Headers vs. Exhaust Manifolds ~ 'Let The Debate Begin'

'Exhaust Restriction 101'

Back-Pressure > Will negatively effect Engine Performance.

Increased 'back-pressure' levels, will effect the internal combustion.
The Engine has to compress the Exhaust Gasses to a higher pressure,
which involves 'mechanical work', which equates to more fuel consumption
and higher exhaust temperatures.

Even the 'slightest' improvement in reducing Back-Pressure, will increase
Horsepower {2% to 3%} in a 'stock' Mopar 340.

Using the general factor of a 'stock' Mopar 340 {290 Horsepower @ 5150 RPM's}.

That comes to {5.8 to 7.7} in Horsepower gain.