Our 300 cid pickup is running 11.9s with two tiny 2Vs totaling an equivalent 4V flow of 340 cfm @ 1.5"hg.
But do you really have just 1.5" of vacuum pulled at WOT? As manifold vacuum rises the 'real' CFM flowing through the carb goes above the bench mark rating . . . no?
I would be really surprised if there was even 1.5" at 5000. And that is the problem with overcarbureting. If your carb is too big the intake depression will be too low to create a good signal in the venturiis, leading to lean and erratic fuel delivery. You could bolt a toilet to the intake that would flow huge CFM, but the intake vacuum would be nil (and resultant velocity too slow) causing the car to fall on its face.
One of the biggest reasons EFI will produce more power than a carb is EFI does not need any intake Delta P to work. The high pressure in the fuel rail "squirts" the correct amount of fuel in the cylinder. No venturii restriction in the intake is necessary for proper function.
