OH MAN, lol, now that there as like 50 Injen short ram intakes sold in a group buy EVERYONE is going to be hearing this for the first time. lmao.
1st, in physics/engineering air is considered a fluid. Everything else EvilMechanic said I agree with though.
Dieseltech, its cool you have experience with poor vacuums on other platforms etc and now you say you fixed it on the Optima, but I do not understand how. You said you simply changed the BOV to an aftermarket and it fixed the problem? If so, then you didn't change the vacuum? and therefore the vacuum wasn't the problem was it? What exactly was done beside bolting on the nameless charge pipe with synapse?
Here's my thoughts & experience. You'll see they fall in line with Evil was saying:
-I have had my BOV in Vent to Atmosphere every since this thread existed over 1 year ago:
http://www.optimaforums.com/forum/6...ussion/2765-diy-vent-bov-atmosphere-pics.html
-I also have the Nameless intake pipe connected to the stock air box. This is how they recommend, the gains are all in better flow through the tube, not filter gains etc.... ANYWAY Key thing here is that 1) still running stock BOV vented to atmosphere, 2) still have the airbox to limit intake noise
-I never heard flutter after doing this, EVER....over 1 year
-UNTIL literally 1 week ago... I hadn't touched the silicone coupler connecting the intake pipe to air box in who knows how long and it had come loose. I immediately knew because the intake had sounded very near stock, BUT now all of a sudden I heard spool and air rush annoyingly loud!...
-Paired with hearing this loud spooling noises, when i'd go hard accels i could now hear the flutter!
-Sure enough, I pop open the hood, see a slight separation/gap between the silicone coupler & air box...It was breathing unfiltered, unrestricted..whoops. I fix the connection, go for a drive and all is back to normal. NO NOISE. all that changed was adding back the airbox's noise & airflow restrictions.
-Also like evil mentioned, no driveablilty or boost etc was any different compared to when I heard the flutter Vs. not hearing the flutter. The performance is the same, the boost levels are the same. The only difference 1 way I could hear it, the other I couldn't. Thats my experience driving on the street, he saw and logged the same on a dyno apparently, per his post.
Now, again this happens in WOT or a "hard" partial throttle, almost WOT... Therefore the BOV is closed or at least should be. If you remove the vaccum to the BOV altogether or use a blocker plate, the flutter noise should still occur. Has anyone actually done this? If so, then that'll put the nail in the BOV-being-the-issue coffin....if it magically goes away, then you know the BOV's vacuum plumbing was the issue all along. That test will point you 1 way or the other, not throwing on another BOV to test, etc....Problem is i'm not making my bpv dysfunctional on purpose for this test, lol (surge?)...AND I think i've proved its not the BOV to myself (and evil to himself) by not hearing the flutter on a vent to atmosphere Valves.
So, to be clear theres an off chance it could be the stock BPV vacuum porting that's creating false vacuum with venturi, BUT you'd hear it with the BPV vented to atmosphere and stock intake left alone. You don't though.
SO whats left? 1) compressor surge or 2) wastegate flutter.. I personally think its ECU controlled flutter with our "high-tech" Electronic Wastegate Actuator...The reason is to avoid #1.
This td04hl-19t can spool pretty **** fast. In lower RPM's a 2.0L engine does not have the airflow capacity to "Accept" past a certain amount of CFM. If a small turbo is spooling so early and creating too much CFM for the engine to handle/pass-though (at that specific RPM) then you get compressor surge. (The other way surge occurs is of course when the throttle plate closes on shifts,etc and air bounces back to the turbo compressor, the reason we have BPV/BOVs)....Theres only 2-3 ways to avoid "too much air" type of surge.
You can improve the Volumetic Efficiency of the engine, basically porting, cams, larger exhaust to minimize turbo backpressures...
Or you can reduce boost/air CFM in the lower engine RPMs...
And/Or you flutter the wastegate on purpose with an electric actuator by command of the ECU, to avoid overshooting the boost in the lower RPMs.
So if you're adding an open filter intake be prepared to hear it unless you a) free up exhaust and/or porting, b) wait til 3k and higher RPM to really gun it, c) get a tune with less boost at lower RPMs, tapering up once beyond 3k rpm....and/or d)go get your 19t compressor housing machined for anti-surge vents
and if you can't/won't do any of that & can't take the flutter noise then go back to the stock airbox, with its air & noise restrictions.