Hey guys, if this is info that everyone else has figured out, let me know.

We've spent quite a bit of time trying to tune out and research why DV flutter happens. Most think that it is the BOV (whatever brand you may have). We've tried every configuration possible. We tested today without a BOV in the system and it still did it.

Scenario: Part throttle, boost comes in while in part throttle, and boost pressure oscillates.

Since the OEM boost gauge tends to dampen out any major vibrations you never see the phenomenon with the factory boost gauge. So we connected an industrial gauge just to make sure, and voila, the pressure gets very unstable without a BOV in the system. Basically, at a given point the pressure oscillates +- 5 psi. We can only conclude that this is true compressor surge.

This is not a phenomenon that we see with stock turbo cars. Either with cams, or without, we don't see this happening to cars with the stock turbo.

Here's the specs on the test car:

Evo IX
IC piping and FMIC kit
Tuned with GM 3 port solenoid
Heavier sprung WG actuator
Bigger aftermarket turbo

Bottom Line: Your BOV has nothing to do with it!

 

so what is the solution again?

 

Different turbo . . .

Maybe, a wastegate that opens sooner to relieve the backpressure. But I haven't tested that yet.

Basically, this is genuine compressor surge. Not just flutter when you let off the throttle. What we've defined today that can help anyone is the following: If you are seeing boost pressure at the factory boost gauge, AND you're experiencing what you think is DV flutter, then it isn't the BOV. There's no way that the BOV should be open (with Synchronic anyways) if there is boost pressure in the intake manifold.

 

I've found that softening the preload on the adjustable BOV's to a pressure that is less than the engine vacuum at idle is usually sufficient to almost completely eliminate the flutter that most experience as described above. Also setting the boost to high for the efficiency of the compressor wheel will induce surge as described above.

Josh

 

I have this problem and yes, it is compressor surge. You can even graph the boost/load oscillations. The graph below is a mix of 2 runs, so just take a look at the load curve (boost curve is pretty similar, just not graphed here).

Stock Evo VIII turbo, stock cams. Intake/O2/TBE/Evo9 MR Metal DV/3 port WG.
I´ve not gotten around to try to solve it since I´m changing turbo and cams soon. Lowering WGDC values in low rpm´s should help ( but spoolup will suffer).

 

I haven't seen this on Stock EVO VIII turbos, either with cams or without

 

I thought it was pretty well known the EVO IX turbo surges?

 

It has been seen with VIII's. It was thought that cams were the cause, but alas, nope.

 

It occurs when people attempt to force the stock turbo to produce more boost by using stiffer springs in WGA or increasing the preload, or using boost controllers and other mechanical means to increase boost. The part throttle surge is typically induced because the throttle opening at part throttle is not enough to prevent the pulse back into the compressor housing. The turbo spools very quickly in this case and the efficiency of the compressor wheel exceeds the ability of the partially open throttle body to flow at that point. I have experienced this on my stock VIII turbo when running 24 psi by using a EBC and Forge WGA. I was able to almost completely tune it out using the Synapse Synchronic BOV. I will report on my new setup once I am done tuning.

Josh