I guess I'll just have TTP look at it when I get it tuned on the 2nd.

 

Unless you have your DV on backwards, it is NOT compressor surge. It is flutter dump from your DV.

 

I just checked, it's on the right way. So flutter dump is fine huh?

 

It's no real big deal. I find it annoying, but oh well. I can't check it out for you since I am still at work (nights) but check out streetfire.net. When you get there do a video search for synapse engineering and check out there videos. One of them is a flutter dump demonstration on a subie with a bov so it is more audible than a DV. Good luck brudda!

 

So what doy uo do if it is compressor surge anyways?

 

If it is compressor surge it is because there is something inhibiting the pressurized air from escaping between the throttle body and compressor and this air attempts to spin the compressor in the opposite direction. This can be a faulty DV, improper installation, or vacuum leak to the DV.

 

So a restriction in the UICP or LICP maybe as well? Hummm.

 

Yeah, the throttle plate!

When I had my stock turbo on the car I could go to 5 psi of boost then let off partially and create the flutter noise at 2500 rpms. Now with the GT30 turbo the same 5 psi is quite a bit more air and the engine just isn't able to consume it all so it stalls and starts backing up into the compressor blades as high as 3500. Getting 5 psi and letting off completely works fine and the BOV/DV discharges the excess boost.

The BOV or DV depending on what you want to call it on our cars should discharge excess pressure but unless you completely let off the throttle it can have a hard time getting rid of the extra few psi left in the piping that your engine isn't using. It's somewhat artificial compressor surge and likely your BOV fluttering.

At WOT it is much more dangerous and for now I'm avoiding full throttle at low rpm's in 5th. I may be able to richen up the tune to reduce spoolup a bit and I'm not sure how Mivec can counter it. Advancing the intake cam and retarding the exhaust cam enhances spool which you would think would make it worse, but it also increases overlap which will let the engine flow more at that lower RPM even if it doesn't make as much power that way. At least that is the way I've read it to work, now just a matter of testing the theories.

 

I must correct myself FLUTTER DUMP IS A FORM OF COMPRESSOR SURGE.

Here's a couple links which do a great job demonstrating what's going on with your DV:

This is what compressor surge sounds like:

http://videos.streetfire.net/video/T...sor_163406.htm

It wont be as loud on our smaller turbos, but it is still pretty noticeable...

Here's a vid on the flutter dump:

http://videos.streetfire.net/video/W...ump_151792.htm

This one shows the delay of the BOV, causing a surging.

http://videos.streetfire.net/video/S...BOV_105407.htm


And for those of you interested since you have X's:

http://videos.streetfire.net/video/E...low_163389.htm

And no I am not affiliated with synapse in any way, nor do I own one of their products....yet lol.

 

Great links! Thanks for the info!

So the BOV you show in that last video is just quicker at opening so it can keep flutterdump to a minimum huh?

What about normal compressor surge? Is there a way to fix that other than getting a better flowing head perhaps?

 

No man you don't want that at all. compressor surge is the worst, thens when you start blowing **** up.

 

Yes...completely let off the gas pedal.

The surge you're experiencing is very mild, normal, and repeatable every time. Like I said in an earlier post, when you're at part throttle and you let off the gas pedal to a lesser part throttle, there's not enough vacuum in the intake manifold to open the BOV. When the BOV doesn't open and the throttle plate is blocking the airflow from the turbo, you get compressor surge. Part throttle surge with little/no load on the engine happens on almost every turbo car and is not something to worry about.

What you don't want at all is surge at WOT or to not have the BOV open at all.