Here’s one:

To arrive at the most appropriate carburetor choice, there's a basic formula: engine displacement multiplied by maximum rpm divided by 3,456. For example: a typical 355ci small-block—a 0.030-over rebuild—with a 6,000-rpm max engine speed would work well with a 616-cfm carb ((355 x 6,000) 3,456 = 616.32).

Or this: Carburetor CFM Calculator - Find Your Carb Size

 

Here’s one:

To arrive at the most appropriate carburetor choice, there's a basic formula: engine displacement multiplied by maximum rpm divided by 3,456. For example: a typical 355ci small-block—a 0.030-over rebuild—with a 6,000-rpm max engine speed would work well with a 616-cfm carb ((355 x 6,000) 3,456 = 616.32).

Or this: Carburetor CFM Calculator - Find Your Carb Size

I make it 687 the calc asks for efficiency, i'm assuming that is VE, which I think would be highly relevant but I don't have that figure and why would they send a brand new dynoed engine with way too bigger carb. I assume appropriate carb, means best all round street manners and fuel efficiency.

 

Keep in mind that a 850 DP is similar in flow to a 1050 HP.

 

does this carb on the car still have power valves,if so one may be bad

 

also the idle feed restictors are not on topor outside the carb.if you put wire in to any that are on top of carb it gets richer

 

I didn't put them in the top, i put them in the metering blocks to restrict the fuel, I may have used the wrong words. If the PV was faulty wouldn't it backfire.

 

i have seen power valve leak fuel to the engine from the gaskets and the diaphragm,also how many turns out are the idle screws

 

99% of people told me an 830 was too big for al my 406 10.5:1 hydraulic motor.
The Summit site has a calculator that told me it should be 827cfm. It's probably the formula SMjR mentioned.