I do UL (Underwriter's Laboratories) experiments every once in a while at work. And so I had the brilliant idea to bring some of the test equipment into my car. Specifically, the thermal couples that are used to measure temperature at specific points. There's a hot (excuse the pun) debate on whether the Injen CAI, Placeracing CAI, and popchargers really take in different temperatures of air in the engine bay. So I decided to wire up some thermal couples and drive around. The results are quite interesting...

Probe #1
I placed one right behind the driver's side foglight bay (I don't have any foglights, so it's straight ram air). This would be pretty close to where the place racing CAI would be, except in the wheel well and not directly exposed.

Probe #2
I had another thermalcouple taped to the filter of my Injen CAI, this intake sits right behind the radiator (not the best place, but the only place if you don't want to cut holes)

Probe #3
And one more was placed where your favorite WAI would normally go.

Probe #4
As a control, I had one located outside of the engine bay for ambient temperatures. It's was cloudy/scattered showers in Dallas, Texas at about 65F.


Fired up the engine and went for a little drive. I drove three different stlyes: Normal start/stop traffic, aggressive WOT, and cruising on the highway. Turning A/C off or on made no difference at all. Results?

Probe #1 kept at a VERY steady 65 degrees, I figured it would be actually colder with all that wind. But I guess that's windchill not temperature.

Probe #2 Was the HOTTEST out of all the the sensors. Sitting behind the radiator the probe would read anywhere from 90 degrees up to 130 degrees. At idle, or at a stop light, it would increase a slight 5 degrees and settle because the radiator fan would kick in.

Probe #3 the big surprise... This probe had the most fluctuations. At idle or at a stop light it would heat up to the same temp as the probe #2 (the CAI). Sometimes it would be hotter, but most of the time it was the same temp. But the interesting thing is that when I was driving and cruising, the temperature would drop to about 10 degrees above ambient (so mid 70s) so actually it would be about 20-30 degrees COOLER than the COLD AIR INTAKE.

This kind of data made some interesting conclusions. And I guess you can draw your own or discuss on this thread... I think from a standstill, the Cold Air might have a slight advantage since the engine bay heats up. But from a cruising speed, it sure does look like the WAI has the cooler air flowing into the engine. The best would place for the intake would probably right at the fog light, where there's plenty of cold air flowing there, however it's more susceptible to water entering.

What do you guys think?

Makes me feel better about my ghetto WAI!

+1 to that FNG, bomz piping and a big ol k&n = 55 bucks shipped. compare it to 200+ for name brand cai? yikes

Haha...Finally everyone will see how much $$ is wasted on getting an Injen.

Good work.

I've got two thermocouples installed, one in the CAI just before the SC blower inlet, and the other just before the throttle body.

I usually get about 10-15 degrees above ambient at the blower inlet (I think the thermocouple may be seeing a little radiant heat energy from the blower) and about 30-35 degrees above ambient at the TB. A week or so ago I removed the passenger side fog light so that the air filter gets a more direct flow of air. It made no difference at all in temperatures. So the foglight is back in.

Did you have the thermal couples inside the tubing or taped/epoxied on the tube

now that is interesting and good work...I do have a question however, is the proper setup to have the filter for the CAI in the fender liner right? which actually does not have direct air flow...I wonder what the results would be from that, and if the excess heat from say hot pavement or brakes would impact those numbers? Also what kind of unit are you connecting the Thermocouples to? (ie multimeter? (what kind))

Thanks and good work!

They are inside the intake pipes. I have the Autometer dual channel intake air temp gauge that comes with two thermocouples on the end of probes. I drilled small holes in the rubber 3.5" hose I am using to connect the CAI pipe to the blower inlet and the IACV bypass hose. The probes are a tight fit in the hole so there is an effective seal against air leakage.

Here's the one at the IACV hose. The end of the probe is about in the middle of the intake air stream.

The thermal couples are connected to switch box which is connected to a Fluke thermalcoupler multimeter measuring device.

I was planning to stick a thermal couple down where the place racing CAI goes (in front of the wheel and inside the front quarter panel), but I never got a chance, maybe next time I snag the thermal couple machine.

based on the data from behind the foglight hole (with no fog light, so the probe is directly being blown on) it's very close to ambient. Even when there's 70 mph winds blowing into that hole it won't get cooler than the ambient at the time 65 degrees.

My understanding (not much) is that with an intake the key is to get as much cold air at as fast as possible speed into the intake manifold. The CAI is better probably not because of temperature, but mainly because it's able to have the ram air effect being near the front of the car.

Wouldn't you just need to know the temp of the air right before it get inside the TB for the best comparison?

No, the CAI is for temperature, at least the ones in the fender well. To take advantage of ram air, the intake pipe has to be positioned at the stagnation point of the air flow hitting the vehicle. Even with the fog light removed, a fender-well mounted CAI is not going to get much ram effect because it is too far removed from the stagnation point. Maybe the setups where the intake begins at a removed headlight, which is about the height of the stagnation point on a Maxima.

Would the CAI being in the fender well be in a somewhat vacuum state? Being sealed (of course, not air tight) it would be harder for air to flow. As opposed to the CAI behind the radiator is more in the open and can draw air more easily.


I guess the only way to really know is to dyno the different intakes on the same car.

There are plenty of pathways for air to enter the fender well. I went ahead and cut a 3" diameter hole in the bottom of the liner, anyway, just to be sure.

Excellent thread. And this afternoon it turned into just what I need to know.

Imobejoas, or anyone - anybody have access to a pressure switch to measure air velocities around the frontal area of the 4th gen for a ram intake?

On the Taurus for instance the very best place for the intake isn't right at the center middle bumper, but below down by the airdam.
http://www.v8sho.com/SHO/LocationofColdAirIntake.htm

What's the flow like on our cars? - bumper vs license plate vs airdam vs foglight opening vs headlight opening, etc. I'm not convinced the stock OEM location right below the hood is ideal.

I've been researching much of this using Autospeed of Australia (requires subscrip). For instance...
http://www.autospeed.com/A_1361/cms/article.html
http://www.autospeed.com.au/cms/A_2081/article.html

I've pretty much got a solution to a colder than ambiant intake but need a ram air to feed it.