i was just thinking... you know how an intake manifold is supposed to be of a specific design to optimize cylinder filling and efficiency? like, the intake plenum volume is supposed to be anywhere from 50% to 75% of the total engine's displacment? it essentially acts as a big resivoir of air for the engine to draw from when the throttle is tipped open. this would prevent the scenario of hand-to-mouth feeding of the cylinders. all the air that the cylinders need to injest is conveniently stored in the intake plenum. so, this way, it doesnt have to count on the air inside the IC pipe to fill the cylinder.
what if the exhaust manifold was of a tuned/specific volume? i know that typically a tuned length runner system on an exhaust manifold is pointless on a turbo setup. since there is so much backpressure in the manifold, resonant tuning is virtually non-beneficial. however, i think it would be benficial if the exhaust manifold runners had a total internal displacement equal to or greater than the swept volume of that specific cylinder. for instance, our cylinders are about 500mm2, not including the dish of the piston and the combustion chamber. wouldnt it be helpful if that 500mm3 of exhaust gas volume had someplace to go and not be constricted/restricted?
i figured, if i had an manifold runner diameter of 1.75" ID, i would have about 61mm2 of cross sectional area. in order for my exhaust runner to be able to accomodate 500mm3 of exhaust gas volume, it would need to be about 8.1" long. of course, this is a rough estimate considering that the exhaust gas volume is under pressure and thermal changes and will expand greatly once released into a considerably less restrictive chamber as compared to a cylinder bore. so, 500mm3 of gas can expand exponentially when its unrestricted and has a temperature increase of almost 2000*F on the exhaust stroke.
it may be a moot point seeing as how even an exhaust runner of 500mm3 internal volume probably wouldnt be able to accomodate one cylinder's exhausting of gasses due to the significant expansion rate when taking into account the extreme temperature change. but i figure if i keep the exhaust runner voluem at least equal to the cylinder volume, itll be less restrictive than shorter runners, smaller runners or even a log manifold. if i could figure out which forumla to use and how to work it, i could calculate approximately HOW much more volume a 500mm3 cylinder's worth of superheated exhaust gas would take up and then get an idea of what size a runner should be to accomodate this gas volume.
im sure some people will say, whats the point, it doesnt matter. log manifolds work just fine and they dont hold a full cylinder's worth of air. or, if the runners are too voluminous, the turbo would be laggy as the gas could stall in the runner once it is filled. it may become stagnant as it waits for the next exhaust pulse to push it through the runner. its just an idea i was toying with, because i plan to make my own manifold, but just not exactly sure how long i should make the runners and if there would be any sort of differance between a short and long runners.
feel free to talk amongst yourselves.
what if the exhaust manifold was of a tuned/specific volume? i know that typically a tuned length runner system on an exhaust manifold is pointless on a turbo setup. since there is so much backpressure in the manifold, resonant tuning is virtually non-beneficial. however, i think it would be benficial if the exhaust manifold runners had a total internal displacement equal to or greater than the swept volume of that specific cylinder. for instance, our cylinders are about 500mm2, not including the dish of the piston and the combustion chamber. wouldnt it be helpful if that 500mm3 of exhaust gas volume had someplace to go and not be constricted/restricted?
i figured, if i had an manifold runner diameter of 1.75" ID, i would have about 61mm2 of cross sectional area. in order for my exhaust runner to be able to accomodate 500mm3 of exhaust gas volume, it would need to be about 8.1" long. of course, this is a rough estimate considering that the exhaust gas volume is under pressure and thermal changes and will expand greatly once released into a considerably less restrictive chamber as compared to a cylinder bore. so, 500mm3 of gas can expand exponentially when its unrestricted and has a temperature increase of almost 2000*F on the exhaust stroke.
it may be a moot point seeing as how even an exhaust runner of 500mm3 internal volume probably wouldnt be able to accomodate one cylinder's exhausting of gasses due to the significant expansion rate when taking into account the extreme temperature change. but i figure if i keep the exhaust runner voluem at least equal to the cylinder volume, itll be less restrictive than shorter runners, smaller runners or even a log manifold. if i could figure out which forumla to use and how to work it, i could calculate approximately HOW much more volume a 500mm3 cylinder's worth of superheated exhaust gas would take up and then get an idea of what size a runner should be to accomodate this gas volume.
im sure some people will say, whats the point, it doesnt matter. log manifolds work just fine and they dont hold a full cylinder's worth of air. or, if the runners are too voluminous, the turbo would be laggy as the gas could stall in the runner once it is filled. it may become stagnant as it waits for the next exhaust pulse to push it through the runner. its just an idea i was toying with, because i plan to make my own manifold, but just not exactly sure how long i should make the runners and if there would be any sort of differance between a short and long runners.
feel free to talk amongst yourselves.
(simular to your idea just post turbo)