Intake air temperature plays a huge role in power production. The cooler the air, the more power you can make. There are two potential downsides we saw with the V2 for the Civic Si:

1. It is a "warm air" intake.
2. The intake tube runs over a radiator hose.

There isn't much we can do about the fact that the V2 is a warm air intake, however, the placement of the air filter may draw in cooler air. The filter sits near a gap between the wheel well and the engine bay (see right photo). Since this car will be a track car, this placement may not help much at the track because we can expect heated air (on the order of several hundred degrees F) coming from the front brakes. For the street, this placement may be more suitable.

Shawn and I drove around Torrance in the V2-enhanced Si while logging intake air temperatures. We found that in the stop and go traffic around Torrance, the intake air temperature ranged from 50F-60F above the ambient temperatures. This seems to be a bit high. On the dyno, we saw about a 20F-30F temperature differential, but we had the hood open and a fan blowing toward the engine.

To mitigate the effects of the radiator hose and fan, insulating the tube is necessary. I bought reflective pipe insulation from Home Depot. The insulation has an R factor of 1.6. Near the radiator hose, I double wrapped the intake tube. The plot below shows the intake air temperature (green curve) and the engine coolant temperature (blue curve). I used my laptop with an OBDII package to log the temperatures as I drove around town. The ambient temperature was 62F and the intake air temperature stabilized at 79F if I kept the car moving. When I stopped on my driveway for a few minutes, the radiator fans kicked in and the intake air temperature rose to 102F, 40F above ambient. We will revisit the temperature testing in the summer when the ambient temperatures are higher.

So, what does this data tell us? If you are sitting at a stop light or driving slowly (i.e. the intake air speed is low) and the radiator fan kicks in, the intake air temperature will increase significantly. As long as the car is moving with enough speed to keep cooler air coming into the engine bay, the air intake temperatures are cooler. We agree with AEM that though the intake tube may be warmer than the ambient air under the hood, if the air inside the intake tube is cool and moving fast enough, the intake tube does not have time to heat up the air. Since we will be tuning this car for track performance, the under hood air temperature is not a primary concern for us.