Doug, you would be far better off running 390's or 465's over running a 600 or larger carburetor. You would pick up performance overall. I have Run 390's and 465's on my 302 Windsor like I said for over 40 years. They have run great all the way to 8200 RPM. I used to run the car quite a bit at Willow Springs back in the day. Here is the best article I've ever seen on 2x4 setups and they have a lot of pictures including the Dual Dominator setup on a couple of Trans-Am cars. They also have a picture of the Cobra 2x4 Carter intake. The Duel Dominator setup uses an IR intake which I have along with a pair of NOS carburetors and the offset distributor that it requires. Randy and I have known each other for over 40 years and he is one of the most knowledgeable people on Ford engines especially small blocks that I know
https://www.hotrod.com/articles/5-tips-dual-quad-carburetion-success/
Sincerely, Roy Richards
One of the nice things with this setup is that there are so many possible combinations.
Most likely for me, I'm not done experimenting?
I initially set up the high rise with two converted 4180 ('85 Ford GT) carbs. Those are generically a "600 cfm" carb but with the annular discharge boosters probably closer to 565 or so.
I had tried a pair of 1850s with the high rise and the 4180s were much better.
The article is very interesting but doesn't deal with a small block application at all. There is much specific cross over information that does apply.
Don't forget that on the T/A manifold, the carb application eventually arrived at 660 center pumpers with mechanical linkages. On a 289, if that isn't over carburation for the street, I'm not sure what is?
It doesn't touch why the dual dominators work on a 302 either. That simply is because the manifold is an IR design and that is as close to running Weber 48 IDA's as anything.
The Holley "carb size demand chart" is for a 180 manifold with a center plenum. IR manifolds need to be dealt with by the individual flow of the port.
Interestingly enough, I am having the same issue of getting the engine to idle down from 1250 and I haven't looked at the secondary settings. A great reminder!
When I switched over to the T/A, I also had some technical maintenance issues and wound up switching to 1.7 shaft rockers, and AFR 185 heads (which immediately bent all the push rods).
I had the 3300 and 3301 here restored by Holley and they needed to be wet checked and run in so...guess what?
Now all I can do is in an attempt to maintain some semblance of sanity, which probably went out the window for me 30 or 40 years ago, and drive the thing enough to get an idea of where to go with this set up?
Don't forget that I am also screwing around with the advance, both the initial, rate of advance and total? The aluminum heads are throwing some major curve balls and I'm still searching for cause and effect in several cases.
Not to change the subject and compare t-bone steaks with apples but I learned from my Audi TT turbo that running lower boost at 20 psi with a different curve makes much more power then it did at 28 psi and it doesn't blow up the intercooler!
I don't doubt that there may be better carb combinations and that the much smaller carbs yield more area under the curve but my impression was that the smaller carbs (so far) made TOO MUCH torque for my gearing with the Doug Nash 4+1.
So so far I have gone through the 4180's, the 1850's, and the 3300's. I have not tried the 465's and I just looked at my electric bill for the month and it is clear that I won't be for some time.
VERY fortunately for me, I don't have to run a head to head match up against you and Randy. I'd probably screw it up anyway and blow out the clutch or blow a tire?
Strangely enough but probably predictably, I've run into a scenario where my 2.5 mile test circuit is just too short to accurately test these combinations. I really need probably days or weeks of time on a road course like VIR to accurately make decisions on which is the best combination. I'm probably way over my head with driving ability since the car is really at a T/A level already and I need someone like Miles, Donahue or maybe Possi to drive the car and tell me what it needs?
I guess since these "issues" aren't likely to happen with "standard improvements" and I suppose that indicates some level of success on my part? It probably also indicates the accuracy of the adage of "be careful of what you wish for because sometimes you get it!"
You see, for me, these solutions just create issues in other areas? Adult diapers aren't cheap and my friendly local cops don't argue, they just stare and back away. The NYS troopers however are the "Gestapo".
I do appreciate these types of discussions since it benefits me as well as others with information that only insane folks would be able to obtain in a nut house if we were all locked up together?
However, there are others here that are also hopelessly infected and this info could help prevent nurses chasing them with big hypos filled with sedatives, so carry on.
The true answer is something that I really heard from Randy, "I just got you into the game, you need to figure out the details".
It's now like Force complaining to Coyle that the car doesn't make enough power and Coyle shooting back, "hey, sometimes you need to get the monkey to pedal the car". In my case it's only me.
Also, I acknowledge that ultimately I may be forced to decide which carbs are best simply for simple "streetability" of the entire car, and simply put, I just don't know where that is yet, but inevitably I will... eventually. Check. Acknowledged!