It's probably a little too late in the evening to attempt a reply but here goes:
I think what we're looking for is more volume through the injectors as opposed to higher pressure in order to bring the egt down over the broadest rpm range. I'd be inclined to attempt that via reprogramming though I hasten to admit I have ZERO experience with it. BUT, in my simple view and Bernoulli's, lower pressure follows higher flow and I think more fuel flow is the answer to longer engine and header life.
I'm positive DC achieved their CAFE numbers via higher egt (translate leaner fuel flow throughout the rpm range.)
In the doing, I feel they sacrificed engine reliability and longevity.
Question now is, what's the smartest/easiest way to go about reprogrammimg the PCM - have a tuner do it?
(Does anybody know why this 'reply' box jumps around like crazy while you're trying to type?)
AFR is given by the air to fuel ratio per 1 full cycle of a cylinder - that is how much fuel will flow thru the injector while it is open during the intake cycle. The flow is determined by 3 factors: fuel pressure, injector size (nozzle or nozzles) and duty cycle of the injector (higher duty cycle means the injector is opened more).
the fuel pressure is controlled by the fuel pressure regulator and is limited to the pump capacity, so is fuel flow in the rail - higher pressure means less flow given by the pump, has nothing to do with the injector flow at a given pressure
the injector fuel flow is given by the injector size (the hole or holes thru which the fuel escapes while the injector is opened) and related to the fuel pressure - it is directly proportional with the square root of the pressure in the rail (and in the injector body) - what that means is that if for example you want to double the flow given by your injector at a pressure P1 you will need a pressure P2=4*P1 (4 times the pressure to achieve 2 times the flow) - you would need to have twice the flow of fuel if for example you would install a turbo and run 14.7 psi of boost (that is in theory to get to the same AFR as before, in practice you want to run richer and also this is only valid for open loop)
the duty cycle is controlled by the PCM
- in closed loop (when the PCM uses the O2 feedback to adjust the AFR) the PCM adjusts the duty cycle to always target 14.7 AFR, no matter what you do - there is a limit at which the fuel trims will fail to adjust, but that does not mean you'll be able to run richer, will just throw the PCM off and you'll end up with a CEL and the engine running like hell as it won't be able to "learn" the fuel curve.
- in open loop the PCM will operate on a preset fuel table w/o the O2 feedback, that is where you can make a difference by increasing the flow with larger injectors and/or higher fuel pressure - most of the tuners will use injectors to roughly get to the desired flow and an adjustable FPR to fine tune the flow or reprogram the PCM to adjust the duty cycle with the new injectors.
to modify the AFR on an engine using a narrowband O2 the only way is to shift the voltage output so the PCM targets the fake O2 information (thinking is correcting around the 14.7 stoichiometric value when in fact is correcting for a different AFR).
you can also trick the PCM into "thinking" it gets more air than it actually does by shifting the MAP sensor output, this will again only work in open loop but you might achieve open loop sooner by giving the higher voltage output to the PCM at a lower Manifold Absolute Pressure.
You can force the PCM in open loop sooner by reprogramming it and also reprogram the fuel table to achieve a higher AFR in open loop - this is what most of the aftermarket performance chips and programmers do.
