To keep accelerating (with any life) a carb has to have say 25% more cfm available than needed at a specific RPM. so at 4200 at 100% is 386 cfm + 25% = 483 cfm so a 500 cfm carb would be kind of minimum to get to 5000 with some decent pull!
Just my



600 eddies and holleys work good on a 318!