Intake Air Temp Experiments

[JimR]

I have been thinking of relocating my apexi filter to beneath the passenger headlight, for cooler air. I wanted to test what kind of a difference this would make to air mass, so I did a bit of an experiment.

Keep in mind that this is NOT a controlled environment! Your results will vary. Anyway, I took a thermometer and attached it to my air filter in it's current location (where the airbox used to be), and then moved it to the space under the headlight. Here are my results:

Test1, highway driving at ~140km/hr
Outside temp: 25c
Under headlight: 25c
In engine bay: 35c

Test2, city driving at ~50km/hr to ~70km/hr, stopping at lights, etc
Outside temp: 15c
Under headlight: 19c
In engine bay: 45c

Both of these are actually averages of a couple different tests I did in either situation.

So, I run the numbers:
Test1, (35c + 273c) / (25c + 273c) = 1.033 = 3.3% more air mass will enter my engine for a given flow rate.

Test2, (45c + 273c) / (19c + 273c) = 1.089 = 8.9% more air mass for a given flow rate.

Cool! I can get more air into my engine! Now, the question I have been puzzling over. How will this affect fuel cut?

I am currently hitting fuel cut at around 12psi. From what I understand, the ECU determines fuel cut from a number of things, including the air flow rate (via the karman vortex), plus air temperature, and altitude via the ecu sensor.

If the ECU does take all these factors into account, then I believe this won't make any difference to fuel cut. But I read somewhere that an air meter frequency of 1500hz will trigger fuel cut.... regardless of the other factors. I would love some clarification there.

Feel free to chime in with your opinions/questions/etc.

 

[IJ.]

Sounds about the same as I found earlier this month on the Dyno.

We were seeing 45c at the AirFilter and 82c at the Manifold I fitted a CAI the next morning and had a 20c drop at the Manifold under boost and +3c over ambient cruising.

Boost at the same controller setting jumped 5 psi just with the CAI.

Be careful that it can't ingest water from puddles.

 

[JimR]

I have all the plastic undercovers in place and they are in good condition, so I should be ok for water. It doesn't rain much here either.

If the same thing happens with my stock electronics setup, then I will have to turn down the mbc to avoid fuel cut! Is this right? I won't mind.... slower turbo rpm, longer life, less heat, etc etc. But I'd like to know what to expect.

 

[IJ.]

My "guess" will be you'll have to crank the MBC right back to keep under fuel cut as the charge is so much more dense at the lower temps!

I have all the math here in a turbo book but couldn't be bothered running the numbers when it was easier to just crank the AVC-R back to 22 psi!

I also noticed that after setting the EBC on the dyno to 30 psi out in the real world the CAI was so much more effective I had to pull 3 psi out to get it back to 30!

I just routed a 4" flex hose out through the snorkel hole.

CAI

 

[boost fiend]

ok, im thinking of going this same path(air filter under the bumper)....



but im lost on what a cai is. sounds intersting.

nevermind...... drunken brain fart. duh, cai = cold air intake.

**(yelling at self now)**

 

[johnathan1]

IJ: I'm confused...where is your upper IC hose? Couldn't the CAI be routed to the stock airbox snorkel hole (a.k.a. under the headlight)? Do you have an air filter at all? And what is the little bullhorn thingy? Do you have a PA system, or is that just for an alarm? Haha, sorry...I'm very inquizitive! :biglaugh:

 

[IJ.]

Jonathan: The big black cylinder is the Aircleaner there's a K&N Pod in there.

The Horn is the alarm siren

The IC Pipe is under all that and goes out under the headlight.

 

[GTsupra]

i just put mine straight throught the front where the original air hole.