Carbon monoxide, my ass.
4 seconds sound clip from the Days of Thunder movie soundboard.
You can hear this line at 01:23:47 in the Blu-ray version of the movie.
Quote context
[...]
- NASCAR privately claimed the setup on the car is what killed Buddy.
- You used thin-walled tubing to keep the weight down.
- The exhaust fumes broke through the fire wall and carbon monoxide knocked Buddy out.
- That was the loudest-talking unconscious man you ever heard in your life.
- Nothing killed Buddy but his imagination.
- Why didn't you let them investigate, Harry? Why? Why?
- 'Cause I should have known better than to let him drive in the first place.
[...]