Mike2kS4

But in the intake tract, the item with the most mass and heat exchange capacity that air passes through is the IC. It *should* easily neutralize such relatively small effects... Look how long it takes on a WOT run for the IAT's to even start climbing in most cars: Theres *lots* of thermal stability there given how rapidly the compressor outlet temps are rising. Yea, this is due to a combination of factors, but still, the IC is *the* major player and significant heatsoak is the only condition that brings out a decrease of IAT's *in boost*.

My RX7 had a VERY short, large diameter (3") plastic intake tract that consistently exhibited this phenomenon. Upon changing the IC (larger, stock mounting position, better duct, only change) it *totally* went away.

Ah10@WMS

i would consider IPP IC just not as effecient as RS4 or AWE ic thats all!

Flyboy

I think you're underestimating the heating that takes places in the intake during low flow rate conditions. Consider that the majority of the path that the air follows is in piping that is right alongside the engine. I've taken some measurements of temperature at the outlet of the Y-pipe and the temperature under steady state driving is 10F higher than ambient, under stop and go driving the temp goes up more. The rest of the piping leading to the turbocharger inlet goes right alongside the exhaust manifold. I don't think it's a stretch to guess that the intake air is 20F warmer by the time it reaches the turbo. That has a substantial impact on the compressor outlet temperature.

The heat soak you refer to happens all along the intake, not just at the IC, and I don't think relative to the IC the other heating is negligible. Under steady driving the air passing through the intake can carry heat off, cooling the intake system, so that the temperature differential between the intake piping and the intake air is less, thus when you mash the pedal and the airflow increases the temperature change isn't as great.

I agree the same thing is happening at the intercooler, but I just think people focus way too much attention on the intercooler as the source of heatsoak. The IC is the one piece of the intake that is specifically designed to lose heat, and it is located in a position to facilitate doing that. But it is simply a heat exchanger and you have to consider the energy balance. If the airflow from vehicle movement is insufficient to carry away the heat that the intake air is supplying, the IC core will heat up. Stop and go driving encourages heating of the intake system, which heats the intake air, and discourages heat removal because of low flow rates of ambient air. When the car speeds up, as on a fats, the reduction in intake air heating, because of the speed at which the air spends in the intake piping, combined with the enhanced heat removal from the IC core resulting from the faster speed, gives a net decrease in temperature, until the volume of hot air passing through the core and heating it exceeds the capacity of the ambient airflow to remove that energy, then you see the steady climb in IAT.

Mike2kS4

I wasn't totally dismissing the intake tract, but I really didn't see it as a major player in such a short-term (couple second) change that requires a fairly significant transfer of energy... BUT, given your compressor inlet data, that makes sense sense now. 10-20F pre-compressor is huge.