Tonight I replaced my Turbo XS RFL BOV with a Blitz SS BOV. I love the sound of the Turbo XS BOV, but the Blitz will bolt on to the flange on my intercooler piping.

Anyway, I am not crazy about the sound of the Blitz BOV. It is much deeper in tone and quieter than the Turbo XS. The Turbo XS has a crisp, smooth, high pitch sound. This may be due to the location of the outlet of the Blitz BOV in my engine bay too (facing forward). My Turbo XS faces upward.

My question is this....The Blitz makes a fluttering sound at lower boost levels. Through a search I did, I read that the fluttering is actually the sound of compressor surge. If I lower the spring tension on the Blitz BOV will the fluttering (compressor surge) sound go away or is this a normal characteristic of this BOV?

I just want to make sure I don't damage the turbos (obviously).

 

I'm pretty sure it is. My friend had the same blow off valve on his 240sx, depending on the adjustments on the valve, will give you either a flutter sound, or a normal PSHHH... when he opened the blow off valve right up, it would be a big PSHH! But when he closed it ( not completely) it would flutter... my FD flutters...

 

Mine doesn't flutter, and in my opinion it sounds nice with just a deep pshhh. I don't like high pitched BOV. Makes the car sound like a wrx or something like a SRT4

 

ill never decided what bov to get!

 

I like the stock recirculating valve. Yay for stealth!

Anyway, I think it's compressor surge and I think you should do whatever you can to stop it. Not only does it sound like a flock doves under your hood (ghey), but it's bound to toast your turbo(s) eventually.

Honestly, if this is a "normal characteristic" for this BOV, you might consider getting one in which it isn't. I mean, okay, even IF the BOV makes this sound and it's NOT surging, how are you ever going to know, as you continue to tune your car, if you ARE surging? Seems silly to me...

 

With any BOV... if you tighten the spring.. youl get the fluttering sound. If you loosen the spring youl get a "whooooshh" sound.

If you DONT have a BOV... then youl get compressor surge... because the backflow will go towards the compressor wheel once the throttle is closed and the pressure moves the wheel in and out which damages it after a while... and the BOV just vents out that backflow. If you have BOV, 99/100 you wont get compressor surge... unless you tighten the spring so much that it doesnt even open.

 

do you have a pic of how the turboXS one was mounted?

 

You can still see surging with a BOV. It's not like the valve opens a bit and suddenly, like magic, the entire intake side loses pressure. It depends on placement of the valve and the speed at which it opens. It's fractions of a second, but there's still a delay in the discharge. Enough of a delay and you'll get surging. IMHO, fluttering is NEVER a good sign. But that's just me.

The best setup I've seen was a BOV mounted pretty close to the TB, and that mother opened FAST. I knew a guy who mounted his BOV near the turbo (which has also been suggested), but by my fundamental understanding of fluid dynamics, the charge would actually be surging before it was discharged - not ideal. He blew his motor before we found out if the turbo was being damaged, but I stand by the theory. Also, the longer your BOV sounds off, the longer it's taking to discharge. I'm a fan of the low, deep "whoosh" not because it sounds good, but because it's fast and I know the charge is gone. The real high-pitched hissing ones seem like they're taking their time to do the job, and thus hedging towards compressor surge.

Someone once told me that the purpose of the slower bleed on the hissing BOV was to maintain pressure a bit longer. Most people aren't out of the throttle for more than a fraction of a second, especially when dragging or the like, so the increased charge pressure means less time off boost. I understand the concept, but it seems to me that you'd be shifting stupidly fast to "catch" the charge (like < .25 sec) and under most other circumstances, you're just priming yourself for surging.

Eh, to each his own, I guess.

 

http://www.youtube.com/watch?v=MU5Y6d9rh1k

Heres a good video on compressor surge and stuff