whats the difference between a 2 barrel and a 4 barrel holley

[UK-Barracuda]

this is goin to make me sound so stupid, but please can some one tell me the difference between a 2 barrel and a 4 barrel holley, on a 318 v8

also which are better,

cheers

[Chryco Psycho]

the basics are 2 or bbls & air flow volume , the Holley 2 bbls can be a s big as 500 Cfm & the 4 bbls start at 570 , the catch here is that the 2& 4 bbl are not flow tested the same way so the comparison is not as equal as it seems 
generally 4 bbls give better milage & power as 2 smaller bbls in a 4 bbl carb are more efficient at mixing fuel Than 2 larger bbls in a 2 bbl carb the downside is you need to swap the intake to a 318 4 bbl intake which can be difficult to locate , the older Eddy LD4B is one of the best choices for a 4bbl 318 intake

[hooD]

This is not a Holley carb.  It is not for a 318 either.  But the picture will show you the size of the primary barrels vs the size of the secondary barrels. 

carter thermoquad for 340

[Chryco Psycho]

most 4 bbls have more equal sized borres , the TQ is a spread bore carb with very small primary bores

[Roppa440]

A "barrel" is American slang for a venturi or choke.
A "two Barrel" is a twin venturi or twin choke carburetor. Both barrels open at the same time. They are small and are usually used on the smaller engines.

A 4 barrel carb has one half the same as the 2 barrel. This is called the "Primary" side. The other half is called the "Secondary" side and it does not start to open until the primary side has opened part way. It may be opened mechanically (on a carb called a "Double Pumper") or by means of a vacuum signal from the intake (called a "Vacuum Secondary Carb").

Adding a bigger carb does not make your engine more powerful. Any engine needs the correct sized carb for its size and performance level. Performance is decided by the size of the engine, the cylinder head flow, and the valve timing. The only time a bigger carb will make more power is when the original carb was too small to start with.

[Super Blue 72]

Some of the 2 barrel Holley carbs look very similar to a 4 barrel except that the rear barrles or venturies will not be there on a 2 barrel.  When I was younger I would see a 2 barrel and think it was a 4 barrel.  With different carbs a 2 barrel will be more obvious, like a 2 barrel Solex, Mikuni, Weber, Rochester, etc...

A 2 barrel Holley, notice no rear venturies:


A 4 barrel Holley, notice that from the front, it looks like a 2 barrelwith the fuel bowl set up:

[Super Blue 72]

BTW, if you have a pic of the engine of the Barracuda we can tell you what we think you have. 

[Roppa440]

And here are 3x two barrel carbs called a "Six Pack".

[UK-Barracuda]

cheers guys,

here's a pic of the engine, not the best as i took it on my phone, when my dad gets it home, ill get few more of the engine.

[Super Blue 72]

UK, do you have a pic without the air cleaner on?  The quality of the phone pic is good enough, IMO.