One of the members of this forum contacted us at AEM about this issue a few months ago. Our R&D engineers have taken some time to review and address your concerns in detail and created a technical report. We've also created a video using our flowbench to demonstrate the increase in restriction when removing the filter. In that video we also demonstrate the robustness of our S.S. spring reinforced silicone elbow coupler. That's right, our silicone elbow coupler has a S.S. spring imbedded in the material!
But before you read our report or see our video, we need to address the statement quoted above:


Took you guys (AEM) long enough to make it over this way to clear this up and defend yourselves . I'm interested to see the replies to this.

Now if AEM can make a cold air intake system for the HHR SS (it has the same engine as the cobalt ss/tc) that flows better then the stock air box. Can you believe there isn't 1 out on the market yet, hint, hint.

 

"More restriction = More vacuum" is exactly what I was thinking, but is completely depends on where the measurement is taken. The source of the vacuum measurment is what is important here. So, where does the vac input come from?

 

Term was using the pillar vac gauge IIRC, that would be manifold vacuum, not measured in the intake tube.

 

Interesting that they respond as the K&N piece is released-I purchased the AEM elbow last year and would like to know if it's identical to the current offering (with spring). My only (apparent) issue was a stumble just off idle with stock airbox/filter/GMS1-I hope to be able to use the elbow at some point with compatible mods/tuning.

 

Exactly.

 

LOLz.... Term you still running the Hahn anyway?

I have to admit though.... I have seen an AEM coupler flex and suck in... not completely collapse... but you could deff. see it "GET SKINNY" lol.

But anywho... my .02 don't matter in this because I don't have this intake... but as a tuner I would love for all these intake issues to get fixed because they are beginning to become a JINORMOUS pain in my ass

 

I have a new updated AEM intake kit that I need to test. I think I might be able to fully tune out the cold start surge but I not 100% sure yet. I am on the stock airbox for a couple days to test out some new cat heating cam tables before I put the new AEM on the car.

 

LOLz. you are an intake *****... as I have been an intercooler *****.

 

I am sticking with the stock IC for a while.

 

LOL... c'mon man up and get the ETS you'll be glad you did

 

This would still represent a reduction in air flow to your engine, assuming the throttle position was steady (not a factor). Remember, when your turbo is boosting, you will read positive pressure, not vacuum, in the manifold. When the engine is idling, you read vacuum in your manifold. An increase in vacuum beyond that number would mean a further restriction or reduction in flow.

From our OE Performance Parts Engineer:

"I sent a rather lengthy technical report to HB_SS/TC covering the testing we completed to address the various concerns people brought up regarding the Cobalt SS intake. Below, I've written a brief summary of that report:

1. Cold Start Low-Speed Surge or “Fluttering Noise” Summary:
The low-speed surge or “fluttering noise” is a result of our AEM Cold Air Intake providing more flow to the turbo compressor inlet than the turbo can process, all while the engine is attempting to maintain the BPV closed during cold-start. Keeping the BPV closed is probably part of GM’s emissions strategy to increase catalytic converter “light-off” or temperatures more quickly during cold start-up, thereby reducing start-up emissions. As you know, a catalytic converter must be hot to work properly. Note that the BPV solenoid does eventually allow the BPV to relieve the pressure in the compressor stage and the noise goes away once the engine warms up, so there is no danger to your engine. This issue never occurred on a warm engine during our testing.

Also, the S.S. spring inside the AEM silicone coupler does not allow it to collapse below 40in H20 of vacuum as you saw on our flow bench in our development shop. That’s far more vacuum than you will ever see on this engine. Our AEM Cold Air Intake is a bolt-on system designed to provide optimum mid-to-high range street-legal power, so the cold-start issue is a minor consequence. The noise is also more audible with this less restrictive cold air intake than it would be with a more restrictive intake or the stock intake which also functions as an intake silencer. In order to completely get rid of the flutter noise during start-up, you either need to reduce intake flow (use the stock coupler* or other intake with less flow) and reduce power, OR re-adjust the stock PBV solenoid strategy during cold start-up, which AEM does not recommend.

