Why Carb and non OD a Gen 3?

DionR said
Valid. I think OD is all about getting the engine RPM's into a range where the motor can be more efficient and generally a lower RPM is more efficient. Certainly too low can have a detriment. But aero drag can certainly influence things.

My theory (hope?) is that if the 5.7 is running the same RPM's as it would be in the Challenger, I have the best chance of the greatest efficiency.

Are you taking advantage of the ability with EFI to cut the fuel when costing downhill? I'm not clear on how it works or if it is a 100% fuel cut since the car is going to keep the motor turning, but I've heard it is a nice advantage to EFI. Since the motor is pulling air even with the throttle closed, a carb is still feeding gas while EFI can cut or reduce it under that certain condition.

I have tried some decel fuel cut in the past, but don't recall whether I'm running it now or not. The MS help tips actually suggest against it on a manual car, though I believe that's mostly just because of the "on/off" feeling you can get when you get back on the throttle being jarring to some. An auto soaks up that transition better since it has the converter to damp it out. That being said, I've driven several manual vehicles that still do it like my Viper and motorcycle. You can definitely feel it on the bike because it's a more pronounced deceleration, almost like lightly dragging the brakes. On the Viper it's more of an audio cue. Mine does some pretty good exhaust popping on decel that goes away after a few seconds when the fuel cut kicks in. I think you can just feel the extra decel as well, but I don't think it's quite as pronounced as the bike.

I kind of indirectly have it on the Dart via the fuel map though. The bottom row of my table is something like 15:1 AFR or more, so it's kind of like built in fuel cut to a lesser extent. You can set the cut percentage via the actual decel fuel cut setting though, so I might actually look into playing with that again. I forget all the parameters I have available in the MS, but you basically have settings to control when it kicks in and then how much of a cut you want. So you can have it do a 100% fuel cut if you want. The trigger settings are stuff like what MAP value you need to be under for it to activate and how long you have to be under it before it kicks on. Not sure how other aftermarket EFI systems do it though.

I think your idea of running the engine as close to "as installed" in the Challenger makes good sense though. It was designed to run in some kind of powerband, so makes sense to keep it there if you aren't changing parts on it that would move that around.