So after years ive finally gotten alot of problems fixed on my gf 92 camaro (5.0) and have been driving it a decent amount. Ive always noticed crawling at low speeds i could smell a bit of exhaust smell inside I honestly figured it was because it smokes like a train from burning oil because its extremely high miles. Lately ive noticed with the windows down at highway speeds 55-70mph after letting out of the gas and getting back on it I can smell them even going that fast. Problem is even as much as it smokes I cannnot pinpoint where its coming from. MY camaro with open element has the open crank case breather and with vents blowing in town I can smell just a hint of fumes, with her car I cannot smell anything with vents blowing period but only with windows down. even laying in the engine bay I can only barely smell just a hint but not sure how much of that is coming out the back of the pipes. Any advice on how to track down a leak like this? im thinking around the cat or y pipe but just can tell exactly where it is.

 

More than likely its either the gasket at the AC box or someone has drilled holes below the AC box for speaker wires etc. Combine that with the open breather and probably header leaks. Also these cars have a very low coefficient of drag. By design a small boundary layer of air forms around the car at speed, this can cause exhaust to pull from under or even behind the car into the windows when they are down as the window being down breaks the flow and causes buffeting.

Look where your AC lines go into the box on the firewall there is foam weather stripping in there that is probably dust at this point, there is also a seal where the top joins the box, and where the box mounts to the wall.

The donut gasket where the headers meet the y-pipe or header to head gasket is likely leaking.

 

Hers doesnt have open element yet its still just stock air box, But what you said about coeffiiciency makes sense, In my mind it would have to be a low leak to only smell with windows down. I did look around in the engine bay again today and I noticed one time I reved it some smoke fumes rise from the back of the engine, just a bit though. I dont think it came from the head though. Gonna look at the y pipe again soon.