[My427stang]

I personally think that going too small on a dual plane is giving up a ton of mid and upper end without gaining anything down low. In the very least try both, dont just go small, you have a serious motor

A single plane with a large plenum may be a different story, easy to overcarb and they can be a bit fussier down low, but a dual plane needs as much airflow as it can get, any one cylinder is pulling from a plenum fed by only 1/2 of the carb, and airflow at the booster is not an issue with 480+ cid and the RPM port and plenum size.

I run a 1000HP on my 489, I run a/c when its hot out and in 5th its an overall 2.36:1 final drive. I run it around town like a stocker, or will spin it up and let it roar with no downside.

I had a 770 on it for a while diagnosing an issue that turned out to be ignition-related, and it was like I was pulling a parachute with no gain in low end drivability or mileage at all. I didnt dyno, but if you told me I lost 50 hp I'd believe it, heck maybe more, it was amazing. I am not stretching the truth at all. A white knuckle ride, repeated before and after the 770 was noticeably tired above 4500 with the small carb, and both were tuned as well as I could dial them in.

Remember, hot 427's in the day ran at least 2 600's if not 715's, and you are adding 55 cubes and much more efficient airflow! How can a 780, perfect for a mild CJ motor be good for a light car and a 482?

Vizard's old rule of thumb is 2 cfm per cid, recently he has published some other discussions of carburetor sizing on a dual plane that blows away the small size belief, even on small blocks

Try a 780 if you are concerned, but for laughs, beg or borrow an 850, or even better a 1000 from HP or Quick Fuel, and do a back to back street run or even better dyno tests, you'll see. That motor needs air, more stroke, more bore, much advanced heads and intake design, why choke it?