Quote Originally Posted by Sport20
So how do i Get more back pressure to make more low end power?
I guess you didn't read any of that?

You don't want to increase "back pressure" to make low end torque, you want to increase the pressure drop at low RPM. You have to make an exhaust selection based on where you want your power though, as your car will flow less air at 1000 RPM than it will at 6000 RPM. Therfore if you have an exhaust selected based on 6000 RPM worth of exhaust gasses, your pressure change at 1000 RPM will be greatly reduced..

Read the entire article again if you don't understand with emphasis on this portion.

Quote Originally Posted by stealthrt
The effect of having larger exhaust pipe diameters (in the primary, secondary, collector and cat-back exhaust tubes) has a direct effect on gas velocity and therefore delta P (as well as backpressure levels). The larger the exhaust diameter, the slower the exhaust gasses end up going for a given amount of airflow. Now the ***** of all this tech is that one exhaust size will not work over a large RPM range, so we are left with trying to find the best compromise in sizing for good low RPM velocity without hindering higher RPM flow ability. It doesn't take a rocket scientist to understand that an engine flows a whole lot more air at 6000 RPM than at 1000 RPM, and so it also makes sense that one single pipe diameter isn't going to achieve optimal gas velocity and pressure at both these RPM points, given the need to flow such varying volumes.

These concepts are why larger exhaust piping works well for high RPM power but hurts low RPM power; because is hurts gas velocity and therefore delta P at low RPM. At higher RPM however, the larger piping lets the engine breath well without having the exhaust gasses get bundled up in the system, which would produce high levels of backpressure and therefore hurt flow. Remember, managing airflow in engines is mainly about three things; maintaining laminar flow and good charge velocity, and doing both of those with varying volumes of air. Ok, so now that all this has been explained, let's cover one last concept (sorry this is getting so long, but it takes time to explain things in straight text!).