSPORT’s Dynojet 424xLC2 Linx AWD Dynamometer in factory form with 91-octane gas in the tank. As we connected the RPM pickup and vacuum line from the dyno to the car we noticed that the STI had yet another aftermarket component. This time we found a GrimmSpeed 3-Port Electronic Boost Solenoid. The 3-port boost solenoid allows for high-resolution boost control and provides steady boost levels throughout the RPM range. Again, we were happy to have this upgrade on the car but were concerned that the previous owner may have abused the car. Baseline pulls confirmed that the EJ257 engine was alive and well with a healthy 253.95 whp at 6,230 RPM and 244.47 lb-ft of torque at 4,330 RPM at the factory boost level of 14.98 psi.
Test 1: Delicious Tuning Flex Fuel Kit & Injector Dynamics ID1300 Injectors
Test 2: TurboXS Catless V2 Downpipe & GT Catback Exhaust
Bottom LineWith just one power-adding component, we were able to extract substantial gains from the EJ257 engine. The addition of flex fuel allowed for the versatility in tuning on either 91-octane gas and E85. In return, the race-gas-like characteristics of the ethanol blend fuel opened up the door for more power production through ignition timing, fuel enrichment, boost pressure and camshaft control. The maximum power numbers broke through the 300-horsepower mark to 331.86 whp, while torque skyrocketed to 379.66 lb-ft. The maximum incremental gains were huge as well with an additional 108.97 whp and 149.74 lb-ft of torque occurring at times throughout the powerband. In analyzing the cost to performance gains, we found that the conversion to flex fuel added up to less than $2,000 and delivered an additional 51.81hp and 68.87 lb-ft of torque to the wheels. Looking forward, this setup pushed the factory VF48 turbocharger near its limit, the next step would be to address this bottleneck with a higher-capacity unit. Stay tuned.
|HP Level||HP Increase||% Increase||Total|
|Test 1: Flex Fuel Conversion||305.76 WHP||+51.81||20.4%||51.81|
|Test 2: Exhaust System||331.86 WHP||+26.10||8.54%||+77.91|
|* * * * *|
|FINAL POWER||331.86 WHP||–||30.68%||77.91|
|Delicious Tuning Flex Fuel Kit (DT_FFBT_V01)||$595.00|
|EcuTek ProECU Programming License||$345.00|
|Injector Dynamics ID13000 Fuel Injectors (1300.48.11.WRX.4)||$900.00|
|TurboXS Catless V2 Downpipe (WS08-DP)||$508.00|
|TurboXS GT Catback Exhaust (STI08-CBE)||$849.00|
|DSPORT Street Price:||$2,557.60 – 2,877.30|