One trick thing we did in the scalars was create a "two-step" rev limiter, to allow us to more consistently launch the car at the drags. Setting the neutral rev limit to 3,500 (along with changing the "transmission type select" to 1, and the "mph to infer neutral for torque limiting" to 0.5) gives us a 3,500-rpm launch limit, until the ECU detects a vehicle speed over 0.5 mph, at which point it goes back to the stock 6,500-rpm limit.
Modified Functions
The only function we modified for the stock Cobra was to set the "tip-in spark advance vs. rpm" to all zeros, in order to keep the ECU from retarding the spark advance on shifts. This modification would not show any power increase on the dyno, but would improve driving performance.
Modified Tables
Tables modified for the stock Cobra tune included the Adaptive Update rate/offset, plus various fuel and spark advance tables.
Bumping up the spark timing...
Bumping up the spark timing is where we can make more power, but we can't be too greedy or the detonation gods will pay us an unwelcome visit. Shown is our tweaked borderline spark table for the Cobra in stock form. We intend to use 94-octane fuel with these values.
The Adaptive Update rate/offset table determines how much time elapses, at a given load and rpm, before LTFT data is updated for each cell. It also determines which cells simply use learned data from other load/rpm points. To keep low load/rpm learning info from being applied at high load/rpm, we set all the table cell values to "4," so each cell does its own learning, and updates its LTFT data after four seconds. This modification does not make more power per se; it's done for safety reasons, and to make sure the tune doesn't corrupt itself later.
For fueling, the stabilized OL fuel table was adjusted to target a 12:1 A/F at high loads for all rpm. Stock, it already called for 12:1 at the higher rpm, so this modification was also not expected to make any more top-end power, but it gave us some additional low-rpm tolerance for spark advance. We knew targeting 12:1 A/F would really have us in the mid-11s for the 10-percent ethanol blend fuel we were using, which is right where we want to be with that fuel, and is plenty safe (Note: In hindsight we realized we should have used straight gasoline for an introductory tuning article, since tuning with 10 percent ethanol fuel requires a bit more knowledge and adds a bit more complexity, but we wanted the 94 octane).
Spark tables were next on the hit list. The first spark table changed was to zero out the tip-in spark retard table, to again prevent any reduction in spark advance during transients. With the tip-in disabled, we also zeroed out the borderline spark adder for A/F ratio, to keep the spark advance more consistent and predictable. Both of these modifications are done to improve driving performance (or for tuning safety), but again are not expected to show anything on the dyno for horsepower.