This Audi engine sucks air trough a preheater. The preheater stops the intake air temperature getting to cold (in case you didnīt know that). The preheater contains a door, switching between a air pipe inside the grill, and another air pipe whitch takes the hot air around the exaust pipes.

The experiments:

First test I made with the grill air pipes. instead of let them point perpendicular to the driving direction, I had them pointing forward. Almost Nothing happened, ofcourse.

I threw away the silly small air pipes and the small preheater. Instead I mounted a 4" plastic drain pipe that made a perfect fit on the air filter box. That made a nice difference when accelerating from 0. I mounted a aerodynamic inlet (a bass reflex pipe) on the drain pipe, and that made a greater difference. Problaby less turbulence around the edges and more effective suction then.

I was satisfied one week... I removed the whole lid from the air filter box.( The car wanted to breathe! ) And that made more strength at low speeds.

It was clearly that the engine was runing with less power after a while when it got warm as it sucked the air from around the engine. ( Hot air got lower density than cold air and therefore give less power ). Gotta fix it! Want more power! The mad solution I did then was to build a great funnel that took 80% of the grill air directly to the air box...

At that time I didnīt know much about engines. It run great upp to 35km/h but beyond that it felt like a powerless 1 litre engine! The reason was that the engine got to much air and the uppcoming pressure caused the air meter to give less fuel than normal.

So I removed the big funnel with curses and a little violence.

After a while I understood that the fuel mixture system could not work with air pressure. I got an idea how to get loads of air without creating pressure - With a large hole down thru the hood - loads of air with almost no pressure.

It cost me 40 Euro to build it but I believe it gave me around 3 HP more (168HP totally then).