swampbuggy wrote: ↑
Sun May 13, 2018 9:58 pm
Warpspeed---The CSA and or the MCSA (Minimum Cross Sectional Area) have to be designed or sized to get the air SPEED about where it is needed to be when the engine is at full song, is this correct ? Mark H.
Yes and no
Again this is more about porting
You do not control airspeed in a engine if you change the cross section the rpm will change to balance it out....
when porting you need to look at airspeed more inline with how the port is moving the air and where it is heading if the airspeed is too high as you head into the short turn it will not make the turn ...a lot of times when you open up the cross section just before the turn the flow will only change a little but the quality goes up ...
Years ago I remember seeing a diagram of a bubble on turns in a pipe and it stating that's what it took to maintain the speed in the turn .. always stuck with me
Minimum cross section is more about what you need to move the air ... one of the problems with porting is the work to put back something you cut to big so in a problem spot it helps to know how much you need to open up ... I have one here now that I need to push the pinch point back .120 but sonic checking says there is only .126 in the wall ... knowing what I need let's me plan how to get there
From a HP standpoint the flow is what you need to make the power as long as the port is stable .... with that said there is a fine balance on cross section you make it big enough to move the air clean but not so big that at low rpm or part throttle it's sluggish ... some of the old Ford heads where really bad about to much cross section to much cc you had to fill it to make it work
The math part of cross section is a little different then the flow work on the bench