*The engine will not make noise with the stock elbow coupler at ambient temperatures because it is more restrictive and does not flow enough to allow low-speed surge or fluttering. Not enough air can reach the compressor to cause the low-speed surge. (Their coupler was also designed smaller to improve low-end response with this rather large turbo for a stock set-up. See the graph in our report for a comparison on coupler flow.) HOWEVER, we have heard Cobalt SS owner complaints of low-speed surge/fluttering noise with a completely STOCK intake during fairly cold temperature start-ups. Why? The colder air is now more dense, so again you have excess air entering the compressor while the turbo is not spinning fast enough to compress it at start-up, causing the noisy surge condition even with a stock set-up.

For more details on our testing, please see our Technical Summary. I've asked HB_SS/TC to share that PDF report with everyone on this site. Please feel free contact us if you have any further questions."

I hope this helps.

Also from our OE Performance Parts Engineer:

"Using the AEM Cobalt SS Cold Air Intake filter on the K&N Short Ram intake kit:
In this case, we don’t recommend using the large AEM filter provided with our full-size Cold Air Intake kit for use in the smaller K&N short-ram intake for this application. The K&N intake was designed to use their smaller conical air filter, allowing more clearance between their filter and the heat shield. The K&N kit is perfectly good for a short-ram intake, but our filter has a larger cap diameter, so it is nearly cylindrical and does not fit as easily inside their small heat shield. That means the larger AEM filter butts up against the K&N heat shield, reducing flow to one side of the filter. Now, if the assembly can be modified to allow 1 or 2 inches of clearance between the AEM air filter and their heat-shield, then it might flow better. Testing would be required to prove this. However, our filter is best used with the complete, full-length AEM cold air intake system, allowing it grab significantly cooler air down below the engine compartment.

Cooler air = more power.

Please feel free to share all of this information and our report with your friends on the Cobalt SS Forum. Please contact us if you have any further questions or concerns about your AEM Cold Air Intake kit."

That's all for now!

 

I get this low speed "fluttering" on throttle release, low speed driving and I can replicate that noise at will. I did not get the cold start fluttering that a lot of others did and can't comment on that. I'm waiting on the revised AEM to ship out (Joji told me it will be a few weeks as they are in production?) and will run it again to see if the light throttle fluttering still exists. I can tune the fuel trims pretty good and that's no problem at all but the light throttle fluttering worries me.

 

From our report:

As the TurbobyGarrett page states:
"Surge will occur if the bypass valve/outlet plumbing is too small or restrictive (or closed) for the required compressor flow." The low-speed surge noise went away when we installed the stock coupler because of the additional restriction it provided, not allowing a build-up of compressor stage pressure beyond what the turbine stage could overcome at cold start with the bypass closed.

(From “What is surge?” http://www.turbobygarrett.com/turbob...r/faqs.html#t9 )

 

This is directed at KenAEM.
Why is it that your techs(phone techs) are telling people that the intake is only certified for the 2008 model year when the 2009 and 2010 model years are exactly the same? I almost did not get any support from AEM because they told me on the phone that my vehicle is an 09 and since the intake is only for the 08 I did not qualify for tech support. After resolving that issue, I was willing to wait for the revised version that AEM was working on but a few months later was informed that even the revised intake was not certified to work on 09-'10 model years. So I lost confidence in my AEM intake and returned it for a refund.
I understand that it flows more and thus causing a flutter on cold start. Still, its weird that it does not occur with other intakes that also flow more than stock.

 

What is causing my turbo to sound like a sewing machine's whistle?

The "sewing machine whistle" is a distinct cyclic noise cause by unstable compressor operating conditions known as compressor surge. This aerodynamic instability is the most noticeable during a rapid lift of the throttle, following operation at full boost.

This is the symptom that occurs and quite a few if not all others.

 

My guess is they don't want to pay for another CARB EO review or whatever would be neccissary for 09-10. If that indeed is the case its kinda hard to blame them... our cars ended up being such a low run and there are 511 different intakes out for it right now heh.

K&N didn't bother to get CARB approval at all.

