Thanks Everybody.
Vacuum Gauge is already planned. Think next weekend.
And also some aero mods at the front. I need some 0.5mm plastic plate but don't now were to find it.
But i have some questions what would be more effective. See picture below (my best drawing skills in The Gimp). Left you see a closed front, like that from AdrewJ's 5th Generation Civic
photo. And on the right side i thought about a kind of spoiler behind the bumper pressing the air under the car.
Now i friend said the less air under the car the more effective it is. So it would be solution on the left side. But i thing that i have more counter-pressure (don't know if this is the right word or should it be "Drag"), so the solution on the right side would give less counter-pressure.
So what to do?
/edit: About the Vacuum Gauge. I was in a shop here en they have some like going from -1 to 0, and all i found here on the forum go from 30 to 0. What's the difference?