Ok, so I wanted to get to the bottom of the CAI/Short Pipe Intake/Factory Box debate on intake air temps. In short, I wanted to know if I would be sucking in hot air with the Injen Intake set up since it pulls air in around the eng compartment and is not a true CAI. While I appreciate it alleviates some flow restriction, I did not want to offset that improvement by sucking in air if the air was significantly hotter than through the OEM snorkel or some other CAI method. While I don’t know what gains are to be had by the reduction of flow restrictions offered by the Injen set-up, I struggle to believe it is on the order of 15HP. Dyno readings on turbo/IC engines will be all over the map depending on whether the hood was open, heat soak was in play, what carpet blower they used to cool the IC and radiator, etc. Until formal charts are released with the conditions noted, we can only speculate.
Also in question is how much the IC will pull heat out. The amount of heat any given IC removes is a function of its soaked temp, the delta T between itself and the air flowing over it, and the flow speed. The hotter the air blowing through it is, in comparison to the outside air, the faster is can remove it. What is for certain is that an IC can only remove a portion of the heat coming in, and if you put hotter air in it hotter air will come out. An IC will not output air at a constant temp while you vary the input temp. In short, hotter air in means hotter air out, though it’s not a one to one relationship. Thus, you want the coldest air coming in your air filter.
This study does not track air temp coming out of the IC, although it could be measured directly or with a Torque app. The reason I didn’t, or haven’t yet, is because the intake air temp does not react quickly due to the IC’s thermal capacitance and heat soak effects. It is much harder to compare effects of changes by tracking the air temp coming out of the IC unless you control lots of conditions such as idle time, time driving at X speed, the IC’s steady state temp, etc. In fact, I have seen the intake temp coming out of the IC take several minutes to cool down driving at 50 mph+ after idling only minute. For this reason, and knowing the hotter air coming in leads to hotter air coming out, I chose this first study to focus on air coming in.
The set up for baseline measurements is shown here, where I have a TC in the snorkel intake, one outside the air box (motor compartment ambient air), one inside the air box behind the air filter, and another outside the passenger window to take ambient temps. Data was logged with a 4 channel data acquisition unit sampling at 10 Hz.
In the second test, I removed the snorkel to simulate what the air being pulled in the filter would be if it were the Injen set-up. The TC used in the first test to measure the snorkel temp was now used as a second measurement of eng compartment temp. Here’s the two results graphed. The results are alarming to me.
In summary, snorkel does a great job of keeping the intake temps low. The average temp increase was 6 degrees for 25 minutes of mixed driving. Had I not idled so long in the beginning, it more realistically would be about 4 degrees.
The open box test did not fare so well. The average air temp rose to 26 degrees, about 20-22 degrees higher than without the snorkel. If you sat at idle (as in before a race as a red light, for example), the intake air you get to start the race off with is 45 degrees higher than outside! It takes a minute of average driving to bring it down to pre-idle temps. You better believe you IC is soaked with heat now after pumping in air at idle that’s 45 degrees hotter than with a snorkel! If you drove on a the highway, flushing out all the engine heat with cooler air still leaves you sucking in air that is at best 10 degrees hotter and it takes about 5 minutes of this to get to this point. Even more interesting is that the intake air temp in the air box shoots UP at WOT. So the heat your IC is taking out of the charged air is ejected right back in to the air intake box. So the effect of flushing out the eng compartment with cool air is negated by the recirculation of heat back into the air box.
If we use the standard estimate for HP change due to air temp change, Delta HP = HP *1(-sqrt(T1/T2)), where T1 is the original temp in Rankin, and T2 is the new temp in Rankin), then not considering the IC effects we are losing an average HP of 7 horsepower sucking in the hot air. This is average, not peak. We can speculate how much of the extra heat the IC would take out but two things are certain. One, it won’t take it all out and hardly any of it until you reach some kind of speed, and Two: Your IC will be soaked so hot during idle you’ll never recover from the lost power until to drive at speed for a while.
I am sure many out there will reject this study, but I’d like to see someone refute it. My conclusion is a true CAI is in order for out turbo charged / IC engines, and in the real world the Injen intake or others like it do not likely offset the loss of power due to air temps with their improved flow characteristics. So I cannot recommend it, especially for several hundreds of dollars.
Thanks, hope you enjoyed my Sat afternoon project!