Another S/C'd member worried about his AFR

[dallas]

Backpressure does not create exhaust gas velocity, if the pipe diameter is too big the air moving down the pipe slows down and cools down which in turn makes the air molecules less active slowing down the flow. The reason race cars don't release at the exhaust port is because exhaust velocity actualy help draw air out of the cylinder head, but to get that you need the right diameter and length of pipe to create the exhaust velocity, what you don't want is any back pressure to slow down the flow, You have the right idea just not the right terminology, there are some really good papers on exhaust design and performance done by ASTM I belive, that tell you exactly that.

Originally Posted by HTM Yaris

Back pressure is a good thing . Some not alot . Without Backpressure(BP) there isn't any exhaust gas velocity . If no BP was a good thing all the real race cars would have exhaust gas being released straight from the exhaust port . ( Yes I realize that exhaust pipes also evacuate heat )


Try this , go turn on your garden hose . See how it flows ? To increase the velocity of the flow you can do 2 things 1. increase the volume of water or 2. partially cover the end of the hose with your thumb (creating BP) .