Sort of negates the crash bar theory if 50% is removed? Despite the intercooler having a hidden portion it is still effective, don't think of the intercooler as a radiator (which needs all its surface area in air flow) but think of it as a heat sink. It seems straightforward enough. An intercooler acts as an air/air radiator for the intake air, cooling it after the compression of the turbo has caused it to get hot. The compressed air passes through the intercooler, losing its heat to the alloy fins and tubes that form the intercooler core. This heat is immediately dissipated to the outside air that's being forced through it by the forward movement of the car. (We'll get to water/air systems in a moment.) The trouble with this analysis is that - for a road car - it is not entirely correct. The reason for this build-up is that what follows is likely to be seen as incorrect by many people. For example, someone who measures intake air temps while running a turbo intercooled car for a power pull on a dyno, or who drives it around the block, or who sits back and simply theorises, is almost certain to think that what follows is wrong. But, it isn't. In road cars, intercoolers act far more often as heat sinks rather than as radiators. Instead of thinking of an intercooler as being like the engine coolant radiator at the front of the car, it's far better to think of it as being like a heatsink inside a big sound system power amplifier. If an electric fan cools the amplifier heatsink, you're even closer to the mark. In a sound system amp, the output power spikes are always much higher than the average power - for example, big output spikes are caused by the beat of a bass drum. Each time there's an output power spike, extra heat is generated by the output transistors and dumped into the heatsink. But because the heatsink has a large thermal mass (it can absorb lots of heat with only a slight temperature rise) the actual working temperature of the transistors doesn't increase much. And because the fan's hard at work blowing air over the heatsink, this inputted heat is then gradually transferred to the atmosphere, stopping the heatsink temp from continuously rising. Importantly, because the power spike is just that (a spike, not a continuous high output signal), the heat that's just been dumped into the heatsink is dissipated to the air over a relatively long period. This means that the heatsink does not have to get rid of the heat at the same rate at which it is being absorbed. Now, take the case of a turbo road car. Most of the time in a turbo road car there's no boost occurring. In fact, even when you're driving hard - say through the hills on a big fang - by the time you take into account braking times, gear-change times, trailing throttle and so on, the 'on-full-boost' time is still likely to be less than fifty percent. In normal highway or urban driving, the 'on-full-boost' time is likely to be something less than 5 per cent! So the intercooler temperature (note: not the intake air temp, but the temp of the intercooler itself) is fairly close to ambient most of the time. You put your boot into it for a typical quick spurt, and the temperature of the air coming out of the turbo compressor rockets from (say) 40 degrees C to 100 degrees C. However, after it's passed through the intercooler, this air temp has dropped to (say) 55 degrees. Where's all the heat gone? Traditionalists would say that it's been transferred to the atmosphere through the intercooler (and some of it will have done just that) but for the most part, it's been put into the heatsink that's the intercooler. The temperature of the alloy fins and tubes and end tanks will have risen a bit, because the heat's been stored in it. Just like in the amplifier heat sink. Then, over the next minute or so of no boost, that heat will be transferred from the intercooler heatsink to both the outside air - and also to the intake air going into the engine. (end quote) As long as you reduce the intake tract to as short as possible (to minimise pressure drop) you cannot have too big an intercooler.