OK, so for those of you that may be new or have missed the past discussions, the ENTIRE problem with the 2002-2005 I6s with the P10 PCM and no MAF is that once the PCM sees above 1 Bar of pressure at the MAP sensor (its actually the voltage the MAP sensor sends to the PCM, cant remember if its maxed at ~4.7 volts or at 0 volts, think 4.7 though) the PCM throws a code for MAP range error and puts the engine into Reduced Engine Power mode. Which means you cant really do anything.
The hardware part of a turbo setup for the I6 could be done easily, thats not the issue at all. We now even have the Steedspeed turbo manifold that makes it even easier to bolt a turbo up. BUT, here is where the hold up comes. The P10 doesnt have a big enough aftermarket (aka only the GMT360 from 02-05 uses it) to warrant either EFILive or HPTuners to code a custom OS for 2 Bar. Couple that with the complexity of the code that the coder at EFILive says takes forever to track down simple things, trying to make room in an already full flash memory space just simply will never happen.
Also, the P10 being MAF-less meant GM designed a hybrid Speed Density/alpha-N fueling algorithm that is really weird compared to either a true SD or alpha-N system. Basically it means the Spark tables are RPM and MAP referenced while the fueling VE tables are RPM and load referenced. I have yet to figure out how the load value is calculated and until someone does, there is simply no way to do it. And all of the tables would have to be halved in resolution because you need a 2 Bar MAP sensor to run a turbo without blindly guessing your spark and fuel. So you go from like 13 rows down to 4 or 5 (the way GM set the tables up they do not increase linearly).
I looked hard at performing a P12 PCM sway from an 06 I6 as it is the same ECM used in the Cobalt SS/SC and the Ion Redline S/C. But again, there is a difference between an 02-05 BCM and 06-07 BCM (and probably another one for 08-09 as they use another different ECM and TCM) that would not allow an 06 P12 to interface with an 02-05 P10 BCM as far as I know and have been told.
I would love to have someone figure this out, anyone in the Seattle area have an 06 I they'd like to let me borrow for a day?
So everyone who is still reading will ask, what does this all mean?
Simply put, unless you use an aftermarket system to control the spark and fuel after 14.7psi or 1 Bar of pressure, there is no way currently to run boost on an 02-05 I6 using stock GM electronics.
That said, 06-09 4.2L I6s WOULD BE EASY TO DO. Buy the Steedspeed manifold, a turbo, an intercooler (or meth injection), some bigger injectors, the plumbing you'll need, and get a good tuner in the loop (someone local). Ive said this more than a few times now, every single 06-09 I6 could be tuned in a day to a few days by an experienced tuner to run a turbo or supercharger. The PCM (06-07) and the ECM (08-09)s used in them accept boost easily, heck the P12 (06-07) runs it easily on the Colorado I5 turbo and s/c kits and the E67 (08-09) runs the 2009 Cadillac CTS-V 6.2L LSA factory supercharged engine. All the tables are there in the stock OSs for 06-09 trucks, someone needs to take the plunge and go for it.
That is some of the knowledge Ive found out about the P10 after tuning it for 3+ years now, but the likelihood of me ever pursuing it any more for personal reasons is all but done considering my 02 I6 will be gone by year's end in all honesty and my SS with the E67 (hmm look, same ECM as the 08-09 I6s has...) is easy to supercharge.
And as for the fellow that I gave all the above info to, he says he got his 04 I6 running on a 2 Bar MAP sensor and was going back in for the turbo install. Never heard back from him since then, and honestly just getting the MAP sensor in now isnt an issue. Thats simply scaling the spark tables and maybe tweaking the VE a little, not very drastic compared to actually bolting a turbo up and trying to compensate for the added airflow. I know lots of people wont want to even hear me mention it, but I think the next step is seeing if you can use the MSextra code to control the motor's fueling and spark once the stock PCM maxes out (and put a voltage clamp to stop the stock MAP from reporting anything over 14.7psi = no REP light).
To glfredrick, while Fords ECMs might be better on paper for running boost, tuning support for the entire Ford lineup is severely lacking. Between EFILive and HPTuners, GM's ECMs are much more capable. The E67s are the best we have the potential to use (they support both CAN and VPW comms while the E38 does not) but the P12s are a solid choice too (and can control both engine and trans, the E67 you need a T42 as well).