[JR429]

Originally Posted by Eric@AMS

just so you know losing back pressure on a turbo car will NOT cause you to lose power. Back pressure causes a turbo to not spin as efficiently which can in turn hurt performance. Your friend sounds like he is applying NA engine theory to Forced induction engine theory and you can't do that.

This is not true. Depending on the specific application there are substantial differences in the power curve as a direct result of exhaust back pressure. There are over a dozen different variables that can cause this scenario including turbine nozzle area, turbine wheel design, exhaust pulse timing, pre / post turbine pressures, and of course more basic exhaust system design.

I think the fundamental picture you are missing is that exhaust back pressure can be negative as a result of exhaust gas cooling and escape velocity.

I have personally witnessed dozens of instances where torque losses have occured as a result of decreases in exhaust back pressure on turbo cars....

[scheherazade]

Originally Posted by Former_Boosted_IS

Why in the world would you do that other than weight savings. Remember flow is proportional to cross section area. The cross sectional area for 3" versus dual 2.5" is:

Single 3" = 7.1 sq. inches
Dual 2.5" = 4.9 sq. inches + 4.9 sq. inches = 9.8 sq. inches

The bottom line is a dual 2.5" exhaust flow the equivelant of a single 3.5" exhaust. That is a big pipe.

Yes, but given the *same cross section area*, you want the least amount of circumference.

Wall-friction is a significant source of drag for the airflow.

-scheherazade