That's not a ventilation problem- - - -it's a clogged exhaust system. Try loosening the exhaust pipe flange at the manifold 1/2" or so and do a test drive. Another symptom will be an inability to maintain good intake manifold vacuum at steady throttle cruise.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!