The air/fuel ratio is generally not going to change no matter what you're doing with the intake. Forced induction engines typically use richer mixtures because they have serious intake temperature problems. The extra fuel promotes more cooling of the intake charge from the vaporizing of the fuel. Beyond this though there's not a whole lot of difference. You've got to have reasonable mixture for the conditions by the time the mix gets to the cylinders - or you're in trouble. I'm not sure I'd try to do a turbo-blower setup with a carb.
Quote: "dual turbos with the large turbo feeding into the smaller one to spool it faster"
I'm not sure what this means........I've heard of increasing responsiveness with two turbos but it doesn't really work like that. The idea is that a single turbo can't do everything - if it has huge high end flow it's probably going to take a while to get up to speed, if it has good responsiveness at low speed it's probably traded off further up. They're kinda like engines that way - you can't usually have massive lowend torque and a high end screamer.
So what you do is add a few valves so that you can control where the exhaust is going. When you punch it all the exhaust is diverted to the small, quick acting turbo. As the power climbs you quickly run of capacity in the small turbo, but at this point exhaust is going to the big turbo as well and it's coming into it's own.
You can also just use two smaller turbos. Usually ends with more responsiveness but still a lack of high end.
