Thursday, July 16, 2009

Tuning Half-Done...

Cobb Tuning looked at our slightly funky ECU (see previous blog post), did a collective shrug ("Weird, we've never seen that before."), and reflashed it back to its initial state. Then when the ECU came back I realized that my AccessPort was still "married" to the ECU in its previous state -- so I couldn't use the AccessPort until THAT was also reflashed. Anyway, a couple of weeks and several postal shipments later, the electronics were all ready to go, and we strapped the car to the dyno on a very hot and humid July day. Initial results were promising, but I was having some trouble making the car reach my desired boost level. I realized that the newest Subaru ECUs have several temperature compensation tables related to boost levels.

Basically, after the intake temperature exceeds 104 degrees F, the boost targets and duty
cycles are all reduced, and the hotter the intake temps get, the lower the boost targets get. According to my logs the ambient temperature at the dyno was 102 F, and the intake temperature on our car was exceeding 135 degrees F -- that would explain why the car was seeking 19 psi instead of 21 psi. The only way I could keep tuning at my target boost levels was to zero out all the temperature-triggered safety features, but I felt it best to leave those in place. I decided to continue the tuning process in the morning when the ambient temperature was below 102.

Here are my initial results from the first half of the tuning process. Since the turbo is larger than stock, there is some spool penalty -- note how the red power line is above the blue line between 2600 and around 3500. But where the stock turbo is reaching its peak torque, the larger Tomei turbo is just getting started, and the torque and power exceed the stock numbers from that point on.

Once the air temps are cooler and I can depend on the car making the boost pressures I specify, I'll get back to work
-- I hope to be able to show some additional power on my next update.

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