First, anyone who states: "Just set your AFR for stoichiometric" has clearly NEVER tuned a car.
I've never heard or read that. Anybody who says such a thing should be avoided
. Having said that, there are/have been factory produced cars that do run constant 14.7:1 AFRs, even turbo'd 1s.
I'll appeal to the carburetor guys first. You all know that once you set your idle mixture screws to approximately 2 turns out and get the car to temperature you then adjust the idle mixture for maximum vaccum (or minimum MAP). And of course the end result is a RICH idle! Not an AFR of 14.7!
Lots of engines prefer to idle with a rich mixture, and is largely effected by camshaft overlap. Sequential injection systems typically allow leaner idle mixtures as there is less tendancy for the fuel to fall out of the minor amounts of air flowing past the valves.
Second, there's the problem of heat build up. Exhaust Gas Temperatures (EGT) should be in the range of 1300 to 1500 degrees. At WOT and AFR (Air/Fuel Ratio) can easily exceed this, and therefore requires richer ratios (more like 12.5)
EGTs are effected by more than just AFRs. Ignition timing has a huge effect, less advance = higher EGTs.
Which brings me to a point I once made in a prior thread: I predict that the future of EFI OEM and aftermarket systems will include built-in accelerometers, EGT sensors as well as the standard Wide Band Oxygen sensor. This will allow the computer to go well beyond closed-loop mode! It will allow the computer to actually adjust the AFR table!
Autotuning abillities have in use by the various aftermarket computer makers here in Australia for some years now. Some of them are apparently very, very good.
Factory systems of the last 15-20 years are far more advanced than a lot of people realise and comparing a simple system like the megasquirt to just about any factory system is very ambitious.
Simply quoting (and I know you haven't done this) maximum power an ENGINE made with brand xxx computer is really stupid. Tuning for max power is the easy part, and, as you have alluded to, it's all the parts between an idling engine and max power that is the fun part.
Please, don't get me wrong, I'm not having a go at you, and I'm deffinately not some 'expert', but I have studied (via the 'net) the workings of the Nissan ECCS type engine management systems and read as much as I can from as many creditable sources as I can find.
Some exstra reading:
Stuff about tuning
More stuff about tuning
('tho about Nissan ECUs, the complexity for an old system is quite amazing)
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I also reccomend Greg Gordons book on Supercharging.