Okey dokey, here goes...

First I will start with the bottom line. If you like the 04+, the first power modification you should do is a software change. Ecutek and the Cobb AP both involve modifying the base programming of the ecu by reflashing it.


Now to get geeky
You really should not add an external form of boost control to the 04+'s, at least without doing the above; but then it would be redundant.

Here is the problem explained:

Closed loop = ecu looks at sensors like throttle position sensor (tps), mass airflow sensor (maf), manifold absolute pressure (map), knock sensor, coolant temp, exhaust gas temp (egt), intake air temps (iat), knock sensor, rpm's, creates a "calculated load", blah blah blah. Most important - the o2 sensor. Then it looks up tables and maps to try to correct the air\fuel ratio, making it lambda (14.7 which is optimum for catalytic converter efficiancy, READ: lean) This action creates a fuel trim memory that is both constantly referenced, updated, and adjusted - first in the short term (st fuel trim), then when patterns are repeated, long term (lt fuel trim).

Open loop = ecu looks at important stuff like map, maf, iat, rpm's, knock (until 5-6k ish rpm's where it is disabled), but not the 02. Then it looks up some different maps, Think of a toilet flushing. This is what the ecu does in factory open loop trim. It dumps fuel trying to make it as rich as possible to keep things safe safe safe.

Ok, got that?

The 02+03's basically look at the tps for transitions. 55% tps will usually flip the ecu into open loop. The 04's look for that, but need to verify some more parameters, thus taking a longer time to make the flip over to safe afr's.

Cool?

When you add boost control, like electronic or manual (ebc, mbc); superceding the ecu, you run into the situation called part throtlle\full boost (ptfb). Just like it says, you push all that air, but only dump a little fuel because you are in closed loop. People that do this with the 02-03 modify their throttle input (driving style) to keep it in open loop whenever in boost. It gets 'er dun though! Lots of people run great numbers with a mbc. It works for them.

04's are a different story. The transition input and flip time depend on a few more parameters, and there is an intentional delay (for emission purposes of course!) before going open loop. So it isn't really difficult to go way lean; with excessivley happy timing one day- kaplow!

So, yeah, the bottom line is you should refer to the first paragraph about bottom lines with the EM on the 04; even super flowing exhausts sometimes monkey with them! Saving a little longer for smart EM will make for a happier, better running rex.

Not as well known to me- I believe suspension top hats are different so spring interchangability is questionable.

I'm running out of beer... Can't hold out any longer..........
No seriously, sorry to break it down so hard ,, good luck with your pick!

later, x