PDA

View Full Version : The infamous hissing from CAI


Mr Paddle.Shift
12-28-2001, 11:37 AM
So whether it's ECIS or Dinan or Ben & Jerry's CAI, those who have one of the above is faced with the hissing noise. What was the latest update about the hissing? If I not wrong, some believes it is because of the K&N cone "performance" filter.

Here's my version of the explanation. A quick recall to fluid mechanics is a possible occurance of cavitation. Not too technical I hope. Cavitation can be produced when the fluid velocity is increased with a reduction of flow area followed by a decrease in pressure. This pressure decrease can be large enough such that the water molecules (humidity) in the air flow vaporizes. This presure point is otherwise known as the vapor pressure.

With sufficient restriction a hissing sound can happen.

So, where is this restriction along the aftermarket CAI? I would think it might be the aftermarket hose connector prior to the AFM.

A good experiement is to run the car with the CAI in a dry-air environment. If the hissing sound disappears, then the point is proven.

One last point. Does the stock air box produces any hissing sound? Well, if my ears haven't failed on me from the countless visits to rave parties, yes it does produce a very faint hissing sound. Only to be dispersed and resonated within the rather spacious stock airbox.

Thoughts and comments? ;)

alee
12-28-2001, 02:33 PM
I believe ECIS claims the problem comes from the throttle plate (?). I think Sean @ ECIS actually has a list of parts that you can get to reduce/eliminate the hiss.

-Al

The HACK
12-28-2001, 06:08 PM
Originally posted by alee
I believe ECIS claims the problem comes from the throttle plate (?). I think Sean @ ECIS actually has a list of parts that you can get to reduce/eliminate the hiss.

-Al

I wonder if Sean has tested an ECIS equipped car with these parts. If it decreases power and torque I'd rather just live with the hiss. If not I'll get it.

On a slight side note, my wife is now complaining about the hiss. She thought something was rubbing against the front driver's side wheel or tire. So, if Sean can provide some solid test data regarding these parts I would definately be up for getting a set and try to eliminate the hissing sound.

LilEccentricJ
12-28-2001, 06:17 PM
Vince, what temp reading do you get from the AIT at idle? I'm getting like 130F and under moderate throttle it will get down to a temp about 15F above ambient with the OE intake setup.

Mr Paddle.Shift
12-28-2001, 07:57 PM
Well, it all depends on ambient temp. I gathered some data just last week. Idling is about 100F and
lowest about 62.6 F.

Do you have the stock intake?

Originally posted by LilEccentricJ
Vince, what temp reading do you get from the AIT at idle? I'm getting like 130F and under moderate throttle it will get down to a temp about 15F above ambient with the OE intake setup.

LilEccentricJ
12-28-2001, 08:03 PM
Originally posted by VinceTopasBlau3
Well, it all depends on ambient temp. I gathered some data just last week. Idling is about 100F and
lowest about 62.6 F.

Do you have the stock intake?



Yes with the stock intake... I'll have to watch this closely. My thought here is this; if the idle AIT is drastically higher than ambient then the take-off power ability of the car would thus be reduced. As I said, when the RPMs were up the AIT would come much closed to the ambient temp but when you are already in motion, absence of restriction becomes a more important factor than temp. It is at a stop that a CIA would shine then. Thoughts?

Mr Paddle.Shift
12-28-2001, 10:13 PM
Hmm..I presume you meant AIT = IAT (intake air temp) and CIA = CAI (cold air intake) :)

Yes you are right about being stationary and in motion. In addition, when in motion, the pressure of the air intake is quite important too. Check this out:
http://www.autospeed.com/A_1023/P_1/article.html


Also, remember the IAT sensor is located quite near to the engine. I am not quite sure how the air flows around the sensor, but depending on the sensitivity of the sensor, we can obtain quite inconsistent data.



Originally posted by LilEccentricJ


Yes with the stock intake... I'll have to watch this closely. My thought here is this; if the idle AIT is drastically higher than ambient then the take-off power ability of the car would thus be reduced. As I said, when the RPMs were up the AIT would come much closed to the ambient temp but when you are already in motion, absence of restriction becomes a more important factor than temp. It is at a stop that a CIA would shine then. Thoughts?