Originally Posted by CandymanGT
My favorite "idiot identifier" is people who try to tell people then need a little back pressure in their exhaust...
Sent from my iPhone using Mustang Evolution
i think this "backpressure" myth got started with a game of telephone and people inaccurately regurgitating info.
Negative pressure, caused by a trough behind pressure peaks is what makes exhausts flow advantageously when compared to being pushed right out into atmospheric pressure air. The exhaust tube acts just like a siphon in the way that it uses exhaust charges to pull other exhaust charges out.
I think that this negative pressure concept actually got misunderstood as "back pressure" aka possible reverse flow, or just exhaust flow interference. Which clearly doesn't make sense for evacuating exhaust in a 4 cycle engine.
The only engines that benefit from reverse flow of pressure from exhaust is a 2 cycle engine, and that is only because fresh fuel:air actually enters the exhaust port for a brief moment. Thats why 2 strokes use an expansion chamber. When the exhaust charge hits the constricting cone, a wave of pressure is sent backwards, which puts the escaping portion of fuel&air back into the engine.