Sal R.

Can someone please explain the pro & cons of having equal or unequal length runners on exhaust manifolds for a turbo application and headers for NA cars? Don't understand the deal behind that reasoning. TIA

1-BAR

there are a bunch of sites on the net that will give you a full technical report of how it produces more power.

Pat-SoCal

NA motors have similar headers available because somebody found that when you get the individual puffs to evacuate the header one at a time, instead of having all cylinders trying to exit the header at once (congested), the exhaust flows much more freely. I believe that the reason for doing this on a turbo application is to separate the exhaust puffs to optimize the rpm of the impeller.

Bollinger

As used on the MR2. Never completely merges the exhaust from all 4 cylinders until inside the turbo. This is supposed to preserve the puffs which help drive the turbine instead of a smoother air delivery with lower peak air speeds.

Puffs are more effective because turbines are less efficient at lower flow rates since the air's "ability" to find its way around the turbine blades instead of pushing on them increases as the air slows.

Bollinger

scavenging refers to air flow through cylinders, not turbos