hi all just was wondering what does a blow off valve do?

 

If you are talking about a turbo system, it is a valve adjusted to a desired manifold pressure that pop's open when the turbo manifold pressure reaches that desired pressure, it is also used to prevent the system from blowing its self open or overpressuring the cylinders. or getting to much pressure that the fuel vaporizes and causes detonation.

 

i know this is gonna sound stupid but do you need a turbo to have a blow off valve?

 

no question asked is stupid, when trying to gain knowledge.To the best of my knowledge a blow off valve works with a turbo, there may also be one used on superchargers.