kinda sorta..... that was sorta the case back when cars had exhaust manifolds instead of headers. it wasnt that the car ran better /w backpressure. it was that suction helped the gases move away from the cyl ports faster. i dunno why people insist that 'backpressure makes the car run better'. if that were true, we woudlnt have exhaust at all and our engines would explode the idea of suction created through smaller exhaust piping is to REDUCE backpressure in a manifold exhaust system. ill discribe how it was then, and how it is now. get ready for the essay

then: the exhaust manifold days. the engine exhaust ports (1 per cyl) dumped into a big chamber (the exhaust manifold) which had a hole that connected to the exhaust system. so picture a box /w 4 ports feeding in one one side and 1 port draining on the other. its like a room /w people running in 4 different doors and fighting to get out 1 door. so you have a high pressure pulse (the exhaut) coming form the port and expanding in this chamber. it would just kinda chill there. a little bit, the next pulse would would come from a different cyl, and expand in the chamber as well. each time this happens, the pressure in the chamber increases. as the pressure increases, its harder and harder for the gases in each pulse to move outa the cyl into this chamber. once it gets too crowded (too much pressure) gasses start getting forced out the exhaust hole into the exhaust system piping and away from the car. the higher the pressure, the faster this happens. however, the higher the pressure, the harder it is for the engine to get rid of the exhaust! it has to push all the other exhaust outa the way! the pressure always starts out low in the exhaust manifold, then builds up as the engine speeds up. the exhaust literally needed to be forced outa the way for the engine to run.
to combat this, the exhaust system itself was made small enough so that when the first pulse of exghaust finally gets forced through the exhaust, its pressurized due to the smaller path and created a suction (vacuum) behind it to force the next pulse to follow it. and that following pulse does the same to the pulse behind it and so on until there is a negative pressure in the exhaust manifold and gases start flowing more easily. now as soon as a pulse comes outa the cyl, its sucked right outa the exhaust hole on the other side of the manifold due to this vacuum. the engine has to do 0 work to push the exhuast out and the world is a happier place =)

however, this worked against itself. that is, with huge huge pipes, its very hard for the pressure to get high enough to cause any issues. but big pipes cost more $ and make the exhaust louder. so the goal was to stay cheap and not annoy every other car on the road

now: exhaust header days (sounda dirty, huh): how each exhaust port from the cyl has its private own direct path to the exhaust system. we dont have to worry about pressure building up in it or any of that mess. when a cyl releases its exhaust, the pressure is pretty much constant as it hits the header run assigned to that cyl, because the diamater of the run is about the same as the diamater of the cyl. to exhaut pipe as a whole is a bit larger, so to equalize to the regular pressure, this exhaust pulse moves to the exhaust area and the pressure drops. after a few pulses build out outside of the header, the start pushing each other down the exhaust tube and outa the car. now the pressure in that header run is also normalized and very low. so we never have the same problem of having an increased presure preventing an exhaust pulse from existing the cyl, unless we have a restriction somewhere further down the exhaust system (such as the downpipe, cat or muffler). in our car, we have 4 exhaust header runs for the 4 cyls. so even with restrictions, every pulse of exhaust will only create 1/4 the back pressure we would have had in the old design, which is because we divided by the 4 cyls header runs.

that said, a bit of suction will still help gases from buliding up in the restrictive areas, like the downpipe in our car. however, its not as big an issue. i keep telling people, set a realistic goal of where you want to take ur car and plan ur exhaust according to the final.

 

Didnt an EVO guy try that and melt his side skirt?

 

Thanks for the info blk-majik. I guess all this volumetric efficiency thing is waaayyyy more difficult than I thought. lol