Note: Upgrade performed on a 1997 Audi A6 2.8L

Let me share with you a really cheap way to make your car response better, especially after hours of driving, and in hot wheather like what I have here in Malaysia all year round.

The basic principle is, cooler air intake improve engine power output. But what many do not know is, your engine must know about it in the first place.

What triggered me was, when I drive the car long enough, high speed, hot day, the car power felt like not as good as in the initial part of the journey. Kick down was also somehow retarded. After I stopped for a while for meal break, the car power seems to come back.

The Audi A6 that I have is using an air mass sensor to measure the amount of air mass intake, and adjust fuel mixture accordingly. Upon examining of the air mass sensor (right after air filter housing), I can see some thin wires running across the cross section of the opening. From here, I guess that Audi is using "hot wire" method to measure air mass: when the relatively cooler air flow pass the electrically heated wires, the amount of air passing through can be derived by the amount of heat energy taken away from the wire.

Audi is drawing cool air by running a duct from the top of the front grill to the air filter box, which suppose to draw the coolest air possible. What I found was, after hours of driving, heat from the engine started to heat up the air duct, as well as the air mass sensor (made of aluminium). The housing of the air mass sensor is especially hot, hurt if touch (must be over 90 deg C). Theoretically, this external heat would affect air mass measurement which mistakenly assume higher air temperature due to hotter housing, result in overly-lean air-fuel mixture. I can feel it, I think you can too, when you start driving when the engine is cool, you feel better response and the car is more torqy. After some time (30 minutes, maybe, on high speed), especially in hot summer afternoon, you would feel the car become less powerful. But in actual fact, temperature of the external air drawn are both approximately the same.

What I did was to wrap the air sensor housing with thick cloth to act as heat insulator. Amazing, I have that "morning power" feel all along the journey!! Kick down is more responsive on high speed. I guess Audi control kick down when the engine is too hot to avoid over loading. And the sensor housing was just a little warm when touch (may be 40 deg C), but the air hose is still very hot, taking heat rediation from the engine.

I went further to insulate the whole air induction system, including the air filter housing - they are black in color and prone to absorb more heat. It feel a little better after that, but not as much as after I insulate the air mass sensor.

You should try it. It cost you almost nothing. I did not have the mean to measure actual output change, but the power improvement feel is quite apparent.