DigitalFusion

Hey, again...

I was reading blueshadows archived post about reading compressor maps, and in section 2, he explains that you need to calculate your engines air flow rate and convert it from CFM to lbs/min.

After finsihing the article, I did several searches on calculating air flow rate, air flow rate, etc, and came up with nothing.

So, how do you calculate your engines air flow rate? I wanna be able to read these damn maps! lol

int3gra

Most of the questions you have been asking lately are covered in Maximum Boost by Corky Bell. Its one of the best investments you can make. Its the turbo bible.

ps. buy one for each washroom

DigitalFusion

ok.. i get this part:

(RPM*(displacement in liters*61.023744)/3456 = CFM theoretical

(1 ltr = 61.023744 Cubic Inches)

BUT, u need air flow under boost, so...

(WHAT THE HELL DO I DO HERE??????)

THEN convert that number (which is CFM) to Lbs/min, so i do one of these:

@ 48 degrees F : (CFM * 0.078125) = LB/MIN
@112 degrees F : (CFM * 0.070318) = LB/MIN
@175 degrees F : (CFM * 0.06251) = LB/MIN

SOMEONE HELP ME FIGIURE OUT YHE MIDDLE PART!

DigitalFusion

i ordered it the other day! i reasd it like two to three years ago but i cant remember anyting!

dbman96

Quick and dirty engine flow rate in pounds / min:

= RPM * Displacement (L) / 12964 * (boost psi + 14.6)

example 8000 RPM, 1.8L, 8psi = 25.1 lbs/min


The 12964 is just a fun little number incorporating liters/min to lbm/min conversion and the bottom half of the pressure ratio. This formula ASSUMES your intercooling system can bring the temperature back down near ambient temp.

DigitalFusion

ok, but this isnt very feasable. Could you explain the formula of how u got the 12964 number, so i coulc change it to more realistic temps, say 120 degrees?

I aint annoying the hell out of u regulars am I? Like I said, i did read the book several years ago, but cannot remember anything, so i ordered it, i just would like to be able to read compressor maps before it gets here.


I would like to be able to read these maps before the books arrives.


[Modified by CustomCockpits, 6:55 AM 6/14/2002]

BlueShadow

Hi Custom...

check out this jpeg I made a while back, I learned how to figure out engine CFM from MB, so this is how I do it.



if the pic doesn't show click the link http://www.eframes.com/ef-cgi/c/csma...compressor.JPG

I would also check around further on how to change CFM to LB/MIN, you need to find the conversion factor to find out how much one cubic feet of air weighs at XXX degrees. The conversion factors I got came from a very reliable source, but it is my ONLY source and I prefer atleast two different sources.

DigitalFusion

for the benefit of others i am hosting this pix for blue:

BlueShadow

something I should add, the VE or Volumetric Efficiency will be different from engine to engine (obviously) its up to you to figure out what the VE is for your specific engine. I have done wute a bit of research on H22 VE's and have found the the H22 has a peak VE of 102% at 7000 RPM's (1.02 in the formula), and the S2000 has a peak VE of 112% at peak HP RPM.

So I suspect that teh VTEC B18C1/5 and B16 are somewhere between 102-112% VE. Not so sure about the non-VTEC's though, those are prolly around 80-90%.

DigitalFusion

where would one begin to search to find out the VE??? i dont even know where to begin

Does this mean anything? can i somehow get the VE outta these numbers? (B16A3)

(EDIT: removed image cause its pointless)

[Modified by CustomCockpits, 1:52 PM 6/14/2002]


[Modified by CustomCockpits, 2:24 PM 6/14/2002]

BlueShadow

i just started searching http://www.yahoo.com for "prelude volumetric efficiency" and some different variations (H22, VTEC, etc), but I think I got lucky. There was a website that had an article on the S2000, that happened to mention teh S2K's VE, they also mentioned the H22's Ve for comparison.

DigitalFusion

yesh, thats what i am doing! hopefully i will get lucky

DigitalFusion

if anyone knows this, or can find where to find it (did that make sense?) I will pay them!!!!!!!