YW,
I am NOT an automotive engineer, but I have seen and attempted to work with the very complex calculations involved....and lemme tell ya, EVERYTHING is involved...
Cam profile, timing, volumetric efficiency (intakes etc) exhaust design...combustion chamber shape and where in that, the spark plug sits.....flame path.
it ALL has an effect on the other. Just the equasion for a genuine exhaust header is more math than most people are capable of doing correctly. I've seen it, tried to use it, and got lost. I learned to trust engineering and beware of marketing.
In the physical world, as much as we know what should be, we have to understand that it sometimes simply is'nt. Thats the best way that I can describe how the aspiration of a gas engine works. Increase runner length and you WILL gain stump pulling low end torque. Shorten runner length and you enable the engine to breath at the faster cycle rate (hi-rpm).You don;t get both. Compromise is the art of balance.
Plenums have limits as they are the byproduct of the engine displacement to a large degree. The best thing to do to a plenum is to make it efficient by grinding away casting ridges and rough edges inside the runner ports. Polishing is kind of a myth in gas engines. There is a "boundry layer" that hugs the surface of all the intake parts whether it be silky smooth or rough as a cobb. "Porting" just works to increase the efficiency of the passage, not demanding it to be smooth. One secret to efficiency is equal volume in runners and ports. CC'ing heads is well known. CC'ing intakes is what pro's do. When all cylinders are treated equally, the crankshaft is the benificiary. One cyl stronger than the remaining also means that there are 7 that are weaker than 1.
Yes, I remember many of the old carbed motors with multiple carbs....BUT, we accepted horrible fuel/air ratios back then and those old motors had very different cam profiles that were not the least bit concerned with the exhaust gas being full of unburned fuel during much of the rpm band. Heck, add a few % more fuel to your existing air and you;ll see some dramatic power increases. You;ll also see another motor thats ready for complete overhaul at 100,000 miles instead of the 200,000+ that we get now because of precision fuel/air management....
Extra gasoline washes the lubrication off internal parts, like cyl walls. It makes more power, but its de-lubing the motor at the same time. Poor trade off at $3 a gallon and the cost of rebuilding.
If you ever get the chance, look at something like a a Ferrarri and one carb per cyl. But, it also has radically different intake design with valves nearly as big as the piston, and other extremely different engine parameters. They design for pure power and its usually ALL upper rpm range. A motor like that will load up and foul the plugs under 6000 rpm....its only efficient when its screaming, unlike more common designs made to be more user friendly and work at a wider range of rpm.
I learned engine theory from 2 strokes in MX bikes and some drag bikes many yrs ago that would spin 12,000 rpm stock but only had usable power in a window of about 2000 rpm.. WHen I got into cars and big 4 strokes it was no longer about rpm, but things like engine mass, internal weight, etc.... 4 strokes are much more complex because of more moving parts. In a 2 stroke it was 100% wave efficiency and that had help with the way a 2 stroke works and the dual action of its pistons.
Strangest thing I saw was an inline 6 with a big trashcan size 4bbl sitting on the side of the block. Factory Pontiac Firebird.
Hope this helps....its the extent of my knowledge !
As to the one for one with displacement - that sounds waaaaay too easy.
