http://forum.mazda6club.com/index.php?act=ST&f=18&t=47827&st=15#entry616641
Anybody want to chime in… Provide some info that will set the record straight?
i take it your “litleeffer”?? it looks to me like you are both kinda right/wrong…you have the calculations right, but im not knowledgeable enough to give a straight answer, but after reading all of that it seems to me that one of you is talking about the CFM the turbo sucks in, while the other is talking about how much air it forced out. needs more clarity, im sure zerodaze will chime in and straighten it out for ya
Zer0DazE is gonna be ecstatic, he’s famous on the Mazda forums… Hahaha…
Anyway, to answer your question ZD’s calculations are spot on as well as his process…
uhm you know CFm is volumetric flow has has very little to do with how much mass(density) is flowing past a specific point. Higher pressure=higher mass flow. 1 cubic foot of air will always equal one cubic foot of air
Thats what I was saying. A turbo rated in CFM is done at STP. Which can be converted to Mass density at STP.
The basic premise of the arguement is that the engine will take in more than 264 CFM at STP when boost is involved.
no it wont, it will always be the same CFM as it is a rigid tank, will take more air mass but not acutal volume. that is unless you are speeding the engine up or increase the linear air speed into the motor, than the CFM will increase, but if you are flowing the same linear air speed into a rigid tank pressure does not matter it will still fit X ft^3 per minute of sucking. Volumetric flow is independent of Mass flow to a point. You can cahnge the density of the fluid, not change the overall volume, the volumetric flow will stay the same. Aturbo rated to flow 264Cfm will always flow 264Cfm, the mass flow rate of it will change if the pressure is increased or decreased since air is compresable.
Image this to be a water system, flowing at 264CFM, that is 264 cubic feet of water past a specific point in the line in every minute. Put it under high pressure, 300psi for sake of the argument, keep the linear flow speed the same. You are still flowing 264cubic feet of water pass that specific point every minute
Your statement is absolutely positively Right, thats why I said STP which is Standard Temprature and Pressure. Which is what corrected CFM values on some compressor maps are based on.
Which is scientificly defined as 1 atm at 0 degrees celcius.
http://www.ilpi.com/msds/ref/stp.html
The point that I was disputing is the inference that was made on the MS forum that the flow rate of the turbo need not be over 264 CFM.
A claim was made that if the turbo flowed 366 CFM then there would be plenty of room for the turbo to support boost at 15.7 PSI at redline which I attempted to prove false.
The premise of my arguement was that just because the motor can only take in 264 CFM does not mean the turbo does not need more than that.
But I understand what you are saying. But, if you compress the charge it is no longer at STP.
yes you are right, i guess i got confused by the way that the previous statements where presented