Hello, L81'ers, a newbie checking in here...
A couple of thoughts on the issue of "whether my carb can keep up with my modified motor".
As long as the primaries of the E4ME can flow enough air by themselves to fill the engine volume at a rev level where you would consider the engine to be lightly loaded, say, cruising the freeway at 65 or 70 mph in top gear, then the CCC system will keep the A/F mix near optimal. After that, it's exactly what is posted above: you have to have your secondaries manually tuned to provide the right mixture.
A 383 operating at 2500 rpm, assuming 100% cylinder filling efficiency and ignoring heat losses, would ingest 277 cfm of air. Do the primaries of the E4ME flow that much? I don't know, but I think so. There's a trivia question for the FAQs!
As you continue to push the pedal, exposing the top of the carb to vacuum, the air all flows through the primaries until you reach the their limit of flow, more or less. Then, continuing to seek the path of least resistance, the vacuum opens the air valve above the primaries, and the air flow through the secondaries starts to pull fuel past the rods and into the venturis to be mixed with air.
It's pretty easy to see how it works at small throttle openings, where the primaries easily handle the flow, and it's also easy to see how it works at WOT, where the computer is bypassed, the primaries go to full rich, and both the primaries and secondaries are flowing near their limit. But the in between part gets a little fuzzy (to me, anyway).
In the original 350 L81, as you go from idle to WOT, slowly pressing down on the pedal, which would happen first: the secondaries would open due to vacuum, or the TPS would trigger the computer to be bypassed and the primaries would go full rich? I know they both happen, but which one is first?
It seems obvious to me that as you increase engine displacement, you increase the rate at which you expose the carb to vacuum by opening the throttle. In other words, since a 383 is about 10% bigger than a 350, you would be exposing the air valve over the secondaries to 10% more vacuum at any given degree of throttle opening. That tells me the secondaries will be opening sooner, i.e., at a smaller thottle opening, than they would on the 350. The question is, will the primaries already be at full rich, or not? Since they depend on the throttle opening as indicated by the TPS, the primaries will not go to full rich any sooner on a 383 than on a 350.
It seems possible that there could be a period there in which the secondaries were open but the computer was controlling the primaries, and that period would be bigger as the engine gets bigger. (Maybe that's common knowledgeto the rest of you guys, but I haven't thought about it before. Thanks for letting me ramble!
) If that's true, then I expect there is some very real performance to be gained on the 383 or 406 by tuning secondaries, both in terms of the rods for mixture, and the air valve spring tension. And I'm thinking the only way to know is with the Air/Fuel meter on a dyno or dragstrip, checking to see if you are getting periods of leanness or richness as you accelerate under load.
If the above is all true as it relates to displacement changes, then wouldn't it also be true for other changes that increase the air through-put of the engine, such as bigger cams, better heads, better exhaust, etc.?
btw: I'm running a Summit crate engine, 355ci, rated at 330hp/390tq, with the E4ME carb and CCC system installed just as on the original L81, but with a Performer intake, headers, and dual exhaust. And it hauls.
I'm glad I'm not the only person telling the world that the E4ME is not garbage. 
