Since you're a beginner, I'll go easy on you. You want a bypass valve, or a recirculating blow off valve. Neither will be loud like you want. But that's because the loud ones are vent to atmosphere type. This creates unregulated airflow through your intake system. You do NOT want this, if you want the car to run well.If you're after top performance, you'll have to forgo some of the show and sound that most people want. Most things that people want, are actually pretty pointless, or even harmful to the car.Another key thing to keep in mind, is to match up your parts. For example, if you go with a small turbo, which will match the engine well, you do not need a gigantic front mount intercooler. It's totally pointless. It will just create a loss of PSI and lag.You also don't need a 4 inch exhaust, as another example.Make sure you address your pistons/compression ratio as well. Most N/A engines have a pretty high compression, and you really don't want that for a turbo car.Not saying you're going to get these things, just food for thought.The turbo is never actually "off", there's just times where it's not increasing airflow, just kind of idling. If you turned it off, you'd have all kinds of problems. Think of it like wanting to turn off your wheels.From the cars I've driven with and without turbos, it's really not that big of a difference in fuel mileage. Until you drive around while boosting all the time. Did that a few times, and fuel economy sucks. But drive reasonable, and it's not bad.