With a stock setup, a little CO gets in the cabin.

It's probably a lot worse with that, especially since a race engine produces a thousands times more CO than stock engine.

especially a rotary burning oil like an efficient 2 stroke :)
I remember the days of always getting pulled over on my 13bp R100 and as the 3 mufflers didnt kill the blood curdling brap till I put the death shriek supertrapp, sounded like horrible vibrating tin.