I feel intoxicated when driving (esspecially in the summer, with windows open), it's most noticeable when driving above 3,000 rpm. It smells and is intoxicating. I recently dismissed it as being from exhaust and thought it might be an oil leak leaking on hot engine and/or exhaust parts. When I'm stopped I can see how the intoxicating fumes get in my car, but when going above 140 km/h on highway how can the smell from the catalayic converter get in the car?

I'm missing one of two catalayic converters. Could the smell at high speeds be caused by missing cat. converter? It only really smells when going fast with windows open.

 

Catalytic converter usually has the rotten egg smell. If you have a small exhaust leak it is possible to have the gasses enter the cabin. When a car is traveling at a high rate of speed, an air pressure drop occurs and a partial vacuum is formed inside the car, laws of physics, same reason why airplanes fly. I would check all the joints of the exhaust system and look for pinholes. If the hardware is new tighten the clamps, I know from my own personal experience that a tiny little seepage is enough to fill the cabin. If the tail pipe is too short you can have the same problem.