If (and that's the biggest word in the entire sentence) you could achieve 80% volumetric efficiency (good luck on that one), at 6,500 RPM (and with that camshaft, it will be windmilling at that RPM anyway), a 350 CID engine will only flow 527 CFM, so your 600 carb is plenty enough for what you're doing.
I'm betting you're rarely ever going to screw the motor to the north side of 5,500 RPM and that pulls your flow numbers all the way down to 446 CFM.
Don't guess at things when you can use simple mathematics to come up with a definite answer.
Everyone needs to step back and take a second look at what Lee had to say in his first post -
The problem with an over-sized carb is not "too much gas." The carb will only flow as much gas as the air flow demands. The problem is the venturis will be too large for the air flow that small motor will generate. There won't be enough air velocity through the venturis to allow the carb to properly meter fuel. Your motor will be doggy and unresponsive under normal driving conditions.
Ding, ding, ding, we have a winner!
The amount of fuel your engine will consume is dependent upon several factors, engine RPM being one of the more important numbers. But we need to remember that at a given RPM, air quality comes into play. An engine running in extremely dry air can carry more fuel than the same engine running in a rain forest. At wide open throttle, increased barometric pressure can help get more air moving into the engine and if that air is dry, it can carry more fuel.
At 1,500 RPM, a 350 CID engine can flow a tick more than 120 CFM. You can bolt a 450 CFM carb on, or you can bolt a 1300 CFM carb on, but at 1,500 RPM, either combination will flow about 120 CFM. And that 120 CFM can only carry X amount of fuel, depending on atmospheric conditions.
It's what happens when you stand on it that makes all the difference in the world. A small vacuum secondary carb will snap a pair of small primary blades open, maintaining air flow through the primary boosters, until the air flow requirements get to a point where the secondaries begin to open. A huge, mechanical secondary carb will snap all four throttle blades open, the vacuum signal at the base of the carb will get lost with four boosters trying to sort where the signal went and your head will hit the dash as the motor noses over.
People get confused between naturally-aspirated, gasoline-powered engines and forced induction, nitromethane-powered engines. With your street engine, you're trying to make maximum heat (remembering the cooling capacity limitations of the vehicle), which means using less fuel. With a Top Fuel combination, as long as you can continue to apply more load to the engine, you can continue adding more fuel. When the A/FD combination started regaining popularity in the Alcohol Dragster classes, they just kept running faster and faster, so NHRA decided it was time to slow them down, so the alcohol/blower cars could still be competitive. And NHRA, in their infinite wisdom, added weight to the A/FD cars. More weight meant those guys could load the motor harder, so they started running quicker. But they were stepping further out on the high wire, because trying to run more fuel through the motor means you also have to be more careful about keeping the motor loaded up. Watch a fuel car when it starts to spin the tire. What happens next? It starts putting cylinders out, because without the constant load, it cannot burn the enormous amounts of fuel.
Love 'em or hate 'em, you cannot ignore the HP potential of import cars. They're making incredible amounts of power with those wee motors. And burning tiny amounts of gasoline in the process.
And they're still inefficient, because they still require the use of a cooling system. Heat in the radiator is a waste of fuel energy and until automotive engineers get serious about understanding that fact, we're going to continue wasting fuel. Racers love cool, dry air, because it is capable of carrying more fuel. They take a cylinder charge of air/fuel and ignite it, driving the piston down in the cylinder, exerting leverage through the connecting rod to turn the crank. And then what do they do with that charge of heat they've worked so hard to create? They dump it into a header tube and kiss it good-bye. Think about it, that charge is still hot and still has energy to give up, so why waste it? Why not use that heat to produce steam and add a steam cycle to the engine? The steam will actually help cool the cylinder, which means you can start looking at the elimination of the cooling system. If you can eliminate the cooling system, that means you get rid of the water pump, freeing up more of the engine's power. You are suddenly burning half the fuel as before, which means you are also reducing emissions by half. If you can reduce emissions by that much, you can eliminate a lot of the emission control devices, allowing the engine to make even more power and the vehicle to be lighter. :wall: Why are the auto manufacturers missing the boat on this, whilst wasting time on limited-range electric cars?
