confused on the sbc

hello everyone, im new to the forumn and need some advice. I live in the uk and just imported a 240z with a 327 chevy v8 in it, and to be honest i have no knowledge on the sbc engine at all. But its a 327 block date of manufacture is 1962, the inlet manifold number says it is a 350-400 cubic inch manifold date around 1969 got the oil filler neck on, would this help with horse power having bigger manifold or not, also it has the edelbrock 4 bbl 600cfm carburator on runs ok but im confused as to how this carb works, it would appear that it runs on the front 2 ports during normal driving then when you excelerate hard the rear 2 ports also come on line, thing is the rear 2 ports only come on when excelerator is nearly all the way down, but it could be adapted to come on sooner or would this not work due to say the power curve comming on to soon bogging the engine down, also the rear 2 ports have a flap on them with weights on that move freely what is the purpose of this any advice would be appreciated regards 240zchevy v8

I think it would be advisable to find some good publications and study up on the engine. Tens of thousands of articles and books have been written on the sbc engine since it's introduction with the 1955 model.
You have a vacuum secondary carb which means the back 2 or (secondary) throttle plates open at higher engine demand. There are also mechanical secondary carbs that open the secondarys with just the linkage position, usually start opening around half throttle. Those top butterflies are connected to the secondary metering valves I believe so as the air rushing past opens the plate, it also lets in more fuel.
You have to decide what you want the engine to do before you start looking for better performance.

By removing the secondary vacuum butterflies the secondary throttle plates are controlled by the secondary linkage. Doing this will an adverse effect on fuel consumption and I wouldn't recommend doing it on a vehicle running an automatic transmission.

Here's the owner's manual on your carb. It should help you understand the operation of it......
http://www.edelbrock.com/automotive_...ers_manual.pdf

The weighted flaps on the secondaries open as the the air flow to the engine increases. Thats so you don't get a bog when the secondaries open. You can take it out if you want to know, in the seat of your pants, what the acceleration feels like. You will know when the secondaries open.