3Bs and 2Hs use the throttle plate to develop a pressure differential to give the fuel pump a signal to increase or decrease fuel. It is a Vacume throttle position sensor if you will. I personally don't run a blow off valve and never have, but it's more about how you drive vs total boost. Fast shifting where you are boosting hard then take your foot off the gas pedal abruptly causes surge waves back towards the turbo. I guess you could do it without shifting and just let off the throttle abruptly after accelerating hard. I dont drive that way personally, but if you do it's a good idea to consider one. A clear indicator is to watch your boost gauge and accelerate and let off the throttle and you can see an immediate boost spike. It can go up several lbs. It's not like it will destroy your compressor imediately, but it will fatigue it faster. That being said I know of only one fella who runs one and who ever hears about 3Bs or 2Hs destroying compressors from lack of blow off valves. I think its probably the least of their worriers. It's more semantics I guess.
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