Can anyone check to see if I got my math right. I wrote it from scratch. I think I posted it before, but I can't find it.
Turbocharger air use spreadsheet
Turbocharger air use spreadsheet
Turbocharger Air Flow Spreadsheet
- Thread starter McRat
- Start date
I'm confused, the spreadsheet says turbo air use, but the calcs look like you mean the maximum CFM that the engine can possibly use?
OK, call it max CFM used.
We have no throttle.
There is something wrong with this math. While it all makes math sense, we should be destroying turbochargers more than we are if it was true. I can take a GT4202R up to 140lb/min according to this sheet, yet the map goes up to 90. 50% off the map? Nope that can't be right.
Naw, 50%. I think it's the air temp or VE at high RPM that throws it off.
It seems to work for the factory charger at 20lb of boost.
It seems to work for the factory charger at 20lb of boost.
According to my notes 1 cubic ft of air is .0807 lb at Standard Temperature and Pressure.
We are dealing with IAT above 60 degrees F. This is going to throw your calcs out of wack.
We should also be seeing VE in excess of 100% in order to make the power we do.
We are dealing with IAT above 60 degrees F. This is going to throw your calcs out of wack.
We should also be seeing VE in excess of 100% in order to make the power we do.
I'm using VE as "cylinder filling". It is readily apparent that backpressure and charge restriction doesn't allow us to fully fill the cylinder with boosted air.
It shows up in our trucks stock at low boost levels.
So "VE" is a misomer. Guess it should be called something else.
Yes, it is most likely temperature causing it.
But I need some realistic temperature data to figure out what is up.
I still am struggling with collecting data off the truck, but it's entirely my fault this time.
From what I see, yours is a good approximation, no obvious errors. If you add an IAT line, you can use that MAF formula, and then divide MAF by .073 to get cfm.
atm=baro=atmospheric pressure in psi. Most of us live around 14.0 psi. (14.5 near the coast) A few of us live at 12 psi (denver, etc)
460 is just converting to absolute temperature, F to R (Rankine). 100 F=560 R. Rankine must be used if wanting to use a density ratio correction for non-standard temperature, 77 F is standard T used by Garrett IIRC.
I use .073 for standard conditions. Guy and I have different numbers I guess. He's probably right.:hug:
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