how much antifreeze do I need to buy and how much water do I mix in it so that my car doesn't over heat? i have mostly water in it now but it's getting really cold out and I need to get antifreeze in it because i still don't have a winter beater car and my camaro is my dd.

 

3 gallons of premixed, or two gallons of 100% and a gallon of distilled water.

 

You should also drain your block, not just the rad. There are plugs on both sides of the block that allow you to drain each side. Simply draining the rad won't drain the block. If you just try putting a premix into the rad, it will be too weak once it mixes with the water that's still in the block. Putting just 100% into the rad is a guess because you don't know how much water is actually in the block.

With the block drained, I'd recommend 3 gallons of 100%. Start with 1 gallon of antifreeze then 1 gallon of water. Another gallon of antifreeze then another gallon of water. If the cooling system isn't completely filled by now, put as much of the third gallon of antifreeze in. If needed, top up with no more than 1 gallon of water. Run the engine with the heater on to circulate the mixture. It may take a while to get all the air out. The engine should be run long enough to get the temperature up to open the thermostat.

Doing it this way, you're going to get a minimum of a 50/50 mix. If your cooling system is full part way through either jug, you'll have a slightly higher mixture which won't hurt anything.