the end of aroad draft tube

[IVT1]

the bottom end of a road draft tube has a slant cut, does the opening face forward or backward ?

 

[B-O-B]

to the rear

 

[40 Deluxe]

This was so a low pressure area would be created at the opening by air flow past the tube as the car was moving down the 'road'. This forward motion created a 'draft' in the crankcase to provide 'ventilation', pulling fumes out of the crankcase into the surrounding atmosphere. Modern cars use intake manifold vacuum to provide 'Positive Crankcase Ventilation' which ventilates all the time (even idling) instead of needing to be moving at 30-40 MPH (no doubt this is one reason why older cars sludged up so bad in city driving).