Shep 1.8T

I couldn't find any VE % for our 1.8T that were other than guesses, and I decided for my own interest I would calculate VE under load. I just happened to use my dyno VAG COM info because I had more information about that run than any other run. ( Barometric readings, etc) So I did some digging through the archives and found this <a href="http://www.installuniversity.com/install_university/installu_articles/volumetric_efficiency/ve_computation_9.012000.htm">link</a> . I looked through the other 5~6 logs I ran on regular roads while in Colorado and I got very comparable MAF and IAT readings, so I feel it is a good representation of how the car performs on the road as well. According to the link I need 3 things to calculate VE and they are:

Intake Air Temperature

Mass Air Flow Rate in lb/min

Engine Speed

Because VE changes greatly on the 1.8T based on boost pressure, etc. I choose information that fit the following 3 critera as close as I could to 3k,4K,5k,6K and 7K RPM respectively.

My first task was to convert my g/s readings into g/min then to lb/min.

Given 6880 (my 7K value) I got 202.64 g/s (I know it should be higher, but were at almost 6,000 ft elevation here)and multiplied it by 60 to get g/min

202.64 x 60 = 12158.4 g/min

using that number, I went to an online mass flow calculator and divided that number by 0.002204624, which is the conversion rate.

12158.4 x 0.002204624 = 26.8047 lbs/min @6680 rpm

I caculated that amount for all the above listed RPM values.

The next step was to convert temperature to degrees Rankine. Of course the VAG COM only calculates IAT's in Celcius so I got those figures multiplied them by 1.8 and added 32 for defrees Feirenheit. Then added 459.67 to get degrees Rankine. So for 6880 rpm my IAT was

60C x 1.8 + 32 = 140F + 459.67 = 599.67R

Now it's time to calculate the air density of the 599.67R air entering the car to do that we will use the following formula, and solve for d2 which is the air density of the air entering the car..

t1/t2 = d2/d1

t1 = Temperature of air for a known density (32F @ 0.0808 lb/ft3)
t2 = Temperature of the intake air measured by the intake air temperature sensor (R)
d1 = Density of air for a known temperature (0.0808 lb/ft3 @ 32F)
d2 = Density of the intake air (lb/ft3)

459.67 + 32F/459 + 140F = d2/0.0808

d2=0.8199 x 0.0808

d2= 0.0662 lb/ft3

now that we have that figure we can move along to dividing the MAF in lb/min by the air density d2

26.8047/ 0.0662 = 404.9048 lbs/min3@ 6880 RPM

Before we go and calculate theorical air flow we need to convert our little 1.8L of displacement to in3. you can use a forumla or look in the model guide here on AW where it is already done.

107 in3, btw acording to the AW model guide.

Using that number we can now calculate theoretical air flow at our given RPM of 6880.

TAF = (ed)x(rpm)x(ve) / (es)x(c)

when
rpm = engine rpm
TAF = Theoretical air flow (ft3/minute)
VE = Volumetric efficiency (100% theoretical)
ED = Engine displacement (in3)
ES = Engine stroke (2 for a four stroke engine)
C = Conversion factor from in3 to ft3

TAF = 107 x 6880 x 1.00/2 x 1728

TAF= 736160 / 3456 = 213.0092

Finally to get Theoretical VE we need to calculate MAF/TAF

so 404.9048/213.0092 = 1.900879

VE = 1.900879 x 100 = 190.0879%

Now I know you are all thinking how can it be over 100%? That's the boost, that isn't present in NA cars.

Here is a nice spread sheet showing the TVE at a given RPM under WOT.

here are the final values, and they are represenative of my car only at that given altitude. If you have about 2~3 hours you can follow along in the link and calculate your own values and see how they vary from mine.

190.08% @ 6880
190.66% @ 6160
225.46% @ 4950
200.44% @ 3920
140.02% @ 3130

<img src="http://pictureposter.audiworld.com/48848/tve_under_load.jpg">

Tony@EPL

based off rpm/throttle angle with similar data.

Your data and the ecu data is offset a bit due to your increased air flow.

Nice work on the caculation!

Shep 1.8T

thanks..