Side note: the compressor goes into aerodynamic stall, but the shaft doesn't actually rotate backwards. That would really be an extreme case. If it were instrumented and steady state (think turbine engine instead of turbo), we could induce surge by adding air pressure to the compressor outlet until it spills over to the inlet side. We'd know it was surging from the sound (unique and bad) or just from watching high speed pressure data on the compressor outlet side. It isn't subtle.... steady... slowly increase with your inbleed air.... increasing.... tiny bit of noise.... BAM Pressure drops as close to instantaneously as possible, usually will try to recover, and repeat and a pretty high frequency. This is a pic of the VERY FIRST TRACE of surge. Baby surge. Infant surge. When it's bad, it's WAY WORSE than this pic shows. We were sneaking up on surge in this pic with the goal of "don't blow up this one of a kind motor in a multi-million dollar test cell".
It's actually a lot of fun, but your eyes get bleary and when you shout "SURGE!!!" it's all assholes and elbows with your team trying to pull a several hundred thousand dollar motor out of surge. The actual surge line depends on temperature, altitude, humidity, load, etc. In a car add RPM to that for extra fun. This is why you want to keep your aftermarket turbos running aftermarket boost and aftermarket parts as far away from that as possible, and an easy, cheap, simple to implement way is to put the right spring in (ahem.... black for Tial, orange for Turbosmart), and run a dedicated line.
I'll keep saying this until I'm blue in the face. Now, a couple caveats.
1: If you run a stiffer spring you'll vent later in the off-throttle situation, and less air will vent before the valve closes. The BOV will do a worse job resultantly. The BOV will be less responsive.
2: If you have huge laggy turbos, this may make you think you're better off, as you're not waiting (as many) weeks for them to build boost back up. This is a good indicator you may have bit off more turbo that you have a palate for with respect to responsiveness. It'll help the situation, with respect to lag, but not the situation with surge. Good news is some of the dyno queen turbos aren't going to surge any time soon as you'll have moved the map (i.e. engine load/rpm) long past where they'd surge because, well, they're so damned slow to actually get up to speed. If you're a highway roll monster with NLS, disregard, you chose your poison, run it! Daily driver? Ugh. Pass.
3: I won't speak for the other guys, but if you run our turbos, please run the correct damned spring. Especially the GC family is very responsive, enjoy that, run a lighter spring like we say, get some good longevity out of them, have fun not waiting months for your turbos to make torque when you're just trying to pass some slow-poke in a minivan.
Correct to prevent boost spike or flutter but we are talking about engine response which I was saying the quarter inch line would help more. So when someone says engine response that is very diff from bov response and if the bov is open and you floor the car the engine will be sucking air correct so that would pull air and have vac on the top of the bov, this coupled with turbos that were still spinning and were venting so have positive pressure would still pushing on the bottom of the bov and venting boost then as the spring overcomes the vac on top and boost on bottom it would create a surge in power and airflow as the boost now enters the manifold. I ask questions not cause lack of knowledge or understanding but because theirs always someone smarter so being condescending isnt wise especially when you misunderstood and made a general statement that isnt accurate. Lighter isnt always better it's a goldilocks situations. I really do genuinely like you but sometimes you need to hop off the horse usually it's when a competing product is better but in this case it's because people hypothesized that the Christian gospel wasnt accurate , maybe I'm on a bad mood but if you dont want to repeat or explain yourself write a book dont post on a forum. I never spoke more than 3 to 4lbs more than I'm targeting if that breaks my turbo than im glad to get it off my car as far as the pressure wave in throttle issue just saying.
1: If you floor the car, the first thing that happens before the witch doctors conjure their boost spell, is throttle opens all the way. This equalizes charge pipe and manifold pressure and..... you gets zee bov to close comrade! No problems!
2: Sorry you read that post as condescending. It's more bemused. This is why I write with funny accents from time to time. I'm guessing you took your cranky pills. I am willing to hug it out, but any more than 3 ass pats... things will get weird.
3: The rest of your post was some solid griping from you, which IIRC, is fairly rare. I appreciate that both high horse and christian gospel were both used as criticisms lol. Solid. That said...it's just BOV's, worst case if you don't get it or are getting frustrated, just shoot me an email with what your setup is (doesn't even have to be vargas turbos!) and ask me what spring to use. I'll point you in the right direction and all will be well. If you don't like it, you're out $20 or whatever a spring costs and you learned to never trust Chris@VTT again. I have an ex-wife that would have gladly paid $20 to write me off all those years ago. xoxo
Chris
