[arghx7]

The long period of closed loop (i.e. near stoichiometric) is for fuel economy and CO emissions. You'll see more and more of that as time goes on, especially on engines that have been designed to handle high exhaust temps (water-cooled exhaust manifold).

I have a comment about the seemingly large fuel trims on a stock car.

During engine development, the MAF scaling and a lot of other tables were set using what's called "mean spec" parts. You know how when you buy aftermarket fuel injectors from certain vendors, they give you "flow matched" sets? It's a similar idea. Take the tolerance band of the part, and find one that's in the middle of the range. These are special parts right from the supplier. It includes front and rear o2 sensor, MAF sensor, injectors, etc. So what happens is, on production parts things start to drift. As long as they are within some specification, and the various long term (engine dyno & vehicle) tests confirm, they're ok.

One more thing to consider is the level of friction on the vehicle. The vehicle itself isn't "broken in" until 4000 miles. What I mean by that is 4000 miles on the vehicle is required for certification testing. In that time you decrease friction all over the vehicle. Even on an engine dyno, as the number of hours increases, you can see an increase in output and might be able to measure a decrease in friction mean effective pressure.

One implication of break-in is in the tuning of the electronic throttle for idle behavior. Electronic throttle typically has various learning values, similar to fuel trims. The idle air trims change as the friction decreases on the engine. The feed-forward idle airflow lookup tables need to reflect this.

Just think about what you would do if you had to tune 10s of thousands of engines that you'll never physically see and haven't even been built yet.