Back Pressure

[armthelaser]

I was wondering if you really need back pressure? If it is from a cat, muffler, or resonator or is some needed for any purpose at all?

[AJ]

Backpressure is a restriction but it's not a yes or no question. It all basically deals with exhaust gasses and exhaust diameter and exhaust flow. And there is differences between NA cars and cars with Forced induction like a turbo or supercharger. The goal with Turbo DSMs is to have good free flowing exhaust which will benifit the turbo. Sometimes you can go to big. It's said to not use anything less than 2.5" exhaust on a turbo car (or it's suggested), but that also changes with some of the differances in engies. That cubic inch crap which I won't get into cause I don't know.

[JET]

AJ is right, on a turbo car you can't go too big because the turbo causes back pressure. A N/A car is a different story.

[Slwlasr]

Turbo cars = minimal backpressure
NA cars = some backpressure needed

[Shane@DBPerformance]

For part throttle daily driving back pressure helps give the feel of some low end torque, you can feel the difference between 2.5" and 3" at low throttle on a DSM. At WOT, the less exhaust the better.

[Wizard]

The big thing with backpressure on a NA car is exhaust flow out of the combustion chamber once the valve is opened, and when the 2 cams overlap (both valves slightly open to purge the chamber of burnt gasses). Too little backpressure on a NA car will also burn valves. This is mostly from sucking cold air back in thru the exhaust. Hot exhaust valves don't like cold air. A turbo car doesn't have to worry about that. Kind of impossible to get cold air back to the exhaust valves past a spinngin red hot turbine wheel.

Wiz