right now i ahev a 1974 Dodge Dart Swinger with a 318 2bbl. i am looking to upgrade to a 4bbl. Is there a certain one i should get? I also would like to know about intake manifolds and how they affect the cars performance. Any Help?
Thanks  

A 4bbl. will make it a dog.  

A dog, not necessarily.
If you go with a performer intake and a small 4 barrel, such as a 600 cfm vac. secondary holley you will have good overall performance if everything else is up to snuff.
E.g. tuneup, comp, etc.
The Performer intake has power from 0-5000rpm.
The 600 Holley is the perfect size for a 318.
I would also recommend a set of 1 5/8 headman headers to compliment the new induction system.  

I had a 72 Scamp with a 318 2bbl. I swappped to a Performer intake and Edelbrock 600 electric choke. The car picked up quite a bit and throttle response was amazingly great.  I think the trick was the electronic ignition with the orange box and the timing was set on 12 degrees btc at 900 rpm's. I also had a flex fan, a shift kit in the 904, 3.23 gears, 8mm wires, and a dual exhaust with turbo mufflers and no headers. The car ran 10.1 to 10.2 eighth miles at Greer, S.C. on a hot day. I know thats not fast but it was good for a 120,000 mile 318 with stock innards.  

YEA , 318'S ARE STRONG ENGINES , PLEASE DO NOT BE DISCOURAGED BECAUSE OF THE FAD OF THE BIG BLOCK MUSCLE CAR. I HAVE A 318 , WITH DUAL FLOWMASTERS ,  323 REAR , 904 W/O SHIFT KIT , COMPCAM .444 , 4BL EDEL 600 , PERFORMANCE ELECRICAL COMPONENTS , AND AM QUITE HAPPY WITH WHAT IT DOES.  OH YEA , MORE THAN HALF OF THE MUSCLE HEADS WITH BIG BLOCKS DO NOT KNOW WHAT THEIR DOING ANYWAY . SO , HAVE AT IT , BUT MY EXPERIENCE IS THAT THE OVERALL CONFIGURATION IS IMPORTANT , NOT JUST ONE OR TWO PARTS.  

I have a 318 w/ performer intake, holley 600cfm, comp 268/454 cam and 3.55 gears in a duster.  Also has hedman headers and 2" dual exhaust.  Everything else being stock.  How fast do you think this car will run in the 1/8th or 1/4 mile?  Haven't completed the engine yet and I'm just anxious to see how it performs.  I plan on upgrading to a 2.25 exhaust w/ flowmasters eventually.  Any input will be appreciated.