My name is Braden and I am an R&D Calibration Specialist at COBB. I am working on the Focus ST, mostly because I begged Trey to let me.
I bought my own ST as my daily driver just a few weeks ago. It’s a great car and should prove to be a good tuner ride in the future. I come from owning just about every turbo Subaru there was, with my last one being a 2004 WRX wagon that was making just over 500whp on our Mustang AWD dyno.
We’ve been doing a lot of development on our STs and have learned some interesting things that I thought I would share::
Stock R&D Findings
From the factory, our cars are torque monsters. They generate 280lb-ft of torque at the wheels (on our Mustang AWD dyno) from 2,000rpm to 4,000rpm. This gives a LOT of punch off the line and makes them really fun when you jump on the throttle (to the detriment of wheel hop and sad engine mounts). Unfortunately, this power level can be rather inconsistent. We have noticed that engine performance is extremely sensitive to Engine Coolant Temperature (ECT), Charge Air Temperature (CAT), Intake Air Temperature (IAT), and Catalytic Converter Temperature (CCT). When these temperatures increase, the ECU decreases power delivery. There are several factory components that can be improved upon to better handle this engine’s peak power output and keep temperatures in check.
Intake R&D Results (Stage1)
Welcome to Speed Density, or, in other words, this is not a MAZDASPEED3! The factory air metering system uses three MAP (Manifold Absolute Pressure) sensors and does not incorporate the MAF (Mass Air Flow) sensors found on many of today’s modern vehicles. What this means for us enthusiasts is that the ECU will be less sensitive to common modifications such as intake upgrades. A MAF sensor meters air mass by detecting voltage changes across a heated wire element in the intake tract. This is a very precise calibration, and altering the air filter or intake system can introduce turbulence or change the airflow pattern across the sensor and affect the sensor’s output. This is why vehicles with MAF sensors typically require a retune when the intake is upgraded, which recalibrates the MAF sensor so that it can accurately meter air mass with the new intake. A MAP sensor works purely on air pressure, and does not have the same calibration concerns with respect to changes in airflow or turbulence, which makes making changes to the intake tract less of an issue.
Interestingly, what we have found is that the OEM airbox is well designed and is not a restriction to airflow. We experimented with removing the lid of the airbox, and what we found is that the engine ingests hot air drawn from the engine bay, predictably resulting in higher IAT, translating into a reduction in power. The factory airbox must remain sealed to deliver optimal performance. Aftermarket upgrades that take advantage of the way this well designed factory system draws in cool air from outside the engine bay will produce the most consistent gains in power.
The factory MAP sensor elbow appears to be sized adequately to support power gains up to what the stock turbo is capable of producing. The OEM turbo inlet hose is made of many corrugated pieces, various bends, and pancakes that do a great job of reducing intake tract noise, but do so at the expense of smooth airflow into the turbo. Replacing the OEM turbo inlet hose with a smooth section will optimize airflow into the turbo and allow audible feedback from the turbo and bypass valve.
Power gains with these upgrades will be minimal on their own, but paired with a recalibration of the ECU – there are gains to be had here.
Intake + Catback R&D Results (Stage1+)
The OEM catback is a one piece design similar to first generation 2007-2009 MAZDASPEED3. It can be removed by cutting the rear section off and unbolting the remaining front section, or by lowering the rear sub frame for access to remove the entire catback intact. The OEM muffler and resonator are HUGE for a reason; to reduce the enormous sound output of this vehicle.
Our initial catback exhaust designs with minimal components resulted in dB levels comparable to a loud rock concert! After numerous configurations, we’ve found the perfect combination for this car.
The catback alone produced minimal gains on the dyno, but does help to decreases exhaust back pressure. This results in more consistent top-end performance by reducing temperatures from run-to-run. The exhaust note is incredible and unique, unlike any hot-hatch I’ve heard before it. Combined with the intake, our cars are almost fully optimized to take advantage of tuning.
Intake+Turbo-Back Exhaust R&D Results (Stage2)
This is the jam. The OEM downpipe inhibits flow, creates back-pressure, and increases temperatures that are ultimately responsible for top-end power inconsistency. There is also an oversized flex-section designed to allow for the astounding amount of engine movement designed into the engine mounts. So much so, that we’ve had the engine into the firewall during hard shifts.
Replacing this component will play a crucial role in eventually making big power safely and consistently. Due to the reduction in back-pressure with our downpipe, we did see that temperatures are reduced across the board. This results in more consistent power delivery and a slight bump in top-end power when untuned (~15-20whp). When tuned – big.
The ECU in the Ford Focus ST uses torque targets to hit consistent power output in various conditions. This means that the ECU tries to have the engine make the same power in 50 degree weather that it does in 90 degree weather so that the car performs consistently. The ECU does its job so well that despite freeing up restrictions in the intake and exhaust systems, the power gains are not very significant. Adding bolt-on products without tuning will be insignificant. You really need to modify the torque targets to make this one scream.