I'm using the end of a broom stick! (seriously!)

On MFI cars the problem with dump valves is that it releases air that has already gone through the metering head where the mixture is set.

So the metering head injects a certain amount of fuel for the air it has detected going passed it. If you "dump" some of that air through a dump valve, you're mixture will be too rich when going back on throttle. In my experience however, the effect is a lot smaller than what people make of it.

I've run my car with and without dump valve and to be honest, I couldn't really notice any difference. So it's really up to you. If you like the noise they make, go for it, if not, get rid of it.

Just make sure the dump valve used is a twin piston one and that the car idles steadily.