For 2023 we decided to purchase a new Subaru WRX for research and development purposes. The goal and purpose of purchasing this vehicle is to learn as much as we can about the new FA24 turbo platform and its related tuning systems.
Enter 2023 WRX base trim 6-speed manual in Ceramic White. We landed on the “base” trim package for a few reasons but primarily because fewer bells and whistles generally mean less overall weight. Since we plan to modify just about every system in this car there was no need for any of the added features and cost of the other trim levels.
First thing after a very short (less than recommended) break-in time was to strap the car down to our DynoJet 424xLC Linx chassis dynamometer and get a baseline of the car. For consistency and to establish a good baseline we measured 5 full throttle pulls from 2000rpm to the factory redline of 6000rpm. Of these 5 pulls the second was the highest however subsequent pulls showed little to no drop in power. This is an important note going forward as the car clearly requires 2 back to back pulls after any modification to achieve full power. For this reason all future test comparisons will be made on the 2nd pull in a series if possible. All numbers will be posted with SAE weather correction and an SAE smoothing factor of 5.
Due to mechanical configuration we unfortunately cannot measure manifold pressure on the dyno without modifying the vehicle for a boost pickup. For this reason most boost numbers will have to come from vehicle datalogger instead of dyno boost pickup.
In totally stock form (including stock wheels and tires) the car made a respectable 263.89whp and 258.98 ftlb of torque. The car peeks 13psi of boost pressure and tapers off to around 12 by redline. Contrary to initial reports the stock calibration on the vehicle uses "open loop" fueling at wide open throttle, this means that no short term air fuel ratio feedbacks are applied while the vehicle is under high load. This means that modifications that increase airflow will not be compensated for through fueling corrections. Luckily this vehicle is equipped with digital mass airflow meter which is extremely accurate and well calibrated on the stock airbox. This means that while no fuel trim corrections are happening at WOT the vehicle is calculating higher airflows and injecting more fuel for those increases. By this logic, you can modify basically anything to do with airflow as long as you leave the stock airbox intact.
Sadly at the time of purchase of our 2023 WRX there was no custom tuning support from Cobb. We made the decision to add a few modifications to the car anyways under the logic that the MAF could properly calculate the fueling and load required for the increases in airflow. We were correct. After adding the Extreme Turbo Systems catback exhaust and top mount intercooler the vehicle ran as good as ever with a little more power. Past 4000rpm we saw power and torque increases for a total yield of 268.51whp and 265.52tq. What was interesting was the nearly identical torque and power below 4000rpm, we will get into this in a future blog but it turns out the boost control system is quite good at hitting and maintaining it's targets and the factory exhaust is very good stock but is slightly restrictive past that 4000rpm mark hence the horsepower gain. There was no noticable difference in air fuel ratio which confirmed that even though there was no "closed loop" (vehicle makes short term fuel changes) fueling at WOT the MAF was doing it's job correctly calculating airflow. One thing to note is at the time we added the power upgrades we also did a number of cosmetic upgrades which included a performance wheel and tire package from Enkei and Falken. These tires have considerably higher rolling resistance and may actually reduce the overall measured horsepower and torque slightly on the dyno. Even with this the car still picked up power. In general I try and test things in as close to similar conditions as possible but sometimes due to time constraints (ie we had a show to take the car to) we cannot.
Parts installed at this time:
- Extreme Turbo Systems (ETS) Catback Exhaust
- Extreme Turbo Systems (ETS) Top Mount Intercooler
- Extreme Turbo Systems (ETS) Upper and Lower Radiator Hoses
- PREracing Front License Plate Delete
- APR Carbon Fiber Radiator Cooling Plate
- APR Carbon Fiber Subaru Front Wind Splitter
- APR Carbon Fiber Alternator Cover
- APR Carbon Fiber Front Bumper Canards
- APR Carbon Fiber GTC-300 Adjustable Wing
- Seibon MB-Style Carbon Fiber Side Skirts
- Enkei NT03RR 17x8 et35 5x114.3 Wheels
- Falken Azenis RT660 XL 255/40R17 Tires
Dyno graphs, first is baseline, second is baseline vs installed parts
