I am still in the theory stage...
The PCM's programming seems to match the Chrysler thought process, which dictates that the engine cannot be made to perform at a higher level than stock. They so much as admitted this in the pre-production press when they announced that there would be Stage I and Stage II Mopar performance kits made available for the GT in the future. Stage I is rumored to be a PCM upgrade. Chrysler took the route of lowering the compression so the boost would run on the upper edge, just to lessen the chance of the owner being able to muster more performance by playing with boost levels.
With that in mind, the PCM's job is to de-rate the potential of the engine to perform. When the powerband it reached, the boost is tapered off. It is the sole purpose of the PCM, through the various sensors and safeguard circuits to reduce the performance of any add-on, mod or assembly, until the performance falls back in the curve that the PCM is programmed for.
I found that after a few days with the MBC on, when I took it off, the PCM would not allow boost higher than 10 pounds. I reset the PCM by removing the battery terminal for 30 seconds, and then the boost would reach above the 10 pound mark.
Like others, I have found that you need to be above 2500 RPM (actually around 2300 RPM), and you need to put the pedal to the floor and hold it there for any siginificant boost to occur. In the 5 speed, being in too high of a gear and then flooring it does cause the engine to "lug" and is prone to cause all sorts of sensor-invoked changes in running parameters to be introduced.
If the PCM's programming is bulletproof in respect to responding to what the sensor's tell it, then we need to teach the sensor's to embellish the truth. This is why I theorize that the TIP can be easily made to tell the PCM that boost pressure is less than it actually is. I feel that the TIP, and maybe the MAP are the main sensors that cause the wastegate solenoid to be engaged prematurely (at least prematurely for the performance we expect). The easiest approach would be to fool them into reporting less boost pressure than is actually present. If that worked, then the MBC could be set for high of 14 and low of 10 to 11, and the TIP sensor could be fooled in reporting the pressure it sees at the low; say 11 pounds pressure to be 7 pounds.
If padding the TIP works, then we could remove the MBC, reset the PCM and take some readings of what the stock system tries to lower pressure to in each gear at specified RPM. With that info, the MBC can be reinstalled, PCM reset again, the TIP padded to report similar pressure readings, when the actual pressure is what we desire.
The problem that would need to be considered is what would keep the boost pressure from exceeding 14 when the TIP is under reporting it.
Questions for the PCM Programming would be does the TIP report only when the PCM is looking to vent boost, leaving the high boost reporting to the MAP? If this is so, fooling the TIP for vent pressure would not affect the ability of the PCM to tell the wastegate to lower high end pressure above the 14 pound threshold.
From what I am reading on the SRT forum, there is definately a major difference in the PCM programming between the GT and the SRT. They are reporting some really high boost levels and few errors.
The GT was apparently programmed to allow the customer to have performance, only as an option that the Stealership could sell to you. Pay as you play plan..
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