I am not sure of the exact reason for the 411 pipes having down-pointing exhaust exit ports but from my experience :
1) To stop soot spots on the garage wall, possible but petrol engines don't produce much soot.
2) To stop soot spots on the front of your caravan, possible but not many tow things with Bristol cars.
3) To reduce fumes getting back into the cabin, very possible, the aerodynamics of gases in the slipstream are weird and at certain speeds the gas might well come back around the car.
4) To reduce projected noise, most likely, as the change of direction and the small size of the final outlets make for useful reduction of the impact of exhaust noise.
People often say 'it would be worth someone making those as spare parts' and they are often wrong, but in this case, you would think that there are enough 411s around and they each need 4 pipes !
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