The responses have been in the 600 to 750 range which most would agree is appropriate for a 318. Which you would choose would probably depend on whether you want slightly better street manners or whether max output was the end goal. At least that is the way I see it.
But what I think is the most important issue in carb selection is the calibrations. In any popular size there will be quite a few choices on that. So not every 600 will run the same on your particular combo. Nor will every 750. Your happiness with your final selection may have more to do with the calibrations than the actual size in a primarily street application.
I am not familiar with that cam. Does it have a bumpy idle? If so, I sure wouldn't use one of the CarterBrocks. Their idle and transition circuits are antiquated and second best at the least. And adjusting them is a nightmare. If it is a bumpy idle, I would suggest one of the 4150 Holley style platform carbs that have the 4 corner idle adjustments. And if you need to go inside to tighten the tune, they are much easier to do and to get the parts for.
If the idle is not bumpy, then the best street carb out there today is the Street Demon. Available in 625 and 750 and with different center sections to choose from. They have the best street manners of any carb I have installed. But do not like a bumpy idle. The Street Demon was designed with the help of a retired Carter engineer and take off from where the old ThermoQuads left off. And every carb has both intake patterns, so it will fit your intake. The reason for my preference for the Street Demon is the throttle response. It is just crisper than most any other carb I have ran out of the box.
But let me say again that these carbs work best on mild street engines. They would not be my first choice for hotter or more rodded combos.
That's my
www.youtube.com/watch?v=DPOuEOkazVcwww.youtube.com/watch?v=jN2xbt6Mzdc&t=70s
