Is Intake Noise Related to Air Temperature?

[goldstar]

Here's a trivial, fundamentally inconsequential topic that nevertheless aroused my curiosity. Some of you are aware that my modified OEM air intake system uncovers my air intake and opens it up to receive ram air induced by the forward motion of the vehicle. Consequently, my air intake is somewhat louder and more pronounced than the stock version but nowhere near as noisy and obtrusive as an AEM SRI or even a CAI.

However, I and others who ride with me, have noticed that the colder the ambient air intake temperature becomes, the louder and more pronounced the intake noise. In fact, there's a kind of linear relationship between temperature and intake noise with temperatures in the 20s and teens Fahrenheit, cold for my part of the world, yielding much louder sound than say temps in the 40s or 50s. While driving in the Spring and Summer, particularly with temperature in the 80s and 90s, intake noise is considerably lessened. Performance also benefits from a drop in air intake temperature, but thats another topic.

The only explanation I have for this phenomenon is that intake noise is related to air density. As ambient air temperatures decrease, the density of air, and consequently its weight, increases proportionately. This greater weight of air passing through the fixed volume intake duct must be responsible for the increase in sound since this is the major variable here that changes with air temperature. At least, this is my best guess since I can't think of another reasonable explanation.

What do you think? Has anyone else experienced this effect?

Happy Motoring!

[tehstocker99]

The only explanation I have for this phenomenon is that intake noise is related to air density. As ambient air temperatures decrease, the density of air, and consequently its weight, increases proportionately. This greater weight of air passing through the fixed volume intake duct must be responsible for the increase in sound since this is the major variable here that changes with air temperature.

yeah that'd be my guess.


does the intake make a long pssssss noise once you shut off the engine??

[ScOrTGtC]

i dont have that but it has the nice PShh when i shift ...heheheh im a dork J/k... but some honda has that little psss sound when they shut it off... friends tercel had it too.. but the escort didnt have it as much..N/a i meant

[goldstar]

yeah that'd be my guess.


does the intake make a long pssssss noise once you shut off the engine??

No. Although my mod causes louder than stock intake noise, shutting off the engine causes an immediate end to the sound. When I ran my AEM SRI however, I did get that pssssss noise you refer to after shutdown.

Happy Motoring!

[elscotto80]

I hit migher boost levels when it is colder out. I am assuming that is related to this also perhaps??

[ScOrTGtC]

thats true too.. when its cold my car hits 11 psi when warm outside it hitsonly around 9 and its soooo slugish...

[1st Gen]

I read somewhere a long time ago that the internal combustion engine actually runs on air. (I always thought it ran on gas myself) It’s the expansion of air that causes the engine to function. With that, cold air being denser than hot air resulting in more material for expansion, the end result being more excitement during the combustion process. More noise.

As for the hssing, I was in the auto parts store the other day and they had a display comparing air filters. The paper oem filter didn’t allow nearly as much air flow as the aftermarket intake that it was compared to. With that demonstrations, I can deduce that the paper filter causes a low pressure system inside the cold air intake that only equalizes once the engine has stopped running. The after market filter offers little resistance to the air flow and thus will equalize almost immediately after shut down. No hiss.

I have noticed that my car has more HP at lower elevations. Again, denser air.

[goldstar]

I hit migher boost levels when it is colder out. I am assuming that is related to this also perhaps??

Yes. In a turbo engine, the density of the air charge is always less than the pressure ratio due to heating caused by compression. Considering only the change in ambient temperature, as ambient air temperature decreases and density increases, the density ratio will more closely approach the pressure ratio resulting in increased boost levels, because the cooler the air going into the turbo inlet, the cooler and more dense the air leaving the intercooler and entering the cylinders.

Reference: Maximum Boost, by Corky Bell; Chapter 3, page 27

Happy Motoring!

[1st Gen]

Yes. In a turbo engine, the density of the air charge is always less than the pressure ratio due to heating caused by compression. Considering only the change in ambient temperature, as ambient air temperature decreases and density increases, the density ratio will more closely approach the pressure ratio resulting in increased boost levels, because the cooler the air going into the turbo inlet, the cooler and more dense the air leaving the intercooler and entering the cylinders.

Reference: Maximum Boost, by Corky Bell; Chapter 3, page 27

Happy Motoring!

I'm going to buy that book right now

[goldstar]

I read somewhere a long time ago that the internal combustion engine actually runs on air. As for the hssing, I was in the auto parts store the other day and they had a display comparing air filters. The paper oem filter didn’t allow nearly as much air flow as the aftermarket intake that it was compared to. With that demonstrations, I can deduce that the paper filter causes a low pressure system inside the cold air intake that only equalizes once the engine has stopped running. The after market filter offers little resistance to the air flow and thus will equalize almost immediately after shut down. No hiss.

I have noticed that my car has more HP at lower elevations. Again, denser air.

It's quite true that oiled-cotton fiber air filter elements such as the K&N type flow more air than equivalent size paper elements. However, given sufficient area, paper elements are more than adequate in given situations where oiled-cotton elements would be overkill and could cause problems from the deposition of oil on the MAF sensor. You might want to look at:

https://www.wihandyman.com/forum/showthread.php?t=2370

It's also true as you say that your car has more HP at lower elevations because of air density considerations. If interested, for more info relating air density and elevation to HP output, check out:

https://www.wihandyman.com/forum/showthread.php?t=1361

And yes, the Corky Bell book is extremely interesting and informative. Highly recommended.

Happy Motoring!