Gen2 Subaru BRZ / Toyota GR86 Dyno Gains Explained

Gen2 Subaru BRZ / Toyota GR86 Dyno Gains Explained

COBB Tuning released support for Gen2 BRZ/GR86 (manual transmission) today. As the calibrator on the project, I’ve been working on this for a bit, and can now share some insight gained during the process. The 50 state legal performance calibration suite includes several new custom features which are exciting, but in this post I want to first discuss the elephant in the room (besides COBB tunes being delivered with an Ecutek dongle for the first time).

Why are we claiming a 2 horsepower gain, while others are claiming 20-25 HP?

The first graph shows 2 baseline runs on the stock tune (green and black), as well as the COBB OTS tune in red (HP) and blue (TQ). You’ll see a 23 HP gain from the first stock baseline pull to the best stock baseline pull, without touching the tune. This gain is created by running multiple power pulls in a row. There is a 25 HP gain if you compare the first baseline pull to the COBB tuned pull, but instead of claiming a 25 HP gain, we are claiming 2. 2 horsepower is the portion gained by the tune by itself on that day, in back to back testing, using the best and most forthcoming baseline run, and a COBB tuned gain we can repeat over and over.

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So how does the car “magically” gain 20+ HP just from doing a few dyno pulls?

While HP and TQ increase quite a bit, engine operation does not change in terms of air/fuel ratio, cam or ignition timing, or throttle opening. All pulls were performed with similar starting coolant and intake air temperatures as well, and in the same gear. The vehicle is at full operating coolant temperature for all runs, but as engine oil, gearbox and differential fluid get even hotter, viscosity decreases, and frictional losses are reduced. This creates an increase in engine output delivered to the wheels.

This behavior was confirmed on 4 different test vehicles on 4 different days, and repeated on a single development vehicle on multiple days. The smallest change observed from 1st to best pull on the stock tune was about 15 HP, mostly due to that test being done on a hot day, and after the vehicle was driven relatively far to get to the dyno, so everything was pretty hot to start. The biggest range in back to back baseline pulls was about 30 HP. During some dyno sessions 3-4 pulls was sufficient to get to peak dyno output, but sometimes 5-6 pulls were required.

I started the development process by performing baseline pulls until the stock tune stopped making more power, so I spotted this my first day with the car. After 2 days of calibration I was fairly confident that 20 HP gains seen online on pump gas were not coming from the tune itself. Still, I’m always open to the possibility I’ve missed something, so I requested we get a third party tune for benchmarking, and see what the dyno had to say.

This second chart shows back to back testing of the 3rd party tune (run 1, red lines), the stock tune (run 2, green lines), and the COBB tune (run 3, blue lines). The 3rd party tune at best made a little less than stock, and caused heavy engine knock not present on the stock or COBB tunes. The 3rd pull on that tune (shown) was its best, and on all other pulls it made considerably less power, while knocking heavily.

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After this test session I felt sufficiently confident that the gains I was creating were what’s feasible on a day to day basis, and my focus turned to compensations to retain as much of that power as possible over varied conditions. That includes accounting for changes in ambient conditions, and heat soak conditions during track use. There were several dyno sessions, track days, and street sessions prior to submitting and ultimately achieving a CARB EO to make this tuning suite 50 state legal, and street or track ready.

While the Gen 1 BRZ/GT86/FRS stock tune left more room for power gains, and you could remove the mid range torque dip via tuning, the FA24 is a more highly tuned engine in stock form. Creating around 230 wheel HP from a naturally aspirated affordable 4 cylinder, with a big bump in torque as well, is a big step forward for this Subaru/Toyota collaboration.

We turned to custom features to really take things up a notch, with race focused 4 phase, 2 mode traction control, progressive water and oil temp based rev limits, and other features that give customers great value.