mg/R conversion factors?

Okay - call me lazy today - but really it is just time (lack of it)

Has anyone worked out the mg/Rev conversion to Liters/km or miles/gallon?

Anyone have the average specific density in g/l of diesel fuel?

thanks! (yeah I made a cable and have been checking the data - coool coooool numbers coming up)

I don't think you can do such a general conversion since the R/mi varies with what gear you're in. So you really need to figure it out for each gear.

Glad to hear the cable is still working.

Even if you figure out the conversion factor per gear, it only gives a ballpark figure, since the mg/R is not a measured quantity but a theoretical quantity. This explains why many people have noted that the MFA does not always match actual consumption.

Thus if you install "fat" injectors, your mg/R will decrease although your real consumption will remain similar.

But you factor in a couple data points from the display:

RPM

and indicated speed (computer display not Speedo).

Roughly will give you an idea, I'm not looking to be extremely precise - just close.

Okay foung a couple things I needed

Average specific density in Fuel is: 0.850g/l

so - well, my first quick run from trying to calculate consumption at 2625rpm, 14.8mg/r, 117km/hr, yielded some weird number that well it is too early this morning.

can I humbly ask anyone that has done this calc to share it with me? thanks

OK, I'll give this a try:

14.8 g/rev * 2625 rev/min * 1 g/1000 mg * 60 min/hr = 2331 g/hr

Now, I think your specific gravity is wrong. It's probably 850 g/L. So:

2331 g/hr * 1 L/850 g * 1 hr/117 km * 1 km/ .6mile * 1 gal/3.8 L = 0.0104544 gal/mile

or: 95 miles/gallon.

Now, here's where we need to look at the g/rev number. Does that mean the TOTAL number of grams injected into all cylinders during one revolution? or is it number of grams per cylinder-revolution? 2 cylinders fire per revolution of the motor... so if the number is per cylinder, that would mean that twice as much fuel would be used TOTAL per revolution of the motor... and that would make the above calculation:

47.5 miles/gallon.

that makes sense for cruise at 117 km/hr. does anyone know if the above logic is true? what is the true meaning of the g/rev reading in the measuring blocks?

-davin

It should be:

2625R/min x 14.8mg/R x 60min/hr x 1hr/117km x 1l/850mg = 23.4 l/km

Man what a fuel guzzler that would be!!

davin,

I must have gotten the specific gravity wrong that looks better and sounds about right.

the 47.5 number,


What I found was a variation between 12.0 mg/R and 17.8 mg/R at 117km/hr (73.125mph).

which would mean a range between 60 and 40 mpg at that speed setting with the cruise on.

on a roughly flat (compared to some states) with a little bit of wind.

Davin,
thanks alot for the info - now I can do the logs and the rough conversion - I would think this method would be close enough within a couple miles per gallon, No?!

I've got the numbers for cruise control set at 98km/hr

10-15.8mg/R
2205rev/min

gotta do another bio 101P tour! (oh joy)

What's the longest you can run a Vag-com plot, and can you integrate the result it produces?

If you could do even half a tank of fuel you'd get a good idea of how close it is - but remember that even filling the tank is really +/- 1/2 gallon and thus about +/- 5%...

Ted,

Vag-com seems to shut down/loose connection with teh ECU after about an hour.

Certainly not enough time. BUT I drive the same route pretty much all the time and well between Mt. Pleasant and Lansing there are 3 sections. 1st section 70mph speed - cruise set at 73 (according to vag-com) instant mpg around 47.5 - zone 2 cruise set at 61 instant mpg at 62.96 - then zone 3 same as the first one. Each one is about 20 miles or so long + the trip getting to and from the highway.

I'll see how long I can get a data log and get an integrated value for fuel consumption . . . in each of the three zones.

When I calculate the range in the slower zone the mpg is between 71.78 and 45.43!

(5 sp Golf GL stock MXV4 tires)

Hey GeWilli, what kind of sample rate are you getting? (it should say at the top of the screen)

I only get about 2.0 when measuring one block (and i think Davin gets the same, right?) but Uwe says most people get 3-4. I'm wondering if the problem is with the optoisolators on my board or if it's just that TDI controllers have a slower interface.

You guys should open up the log in Excel or something and try comparing the calculated numbers to what vagcom gives for fuel consumption in litres/hour.

I tried once but was off by about a factor of 2.1, which led me to thinking the same thing Davin said. I might try it again tonight... I've been playing with the VagCom this morning on the way to work to see how much of a difference the EGR makes in heating the engine up.

EDIT: Actually, have you even seen the block for fuel consuption in litres/hour? It's in measurement block 15.

[ October 15, 2001: Message edited by: Vroom ]

well when I run a single log rate I get 0.6 or so: well here are the 'numbers':
Group 001:
0.48
1.56
2.72
3.83
4.93
6.04
7.13
8.23
9.33
10.42

And Group 010:
1.02
2.17
3.29
4.38
5.48
6.58
7.66
8.78
9.88
11.04

not quite sync'ed up but it works.

When there is just one the sample rate is much faster.

I have been getting quite a bit of fast sync errors with this cable and the computer.

I don't know which end is messing up but as long as I don't get too greedy with the information it all works good -

made a nice graph this morning of a moderate accel run last night - using data blocks 001 and 010. . . .

I'm using the Jeff Noxom design board.
with a 150k resistor instead of the 140k specified. I don't know if changing the resistor to 200 or 140 (from 150) will fix my fast sync issue - but an instance last night came up where someone needed me to check their car out and well - the thing worked perfectly - I am addicted now.

Thought I knew about what was going on before? well watch out everyone cause here I come! i've got me somthing that is distracting me from my studies on wear rates fatigue factors and anti-wear chemistry and interactions with soot in oil . . . .

Me too.

Hi dieselists.

Sorry for necroposting in advance.
There's quite easy conversion mg/R to L/h and L/100km

For example numbers that posted above

I've got the numbers for cruise control set at 98km/hr

10-15.8mg/R
2205rev/min

Click to expand...

[ (12.9mg/R /0.86)*(2205/60/2)*4*3600 ]/1000 = 3969ml/hour

3,969/0,98 = 4,05 l/100km = 58mpg

0.86 density of summer diesel fuel
2 revs of crankshaft per one full combustion cycle (=one injection)
4 cylinders