Just remember that whenever you go to a bigger venturi, the velocity slows down thru it,and at low throttle openings, the transfers do not meter very accurately. Bigger carbs are designed for more cubic inches and or more rpm. Ask yourself how often will you be buzzing it up to 5000. With 3.55s and a 3.09 low-gear, this is about 40mph with 3.23s. At 4000 the formula spits out 32mph. Ask yourself if dragging a 500cfm carb around is worth it for that occasional blast, that in first gear may never even open the secondaries, and if it does, it might only be 10 or 20%, and what kind of metering is that 500 capable of at that throttle opening.
At 4000, the formula spits out 260 cfm at 100% VE. Suppose we give your 256 combo the benefit of the doubt at 80% VE, this is still just 208cfm . You can put a 1000cfm carb on there and it will never pull much more than 208@4000. By 5000 your VE is gonna have dropped considerably,but say it still manages .70Ve. This calculates to 228cfm@5000.So, a factory 230cfm carb will have no problem at 208/228,and you are only gonna be between 4000 and 5000 for 1 or 2 seconds, in first gear running from 32 to 40mph once in a while. But say your combo can pull .75VE at 5000, this is still only 244cfm, and your 230carb is not likely to hit a wall.
But when you hit second is where the problem is. That trans has ratios of 3.09-1.92-1.40-1.00. So the 1-2 split is 62%.. So at the shift into second, the Rs will drop from 5000 to 3100, and yur race is over; There is just no fast way out of that hole for a 225 cuber.Furthermore 4000 with 3.23s will not come up again until 51 mph. So in effect you are sacrificing economy for a 1 to 2 second blast,from 32 to 40mph, every once in a while.
Now, I'm not knocking your 4bbl idea, only the size of it, and the application. If you had an automatic,3.91s and a 3500TC, it would be a whole nuther story.
So, IMO, your combo is begging for a very small spreadbore. One with Super Six sized triple-booster venturies, and metering rods, and an AirValve Secondary, and all rolled into a 350ish cfm size. That 350 is more than enough to feed your 256 equipped 225 combo to 6700@80%VE, by the formula, so it should have no problem at 5000/5200.
But I wouldn't bother to even search for such a thing. If I had to have a 4bbl, I'd just bolt the smallest Q-Jet on there I could find; you know, the ones everybody throws away,lol.
There is a reason the SS system is so popular.
But if you got money to burn, I've always wanted to put a pair of SS's on an aluminum 2x1bbl intake. Those 4 little venturies should fill the bill really nicely.I've never seen it done, but I don't travel in those circles. I wish I had more time in this world to accomplish at least some of my dreams. Maybe I should stayed single,lol.
In any case, keep on keeping on.
But there is a monkey wrench in this story
2bbls, and 4bbls,
are not cfm-rated the same.
And not all manufactures even use the same standards.
So, I'm willing to bet that there is a 4bbl carb out there, that, on the primaries, IS better than a 2bbl, because of the rating difference, and because of the way the engine breaths thru it.
Now if I could just remember the standards; at the moment I'm in a brain-stall.
