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2015+ WRX STI Mod Guide

We did some testing on a 2020 STI here at our shop and wanted to share the results with you guys! This was a completely stock EJ25 STI and we did 3 stages of modifications from stock and kept track of the results to compare. All of these results are uncorrected numbers which are about 25% lower than you would expect to see on a Dynojet dyno or our “Shootout” numbers.

Our starting point was completely stock. With no tuning, no modifications, and with 91 octane fuel.

This vehicle made 214.9 HP and 218 TQ on our Dyno at 15psi.

Below you find the information of our findings along with dynographs for comparison. If you have any questions about building your 2015+ WRX STI, give us a call (763) 316-5882.

Stage 1 vs Stock

This included the Cobb Accessport, Grimmspeed 3port Boost Controller and Grimmspeed Intake. We performed a custom tune to 18psi on 93oct.

This stage we made 232.5 HP and 263.1 TQ on our dyno. We saw a 18 HP or 8% increase in peak power and 45 FT LB or 21% increase in peak torque. We were able to make 20-30 HP over stock throughout the whole powerband.

*Note – This stage and all our other stages get rid of the dangerous lean condition that happens until about 4000rpm on the stock tune. This lean condition can cause broken ringlands.

Stage 2 vs Stock

This stage includes all the parts of Stage 1 with the addition of a Grimmspeed Downpipe and external wastegated uppipe. We performed a custom tune to 19psi on 91oct.

This stage made 249.2 HP and 280.7 TQ. We saw a 34 HP or 16% increase in peak power and 63 FT LB or 29% increase in peak torque. We were able to gain 49 HP at 4100rpm tapering to 34 HP increase at 5500rpm. With 93oct you can expect an additional 5-10 hp over 91oct.

*Note – At this stage if you want to run an aftermarket intake combined with an aftermarket downpipe, we recommend installing one of the following parts to help with mechanical boost creep. Mechanical Boost creep can happen in the colder months and we can not tune around it. One option is to let the boost creep happen and install larger fuel injectors and fuel pump, so we do not max out the stock fuel system. Another benefit of upgrading the injectors gives you the ability to run E85/flex fuel in the future. The other options are to install the Stock Intake, install an external wastegated uppipe, or port the internal wastegate on the stock turbo. All of these make it so we can control the boost in the winter months and not max out the stock fuel system. Not doing one of these with aftermarket intake and downpipe will at times have a dangerous lean condition above 6000rpms.

Stage 3 vs Stock

This stage includes all the stage 2 mods plus the addition of Injector Dynamics 1050x Fuel Injectors, Cobb Flex Fuel Kit, Cobb Fuel Pressure Sensor Kit, Cobb Fuel Pressure Regulator Kit, and AEM 320lph Fuel Pump. We performed a custom tune to 22psi on E85.

This stage made 299 HP and 353 TQ. We saw a 85 HP or 40% increase in peak power and 135 FT LB or 62% in peak torque. We picked up about 100 HP in the 3250-5000rpm range tapering down to 80 HP increase at 6500rpm

*Note – All of our 08+ STI Tunes include Boost Select. Boost Select allows you to control boost levels via the SI-Drive Knob. Intelligent [I] is the lowest boost level (wastegate pressure), Sport [S] is the medium boost level, and Sport Sharp [S#] is the highest boost level.

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(763) 316-5882