for whatever it's worth, and I make this comment within the specific context of the fact that I consider David a friend, having spent a bit of time with him over the years in person, since he lives not too far from me, and I've had arguments on here with Harry (but I'll note I still respect his knowledge and opinions) - in all fairness I think you are over-reacting to Harry's posts. None of us is Shakespeare, and in all sincerity, David, you do come up with a lot of ideas, some of them are more 'doable' or ideal in the real world, others are not so much. That doesn't mean you are an idiot or anything like that, but someimes if we don't bring forward legitimate concerns or forseeable problems, it could end up costing the original poster (or anyone else reading it and considering the same) time and money for a less than ideal result.
Once you start stretching the capacity of the A-series (and within the context of this discussion) to well beyond 1600cc, the biggest hurdle, almost to the complete exclusion of all other concerns, is how much even a very well ported head will be able to support the necessary intake and exhaust flow to keep that engine happy, even at more modest street rpms.
As an example, though the info is certainly well more than 10 years old, NASCAR were running 'basically' the same rules on their superspeedways, save for the fact that the engines had to run a restrictor plate under the carb (I forget if the carb size itself was different too, but that's somewhat irrelevant if the restrictor plate was fitted, and it cuts a hell of a lot of power). It got to the stage that the engines were just starving for air at higher and higher sustained rpms, and they weren't making good volumetric efficiency and the actual 'running' compression ratio was much lower too. And what a few engine builders played with was the fact that engine size was limited, but there was no set minimum. So instead of running the 355ci engines (I think 355 was the limit) they were running shorter stroke engines of maybe 300-330 ci, and due to them being able to get a full cylinder of air/fuel at higher rpm (compared with the larger engine) they actually made more power, and used less fuel to make the same power. It basically made them quicker and also able to go a few more laps (for any given similar run, of course they all still draft other car's slipstreams etc) and it was a winning move. And not too long after that, Nascar then mandated not only a max capacity but also a minimum capacity.
What you are doing with this proposed combination, in a sense, is running a restrictor plate engine (by virtue of a stock head, and remember that even in ported form it'll struggle to feed a decent a15 as well as we'd like, let alone a much bigger one). Ah, but you won't be spinning it as high. That necessarily limits cam duration, which then gives the motor less time to get air in and out for every revolution, but at the same time, as you reduce the duration, due to max safe opening and closing rates of the cams (mostly dictated by lifter footprint size and cam base circle diameter, which aren't too easy to change!) then you are limited much more in terms of lift, not just peak lift, but how long it'll stay at any point beyond mid range lifts (relative term of course). So in practice, there's a hell of a lot of stuff 'choking' the life out of a big engine capacity through an A series head, and even more so an unported one. Ask any historic touring car racer, and as far as engines themselves go (in determining overall performance) 'it's all in the head' so to speak.
I assure you David, and I say this as respectfully as possible without this forum becoming a hug fest, if you put together such a combination, if you added up the costs of going to such large capacity, but stuck with a stock head, a similar amount of money, but priority given to headwork (and you can get gains out of em without needing a full race spec cam mind you, there's lots of room for improvement in the valve guide/bowl/valve seat area before you have to start getting exotic). Anyhoo, that same budget (or even a more modest one) prioritised for the head (and careful cam selection) will in fact get you a much better result.
If you were instead talking of something like an L series, you'd still do head work of course, but it's more than possible to get a very wide powerband and decent top end, basically the whole nine yards, and running a stroked crank combo up to 2.3litres or so. But that is because the heads, esp with some work, are capable of actually feeding a >2 litre engine.
Very generally, esp for a streeter, more capacity pays off, but you have to ensure that the head is actually capable of catering to its needs.
On the carb issue, the wider powerband and better throttle response, i.e. a more flexible all round engine will come from 1 carb throat per intake port, and would be the way I'd lean towards. It would have to be a case of finding the right sized carb (or in the case of dcoe webers or similar, the right choke size) so that it meets it's peak flow demands, but not much more, as any further beyond that and you lose signal strength and velocity, and the mid range becomes less and less crisp, and the overall performance on road is hit hard.
If there happened to be a decent intake manifold (and arguably there are some for mini a series engines, but none that I know of for the datsun a series engine) a largish single SU type carb can produce the goods. But there isn't, so you'd have to make a custom one, and good luck getting it right.
I mentioned in the past the idea of a 4 runner curved intake (inspired by but not 100% identical to toyota k series intakes) and a holley 2 barrel. I'll stand by that option over any modded stock downdraught carb intake manifold that has a single front and rear runner and only branches out right before the ports in a Y shape . I'm not suggesting it'll outgun a twin weber intake, but if done right it'll be about the best you could do as far as a single (but 2 barreled or more) central downdraught carb would. I'd put that above a custom single SU intake, but that's just me. If I find time this summer, I'll do my best to make one (using bits from :
http://www.sonicperformance.com.au/Al ... minium-Half-Donuts/pl.php ) but it's just as likely I'll end up working through!
TO try and put it in simple terms, the idea of a really big motor with a std head, it's a bit like cloning Pharlap (or Seabiscuit for folks in the US) then cutting off one of its legs and being surprised that it doesn't win any races. These aren't personal attacks on you David, it's more a case of pointing out the issues. I can't claim to have done it to datto a series engines, but I've done a fair bit on 'stretched' engines with limited flowing heads (even with porting) and it cost me a fortune to find out that either the whole combo can work with one another optimally, or it won't run half as well as a non stretched engine with money/time focussed on what will really deliver the results.
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