Sorry man, but you are waaay off. It has nothing to do with air/fuel, What you are referring to is air/fuel ratio. In the instance of compression ratio, it's all about how much compression of the air and fuel in the cylinder is occuring in each combustion cycle. picture it like this:
you have a certain volumetric capacity for a cylinder bore when the piston is at it's lowest point, this is represented by the number 1. see the pic below:
Now, when the piston is at the top of the bore, that volume of air/fuel mixture is compressed by the piston at the top of the cylinder, in the case of the 2ZZ engine, it is compressed by 11.5 times the full volume of the cylinder. Again, see the pic below for an idea of what this means:
So, when you are figuring out how much you are compressing the a/f mixture in the cylinder for a given application, you represent it by putting how much the cylinder volume is compressed, followed by a colon, and the number 1. so it is notated for engineers as 11.5:1 (or when saying what you want your mechanic or engine builder to do to your motor, you tell them, "eleven-point-five to one")
it is possible to have an overbore (for example: 11.5:1 could be changed to 11.5:1.5, but this would mean the overall cylinder bore would be lengthened over stock, however, since this is impossible in most engines without some serious retooling, you usually don't see this, in all automotive performance applications, the last number in the compression ratio notation will always be 1.
the compression ratio is important because the more you compress the air/fuel mixture prior to igniting it, the more force the resulting explosion (yes, the mixture is exploding every time your plugs fire) the more force will be generated when the mixture combusts.
However, there is a fine line between too much, and too little compression. If you put the A/F mixture under too much pressure, it can detonate without a spark (pre-detonation) and this is bad, and where knocks and pings come from. too much compression under forced induction, such as a turbo or supercharger, can have the same result, which is why the boosted guys run lower compression (8.5:1 is common on turbo 2ZZ celicas)
Running too high of a compression can damage connecting rods, piston tops, valves, piston rings, and may even crack your cylinder walls, so knowing the basics of engine building, or knowing someone who does, is essential when upping the pressure in the cylinders.
However, on a N/A car, higher compression can be benificial. TRD
Japan makes a 13:1 compression piston set for the 2ZZ, but please note, you must run 98 octane fuel or higher to prevent pre-detonation from occuring (higher octane fuel is more stable, and can be compressed more before detonating on it's own.
Hope this clears it up for you