[justav6]

arent we in general discussion forced induction?
anyway... turbo lag is the time it takes for engine rpms to flow exaust out the headers to the turbo, spin the turbine which turns the compressor, then the compressed air to get to the combustion chambers.this all depends on a bunch of factors. most importantly, the volume of space in the headers, turbo, intercooler, combustion chamber, throttle body, turbo, and plumbing. that is why despite what some people think bigger is not always better. actually as far as turbo lag goes the opposite is true. bigger is better for pushing higher amounts of boost (less resistance). also back pressure after the turbo slightly effects lag, but mostly just higher boost levels. a blow of valve arguably slightly reduces turbo lag, but it mostly just increases the life of a turbo, sounds cool, and keeps the engine from stalling if you get off the throttle real quick after pushing high boost levels. this sometimes happens with out a bow off valve because the pressurized air in the intercooler and plumbing has no where to go, so it goes backwards which causes the turbo to spin backwards choking the engine.