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Message: <blockquote data-quote="f8." data-source="post: 107792" data-attributes="member: 541">firstly, dolly, thank you :Dhi jun9970,when you say amount of air flowed=xyz, i wasn't quite able to understand you. is x the diameter of the port? if so, i can't see it still how xyz is amount of air flowed.anyway, lets say amount of air is the mass of air, because that is independent of pressure then unlike volume. and this amount i call n.i mentioned previously in some old old post, quoting ideal gas law from form 5 spm physics, thatPV=nRTwhere P is pressure, V is volume, n is number of moles of the air molecules, R is the ideal gas constant and T is absolute temperature.our issue here is slightly complicated by the time dimension cos we are dealing with flow rates and velocity. anyway, in this case, the only time varying variables are P, V and n. T of course changes over large scale time, but in the small scale time during valve open and shutting its P and n that varies.so fluctuating V in time, is your CFM then.man answering this is going to take all day to explain properly. and i haven't even got to my point yet. i think i'll come back to answer this better another time.all i want to say is, if bigger is indeed better, lets forget having exhaust pipes then. just leave the exhaust ports exposed. will you get more power? surely there is less restriction than feeding it into a pipe.just bear in mind air is a fluid. and moving fluid has momentum energy because it has mass and thus inertia. once you establish a high flow of gas, it will tend to want to continue rather than stop. and because your engine releases gas and takes in gas in pulses, it really helps when during the interval between pulses, there is still remnant gas flow rate from the previous pulse before the next one comes. this helps to smooth out the pulsing a bit, so that the gas doesn't have to be accelerated and deccelerated each time so much. and very high gas flow velocities help. of course, as with everything, too much of it is bad. in this case, when the flow starts becoming turbulent, its bad. so the trick is to size the ports big enough for least restriction yet small enough for high velocities.and i think the VR4 head ports are a tad too big for a 2L doing 300-400hp, in which case the evo heads might give better response, promote faster burn rates which will give more power with less ignition advance, promote better mix and actually end up squeezing more air in due to higher air flow velocities.go speak to any racing motorcycle tuner and they will tell you all about the beauty of small ports.</blockquote>

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