Fuel Efficiency differences 870 vs 871

[Rawze]

I think your over-thinking it a bit there.

Last I checked, there was hot inert gases and and an EGR valve restricting flow though the venturi portion getting in the way of that effect, therefore there is no real efficiency gain. Block the EGR pipe (just commenting on what most 870 owners do) and all you end up with is a bit of unnecessary turbulence.

(speculating here) ...
The most likely reason that newer engines do not use a full Venturi pipe design like the 870 has is the fact that exhaust manifold pressure is almost always much higher than the intake pressure because of turbocharger inefficiency. There really is no need to "suck" the air from the exhaust into the intake by very much, it mostly wants to go that direction any ways.