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CAI Question

2K views 31 replies 12 participants last post by  patty AT forge 
#1 ·
I recently installed a CAI this weekend, and I didn't realize the boost pressure would dump and kinda flutter through the air filter as well after releasing boost under hard acceleration. This is correct, right?
 
#2 ·
I dont know what CAI stands for, please enlighten me.
But i do know that this does not sound right. You should not hear dumping during acceleration.
You might hear the whistling sound of the turbo spoolup, but this is just for a second, from approx. 2000-2500rpm, pedal to the metal. Depending on your sw.
 
#4 ·
CAI - Cold Air Intake

The problem isn't "during" acceleration, it's when releasing boost. My atmospheric BOV releases pressure, as well as the CAI. I'm pretty sure this is common, but wanted a clarification. And, when releasing pressure under heavy boost, the rush of air will make the CAI flutter.
 
#6 · (Edited)
That's exactly what I thought the problem was - compressor surge. I just installed a Forge BOV on my car last week and ordered the tuning kit as well. Well, the tuning kit was backordered, and the BOV comes with the yellow spring installed.

I guess I better call and find out if they've got the tuning kits in stock again.

Is the popular opinion here that I'm experiencing compressor surge through my cold air intake?
 
#7 ·
It shouldn't be anything to do with the CAI - chances are you're just hearing it more because of the lack of airbox, plus it might have raised your boost level a little...
 
#9 ·
Sounds to me(but I'm no expert, so take it with a grain of salt) like the Forge valve is where the noise is coming from, but you're just now hearing it clearly because of the lack of airbox.
 
#10 ·
Alright...so, please correct me if I'm wrong.

When you hit the gas you make boost. When you let off the gas, the throttlebody plate closes and the air compressed inside the pipes has to go somewhere - to your bypass valve or blow-off valve. If you didn't have a BPV or BOV, the air would have to exit, and it would would take the path it came from - back through the turbo. The air would travel backwards through the blades in your turbo resulting in turbo flutter and damage over time.

So, it would seem to me that the spring in my BOV is too stiff, thus, not allowing the proper amount of air to escape and forcing some of the air to travel backwards through the turbo causing a fluttering sound which is amplified by the CAI the air is exiting from after passing through the turbo.
 
#13 ·
normal

saab_1999 said:
I recently installed a CAI this weekend, and I didn't realize the boost pressure would dump and kinda flutter through the air filter as well after releasing boost under hard acceleration. This is correct, right?
My old 900 used to do this 'fitititititit .......... ' air filtering through the air filter after dump , sounds cool , my present 900 doesnt do it . the first DV was a Bailey and the present DV is a forge ( not as good i dont think , the bailey has a stronger spring and is made nicer )

other than that its perfectly normal , check out that fast furious 2 film at the begining in his nissan , you can hear the turbos ' fitititititit- ing away through the air intakes ..... although thats not cool cos its a .... nissan :confused:
 
#14 ·
TurboTempo said:
My old 900 used to do this 'fitititititit .......... ' air filtering through the air filter after dump , sounds cool , my present 900 doesnt do it . the first DV was a Bailey and the present DV is a forge ( not as good i dont think , the bailey has a stronger spring and is made nicer )

other than that its perfectly normal , check out that fast furious 2 film at the begining in his nissan , you can hear the turbos ' fitititititit- ing away through the air intakes ..... although thats not cool cos its a .... nissan :confused:
The noise that you describe would be compressor surge and its presence with the Bailey valve disproves your sentiment that it is a better valve ;)

Also our valves can be configured via different springs to handle between 3-40 psi...
 
#15 ·
saab_1999 said:
I recently installed a CAI this weekend, and I didn't realize the boost pressure would dump and kinda flutter through the air filter as well after releasing boost under hard acceleration. This is correct, right?
This could be an indication of surge depending on what conditions it occurs under. If the initial sound when lifting after a full boost run is this flutter than it is most likely surge, however if it just flutters towards the end of the vent under the same conditions it is of no concern. If its a partial boost thing it isn't a concern either.
 
#18 ·
Yellow can mean pretty much anything - IIRC it's generally taken that the top of the yellow / just going into the red is around 11psi but as I say, it's very difficult to measure without an aftermarket gauge.

For reference, mid way through yellow on mine (which I think is around the level that base boost is supposed to be) is 8-9psi.
 
#22 ·
when I had my CAI on my car, I would always hear compressor surge. I could be boosting 1psi and light on the gas and I would still hear it. It actually made my car too loud in the cabin. All I would hear is air rushing. It was really annoying. And this is coming from a guy who has a 3in pipe with no muffler on the car.
 
#23 ·
okay

patty AT forge said:
The noise that you describe would be compressor surge and its presence with the Bailey valve disproves your sentiment that it is a better valve ;)

Also our valves can be configured via different springs to handle between 3-40 psi...
ahhh i see , Okay patty thanks. that reminds me actually , the bailey was an atmpospheric dv and the forge is a recirc , so my sentiments paired with my useless memory really doesnt help anything much . maybe the fititititit noise wasnt coming through the air inductor/filter after all but possibly the bailey spring being ..... too soft ?

i dunno blooming interesting though :)
 
#24 ·
That's not compressor-surge.
That's a fluttering BOV.

At nearly-zero boost, there's not enough pressure to hold the BOV's diaphragm tight. when that happens, it'll flutter open/closed. The turbo will be spooling, as if to build boost, but the valve is just dumping the pressure. in DSM's we "crush" the valves (they have metal housings) and it preloads them a little extra. usually eliminates the flutter. I get it all the time. the simple fix is to lift the throttle a little, or mash the gas. The latter makes me a little happier.



Muuuuch different than compressor surge...
 
#25 ·
G96nt said:
That's not compressor-surge.
That's a fluttering BOV.

At nearly-zero boost, there's not enough pressure to hold the BOV's diaphragm tight. when that happens, it'll flutter open/closed. The turbo will be spooling, as if to build boost, but the valve is just dumping the pressure. in DSM's we "crush" the valves (they have metal housings) and it preloads them a little extra. usually eliminates the flutter. I get it all the time. the simple fix is to lift the throttle a little, or mash the gas. The latter makes me a little happier.



Muuuuch different than compressor surge...
Exactly. It would make life much easier for me if everyone that owned a turbo car could go for a full throttle drive in a car with absolutely no means to relieve boost pressure so they can hear the difference... its very hard to diagnose the cause of a sound via the internet :cheesy:
 
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