hmmmm........nice choice of discussion!!!
Its not something ive ever thought of looking at before, and all we can apply are 2 stroke tuning theory and the basics of pulse tuning.
pipe 2 should flow more than pipe 1 since flow at any pressure is directly related to oriface size. But pipe 2 has constant laminar flow with no pressure changes and risks of flow separation and changes in skin friction.
There is no way i can offer a definite answer as my understandings of such aerodynamic, flow boundary theory is too limited to actually propose a credible theory. lol
But as far as i see it you have several problems with flat faced restrictor plates. Firstly is the effects on pure flow. As flow reaches a restriction is passes through, increase speed and experiences a pressure drop, a venturi effect based on Bernoullis principals. The area directly behind the hole would be low pressure and the area directly in teh middle of the hole would be of higher pressure due to poor flow entry profiles. With a simple open oriface with no taper or ram profile the gas flows around the edge and due to the compressability of gasses it makes a higher pressure centre of the hole which reduces flow. You will get flow separation (creating many random and detrimental flow pattern changes and pressure changes) behind the restriction forming turbulent boundary flow and eddies under the boundary surface, youll have a much broader velocity profile and the boundary layer thicknes will incrase, then continuing with high sheer stressses before the nxt restriciton depending on length and time to settle.
Then we have to take into account the pulse nature of exhaust gas motion, where slugs travel along the path. The slug is formed of a hig pressure head, and ambient pressure centre and a below ambient pressue area at the rear, which the nxt high pressure head of the next slug follows. This will greatly affect flow patterns through the hole and the speed/temp/viscosity will affect the random nature of eddies behind the restriction. And being random we cant predict it (yet....if ever lol).
Then along with exhasut gas pulses you get pressure waves which travel at the speed of sound through the exhasut system. Speed of sound varies with temperature and density. These pressure waves will be reflected by the edge of the restriction and head back up the system to the exhasut valves and cylinders and can severely mess up exhasut tuning. The wave will be a an exact positive reflection. However, part of the wave will pass through the oriface and the nature of these waves and pulse tuning you get a negative refraction and sign change due to the change in crossectional area. This again will head up the exhasut system to the cylinder. And due to the minimal section change the wave sign is hard to predice where an exact negative sign would be the result of an infinate and instant crossectional change (tube to atmosphere essentially) and tuners take this into account as its more predictable. You will get odd pressure and pulse waves returning to the cylinder and some might help scavenge, some might push fresh charge back out the inlet o overlap, who knows what will happen.
A million and one otehr things will be going on and i really dont have the brain beans to think about it all now lol, or ever.
Sure, this all applies to a high budget tuned engine where every last factor is taken into account, but manufactueres spend ALOT of time getting this sort of stuff to the right compramise as std........and i personally cant see it helping your engine in any particular way.
Put simply, performance engines dont want to see a back pressure, its not needed, its an old theory applied to mainly carbed cars where the benefit can be seen (just).....back pressure, jsut get rid of it.
pipe 2.....theres less to think about lol!
