No, without a turbo, there is no blow off valve. However, if you really wanted to, they have fake blow off valves for sale. These mimic the sound of a blow off valve. It would be an absolute waste of money, but hey, it's your money.
The turbo increases the pressure of the air entering the engine, so that there is more oxygen inside the cylinder when the spark plug ignites it - and the piston is pushed down with more force...
Amazingly pointless. The blow off valve is there to release intake pressure if you have the turbo spinning and then go off the throttle suddenly. If you haven't got a turbo there's no intake pressure...