Originally posted by DemonSVT:
Except air flow does not work that way. Every time it is squeezed down due to a crush bend it slows down in velocity & adds more turbulence.
Repeat this process for every crush bend. Then double it for having 2 pipes. It adds up very quickly!
Actually, the exhaust speeds up in the crushes (CFM= Area x Velocity, when CFM is constant, a decrease in area {crush bend} means the velocity must be higher. [Actually, the CFM decreases as the exhaust cools and the volume of gas is reduced, but we can ignore this for this calculation, since the decrease in volume is the same for otherwise identical length exhaust systems]) .
When you increase the speed , the resistance goes up by the square law, I.E.: 2x the velocity is 4x the resistance 2^2. So the resistance goes up in a crush bend. In addition, curves (bends) mandrel or not, increase resistance. A mandrel bend (say 8 in long 90 Deg.) is probably about the same resistance as 5 to 10 times the length of straight pipe. So 8 in. mandrel bend is like 40 in. to 80. in straight pipe in resistance (This varys depending on the roughness of the wall and other factors). A crush bend is more likely a 15 to 25 times difference. This is because the increase in velocity requires energy. Resistance and velocity increases both absorb energy.
So you are right that crush bends are less efficient than mandrel. Just wanted to get the engineering right.
