Ok I want to roughly calculate Mass of Air into my otherwise stock 95Z LT1 and then compare it with my MAF scanned results.. @ WOT.

Does anyone have the formula?


I caught my car pulling 14* of knock retard once and I think my MAF readings were kind of low when it happened. (Low for the RPMS and MAP readings that its).

I am suspecting the MAF or MAP or Coolant Temp Sensor or all of them for variuos reasons.

Can anyone help? My calculations from that one reading suggest that *if* I were to rev her up to 5500 RPMs under the same exact load my car would ingest up to 206 grams per second/or 27.25 lbs per minute of air.

I was expecting more like 250 to 270 grams per second/ or somewhere between 32 to 36 pounds per minute. My car has a new Air Filter so no restriction there.

I need a good formula that includes air temp/Bar/RPMS/engine size.... and whatever you can throw in for acuracy.

thanks

Marvin

 

I found this formula from a post.

Is this the formula I am looking for? if so then what units of measurement are being used?

Is engine Displacement in cubic inches? Liters??
whats the gas law constant? I need the whole thing to make this formula work. Anyone know about this?


Marvin

 

The easiest thing to do is work in in cubic inches, multiply engine displacement (e.g. - 350 cubic inches) by RPM/2 = cubic inches per minute. Convert that to cubic ft per minute (divide by 1,728). Then multiply by VE. Now you have actual airflow on a volume basis.

To convert to "mass flow", it is easiest to take the density of air at a know absolute temperature and pressure, and prorate the density to the actual conditions. For example, the density of air is 0.0808 #/CF at 492degR (32degF) and an absolute pressure of 29.92"Hg.

0.0808 X (MAP/29.92) X (492/(IAT+460)) = density at actual conditions.

Then multiply density in #/CF X CF/MIN to get #/MIN.

For 5,500RPM on a 350ci engine, air flow at 100% VE would be 557CF/MIN. At 80% VE, it would only be 445.6CF/MIN. At 32degF and 29.92"Hg, mass air flow would be:

445.6 X 0.0808 = 36.0#/MIN = 272Gr/SEC

If you were to run the engine at 80degF (540degR) and 29"Hg, mass air flow would be reduced to 31.8#/MIN = 240GR/SEC

I can send you a spreadsheet that summarizes all this, if you want.

 

ABSOLUTELY YES!!! please send it to me.

MRivera982@Yahoo.com


Fred that was one solid answer, thank you Sir.


Marvin

 

I am assuming you mean "multiply Engine CID" by RPM/2 =cubic inches per minute?

as in (350cid x (RPM/2)) / 1728 then multiply by VE?


Example (350CID x 5500) / 3456 = 557 cubic feet/min... then

if my best VE is 85% my final answer is.... (557 x .85) = 473.45?


That sounds about right....doesnt it?


I will figure the rest later on tomorrow..


Thanks again.

Marvin

 

Injuneer, I received the spreadsheet. Thank you so very much.

I still havent been able to see it though. I have Microsoft works and when I try to open it it tells me its password protected. that I should open it with the program that created it... remove the password then save it, before I attempt to open it with Microsoft Works.


Marvin

 

It's an Excel spreadsheet, with the "normal" Excel password protection to prevent people from altering anything but the "user data" fields. Not sure how to overcome the limit of MS Works.

Fred

 

Thanks Fred.. I will eventually crack the code or my head in the process.

thank you for your help

Marvin