I haven't got a Phase kit, so I can't comment.I think the phase kits ignore the knock sensor... aqnd possibly lambda too.. and just run from TPS & air mass meter ?
It would be stupid and dangerous to ignore signals from fellas likes the lambda and the knock sensor. This can easily be proven, actually, on a dyno. Slightly knocking the block with a hammer should activate the knock sensor. The lambda sensor is only involved during closed-loop operation, again easy to check (disconnect it!)
I doubt that the Germans would create such a hack, though...It's not the surface area, it's the internal shape that creates the drop. A long and narrow air passage creates a lot more drop than a bunch of shorter, wider passages.ICs, why would an IC with a good surface area ( lets say 30cms x 60cms cause boost drop ?
It can make the difference between 5psi and 1psi drop.
Example: The stock i/c creates a pressure drop of 3 psi (according to Astra 16v SC in an earlier thread). If you connect three of these intercoolers in series, you'd have 9psi drop.
If you connect them in parallel (one behind the other, like a very thick core) you'd end up with 1 psi drop. The inner one wouldn't do much cooling, but you get the picture.
That's very important, because in the first scenario the turbo would have to work harder to produce 5psi extra for the same manifold pressure. These 5psi (say at 15psi) would raise the charge temp by 30-35C, maybe more (the turbo is working well outside it's efficient range now)
This would result in the cylinders inhaling at least 10C hotter charge, ie 2.5% power loss due to the restrictive i/c design
The extra heat circulating in the engine bay won't help much either...
*Some* pressure drop is inevitable, as the hot charge molecules have to swirl and make friends with the inner core passages, so that they share their heat. (it's a heat exchanger, dammit!)
But *too* much swirling and dancing and back and forthing won't lower the charge temp much more, while obstructing the airflow unacceptably. It's a balancing act.