 

Well, the point is moot now since the intake is now gone. Still, they should no tbe denying people customer service. I had to exchange strong words on the phone with the tech and he actually told me that I should not have purchased the intake for my car....lol
Anyways, the fact that the intake causes surge or flutter on cold start is not acceptable to me as KenAEM stated earlier. How can putting undo stress on the turbo, BPV and spring several times a day during a cold start, be acceptable?

 

The '08 is a street-legal kit with a CARB EO, and our goal is to offer the same for the '09-'10 model years. It's not that we don't want to offer kits and service for the later model years, legally, we just can't until our CARB approval goes through. Gotta keep things legal. Actually getting CARB approval is another matter altogether, still in process. If we could find a faster way, believe me, we would. We'll keep you posted.


Now more from our Performance Parts Engineer:

"In answer to the following question: 'How can putting undo stress on the turbo, BPV and spring several times a day during a cold start, be acceptable?'

1. Turbo 'stress' (compressor wheel, bearings, and BPV spring)
There is no significant stress on the turbo compressor wheel or bearings or on the BPV spring during a low-speed surge at cold start-up. None. Exactly zero-point-zero. After working at Garrett Turbochargers I can tell you that this temporary, cold-start, low-speed surge condition only makes aerodynamic noise. Furthermore, at these low turbo speeds, the delta-P let off when the ECU allows the BPV to open after warm-up is minimal compared to it's design limit. The BPV can relieve low-pressure through 1,000,000 cycles and not cause any spring wear.

What you may be thinking of is HIGH-SPEED surge.

(See: “What is surge?” http://www.turbobygarrett.com/turbob...r/faqs.html#t9 )

This indeed is a very dangerous HIGH-SPEED situation in which thrust loads may exceed the design load capacity of the bearing assembly. Repeated high-speed surge will cause metal-to-metal contact and wear, possibly causing catastrophic failure of your turbo. Your BPV protects your engine against this, although repeated high-speed surge can wear it down due to the high delta-P it is exposed to. Please see the www.turbobygarrett.com page for more details.

Remember: At start-up, your turbo is running at relatively low speed, so there is no danger to your turbo or engine.

2. "...several times a day..."
In California, we've only been able to replicate this issue no more than twice in one day, and even then only after letting the engine cool down for a full 8 HOURS. We tried for several days. This is because the issues does not occur once the engine is warmed up.

Again, during cold start-up, there isn't enough combined thermal and aerodynamic energy on the turbine wheel to provide enough torque to spin AND compress the now massive volume of cool air that the compressor stage is now trying to process. This causes the low-speed surge, that back-and-forth fluttering whistle you hear at start-up. Fortunately, your turbo is not spinning fast at start-up, (that's why it flutters). However, once the engine warms up and the emissions strategy finally allows the BPV to open, the compressor dissipates pressure and runs normally.

From that point, the warm engine provides plenty of heat and flow energy to the turbine stage, easily providing enough torque to spin and compress all that air in the big compressor wheel.

We tried to repeat the issue as much as possible during testing. This issue should not occur 'several times a day' unless you are living in extremely cold conditions. Engines stay warm for quite some time. Even so, due to the low turbo speed at start-up, there is no danger of damage."

I hope his reply answers your questions
Thanks again!

 

This may be off topic, but will the MAF turbulence issues be addressed in the next revision of the AEM intake?

 

Thank you for your response to my queries. In my case, I work long hours and the car sits for 8-10 hours at a time day after day. So it does go through a cold start at least twice a day like you stated in oyur comment. I know this is just an isolated situation applicable only to me and maybe some other SS/TC owners. I can appreciate that the low speed surge may not be very stressful on the turbo and, again, I thank you for the info you provided. That being said, Im still uncomfortable with the fact that the AEM intake does cause this to happen. I understand that modifying a vehicle from stock is going to change engine dynamics but I myself try to keep the mods from straying from stock as much as possible, all the while gaining the performance I have in mind for my car.

Thanks again for the explenations though. Im sure they supplied answers to questions members on this forum have had for a while