# Math check = VE Calcs **URL:** \ **Category:** NYSpeed Automotive\ **Created:** [August 30, 2005, 10:12am UTC](https://forums.speedlife.net/t/math-check-ve-calcs/1902 "2005-08-30T10:12:22Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Nikuk](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/nikuk/32/7254_2.png) [@Nikuk](https://forums.speedlife.net/u/Nikuk)\ **Post date:** [August 30, 2005, 10:12am UTC](https://forums.speedlife.net/t/math-check-ve-calcs/1902/1 "2005-08-30T10:12:22Z")
The math looks good to me, but can You superenginebuilderextraordinaire’s check it for errors in theory. To figure VE of an engine in a given application, You’ll need to run a test of airflow. To keep it simple, run the engine @ 7k rpm while measuring the amount air drawn into the intake manifold (lb/min or cfm), and the temperature of the air (IAT). Now, bear with me: _Density: t1 / t2 = d2 / d1_ - t1 = temp for air of know density (32\* F @ 0.0808 lb/ft^3) in Rankin - t2 = IAT (in degrees of Absolute Rankin, F\* + 459.67) - d1 = density of air for known temperature (0.0808 lb/ft^3 @ 32\* F) - d2 = Density of intake air charge _Volumetric Flow Rate: AVF = Mfa / d2_ - AVF = Actual Vol. Flow Rate (calculated) - Mfa = Mass air flow actual (measured) - d2 = air density actual (measured) _Calculating Theoretical Max Airflow (cfm): TAF = (EDRPMVE) / (ES\*C)_ - rpm = Operating engine speed - TAF = theoretical airflow - VE = Vol. Efficiency (100% theoretical) - ED = Engine Displacement (in^3) - ES = Engine Stroke (2-stroke = 1 / 4-stroke = 2) - C = conversion factor from in^3 to ft^3 (1728) _Calculating Volumetric Efficiency: (AVF/TAF)\*100_ - VE = Vol. Efficiency (calculated) - AVF = Actual Vol. Flow Rate (calculated) (ft^3/min) - TAF = Theoretical Airflow rate (calculated) (ft^3/min) So, we have our shit tested. We come up with: **17.14** lb/min --OR-- **243.8** cfm @ **7000** RPM with our **122** (in^3) engine. The IAT was reading **72\* F**. Now, giterdone: - Density: t1 = (32+459.67) = 491.67; t2 = (IAT+459.67) = 531.67; d1 = 0.0808. So: 491.67/531.67\*.0808 = **0.0747**. - AVF: 17.14/.0747 = **229.43**. - TAF: rpm = 7000; Displacement = 122. So: (122_7000_1)/(2\*1728) = **247.11** So, 229.43/247.11 = 0.9284 or 93% VE @ 7000rpm. That about right? Thanks, -Nick ---
**Author:** ![BuickGN](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/buickgn/32/7200_2.png) [@BuickGN](https://forums.speedlife.net/u/BuickGN)\ **Post date:** [August 30, 2005, 10:41am UTC](https://forums.speedlife.net/t/math-check-ve-calcs/1902/2 "2005-08-30T10:41:38Z")
ehhh ---
**Author:** ![Nikuk](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/nikuk/32/7254_2.png) [@Nikuk](https://forums.speedlife.net/u/Nikuk)\ **Post date:** [August 30, 2005, 11:04am UTC](https://forums.speedlife.net/t/math-check-ve-calcs/1902/3 "2005-08-30T11:04:18Z")
LoL, is that a no? ---
**Author:** ![BuickGN](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/buickgn/32/7200_2.png) [@BuickGN](https://forums.speedlife.net/u/BuickGN)\ **Post date:** [August 30, 2005, 11:13am UTC](https://forums.speedlife.net/t/math-check-ve-calcs/1902/4 "2005-08-30T11:13:18Z")
yeah dude, u lost me after the work MATH ---
**Author:** ![Nikuk](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/nikuk/32/7254_2.png) [@Nikuk](https://forums.speedlife.net/u/Nikuk)\ **Post date:** [August 30, 2005, 11:35am UTC](https://forums.speedlife.net/t/math-check-ve-calcs/1902/5 "2005-08-30T11:35:01Z")
:doh: Instead of assuming all 4v motors are 95-105% efficient, I’m trying to work out a test to grasp ACTUAL efficiency. The difference in 105% & 92.5% can be HUUGGE BUFFALO, when it comes to tuning, boosting, etc. So i believe that I’ve got something that works. Requires airflow numbers, rpm numbers, and IAT. \ that’s what I get for trying.