(Hope nobody has done this yet.)
I got some temperature probes (with remote readout) and located them in various places under the hood. There's been so much talk here lately about performance decreases due to the engine breathing hot air. Also talk about how CAI is beneficial and a new hood with scoops, etc. All these cost hundreds of $. So just for the heck of it, I thought I'd see what was really happening. Below is my 1st session and I'll report others (at different ambient temps) if anybody cares.
All temp probes were calibrated with a mercury laboratory thermometer and was found to be within 0.5*C. from 20*C - 60*C. [For the Metrically challenged: *F=(*C x 1.8) + 32] [mph=kph / 1.6] All numbers in *C and kph.

Probe A - between sheet metal in front of left door near rocker panel (for ambient temp.)
Probe B - engine compartment just above and in front of throttle body.
Probe C - inside airbox just on top of JR filter.
Probe D - inside intake tube about 2-3" in front of throttle body.

Session 1: (NOTE: car had a bug screen in front of radiator - see 19 posts further down.)
Run #1
Ambient temp. - 18.0
Wind sp. - 10, gusting to 15.
1st drive of the day, went to store, got back 45 min. later.
1. Upon reaching 3 bars on gauge: B=22.0; C=15.5; D=17.3
2. After 4 min. stop in store: B=49.0; C=22.9; D=30.2
3. Drove for 8 min. after stop: B=41.0; C=20.2; D=28.3
(the above was city driving, stop & go, highest speed:80 kph)
4. Drove out onto highway a short time (up to 120 kph for 15 min.): B=40.0; C=20.1; D=29.1
5. After sitting in garage for 30 min. (shut down): B=70.0; C=52.0; D=66.0 (these readings never got any higher with time)

I'm leaving the probes on the car till I can get some numbers on a hot day. We can get temps here close to 30*C.
So what's this all mean? ELEPHINO (cross between an elephant and a rhinoceros). I've some theories of my own but heck, I got the numbers, you guys figure it out.

 

Wow, nice job! I've been very curious about this myself but never thought to measure it.

I'm very surprised to see the temps shoot wayyy up after 30 minutes of letting the car sit... this might explain why the car can feel like a slug right after starting up the car on a hot day doing stop-n-go errands.

I'd like to see more of these numbers, and also have someone do the same thing with their CAI setup (Greg et al?).

Can anyone explain the exact relationship between higher intake temps to decreased performance? For example if a CAI improves on average of 2 degrees C, exactly how much does that affect performance?

Thanks again, cool post.

 

Thanks, good research.. the data should eventually increase our understanding.

A rule of thumb that many use is that a drop of 10F is worth a 1% gain in power.

 

Did you take the readings while moving? What would be more beneficial is to take the readings while moving.

A. Redline 1st
B. Redline 2nd
.....

and also at a stand still.

Rev engine to 8k or 9k and leave for:

A. 30 Seconds
B. 1 Minute
C. 2 Minutes

You will probably notice that the faster you are moving and the higher engine revs, the closer the temp to the outside air.

 

xviper,

Thanks for posting the data. Definitely keep a log of this so you can plot data later. Might be good to move this to under the hood as well.

Anyways, what I found interesting was the dramatic difference (9 C on the highway) between airbox temperature and temperature in front of the throttle body. It seems a bit unusual that the air would pick up that much heat in 12-15" of travel through a rubber tube, which is a pretty good insulator. Even more curious was that the intake tube temp was lower during your short stop and go driving session at low speeds. This says to me that heat soak in the intake tube might be a problem, but you'd think that with cool air passing through it, the tube would cool off a bit.

I am also surprised that your airbox temps were within 2 C of ambient in both highway and low speed driving. Given the heat picked up from the filter to TB, that seems like an unusually small gain. Did you resample ambient during each test period? I wonder if sampling ambient where you did might play a role. 18 C (65 F) isn't an unusual temp, so I don't know.

Anyways, keep collecting data, this is all useful.

UL

 

[QUOTE]Originally posted by gabedude
[B]Did you take the readings while moving?

 

So how fast do the probes change reading? What I mean is, say the air temp rises 20 degrees, do the probes take 30 seconds to register that 20 degrees or are they nearly instantanious?

 

Not to be an ass here, but I just question things sometimes.

Where exactly are the sensors located? To get an accurate reading of intake air temp, you would have to position the sensor directly in the middle of the intake (not attached to the walls of the tube essentially). Although this is impossible, a bar the radius of the tube with the sensor on the end would give the best results. If the sensor is attached to the inside of the tube all you are measuring is the temp of the tube and not the air.

 

[QUOTE]Originally posted by gabedude
[B]So how fast do the probes change reading?

 

[QUOTE]Originally posted by gabedude
[B]Not to be an ass here, but I just question things sometimes.