NefMoto

Ok... so I've been doing some reading, and calculating, and more reading and more calculating and I've come to the realization I don't know jack shit, because what I thought I knew doesn't add up (literally).

Let me explain.

My car drive's OK with a KRKTE @ 0.048 LTFT's are around 3-4%... it's where I was told a while ago that is what my KRKTE should be with my injectors (1000cc @ 3 BAR, running stock 4 BAR they're approx 1168cc or so).

Fine..

Stock S4 injectors are 33#/hr or 349cc/min... great.... M-box KRKTE is 0.147... right... moving along...

to Caluclate KRKTE according to the PDF:

KRKTE = 50.2624 * Vhzyl / Qstat

Vhzyl = 0.450

Qstat is the flow rate of your injectors using n-Hep in g/min.  No idea at what pressure though... 3 bar, 4 bar, 10 bar no clue.

Right so, stock injectors @ 4 bar are 349cc let's add 5% for n-Hep and then convert to g/min... so we a Qstat for the stock injectors @ 3 BAR = ~217 g/min  at 4 BAR ~239g/min

Plug that into our known equation above from the PDF and we get something completely different from the M-box value.

@ 3BAR, KRKTE = 0.10423
@ 4BAR, KRKTE = 0.09463

My injectors @ 4BAR the KRKTE would be approx. 0.02692

What gives, and what am I missing here?

There is something funky with that PDF, but lets ignore that for the moment.

I believe the stock injectors are 349cc/min (249g/min) at 4 bar (not 3 bar)

Still.

50.2624 * .450 / 249 = .0908, which is quite far from stock.

 

Just a very quick thought as I'm off to bed but it's probably an issue with the units of measurement. A quick look at the DAMOS shows that the unit of KRKTE is milliseconds/% Load (I presume) so the figure of around 0.1 looks correct because it gives an injector on time of ca. 20 milliseconds at full load with the example Qstat values you supplied.

Also remember that the PDF we all know and love is for the 132 kW 1.8T 20 valve project, not your 2.7 twin turbo S4.

Doug

What units is 50.2624?

If we had that, I think we can fill in the rest to get it to msec/% by just doing unit analysis.

Ok. Lets try this again.

100% load is 0.4452 liters of air at standard density

That's 0.5455 grams.

At 14.7 AFR, thats .0371 grams of fuel

For an injector spraying 249 g/minute, thats 8.94ms for 100%, or 0.0894ms/%

EDIT: my half cycle thing is junk.

It should be 0.0894ms/% or 0.0897ms/% assuming reference air density of 1.2293

(1.2293 kg/m^3 * .4452 liters / 14.7) / 249 g/minute / 100 in ms = (http://www.google.com/search?q=(1.2293+kg%2Fm^3+*+.4452+liters+%2F+14.7)+%2F+249+g%2Fminute+%2F+100+in+ms%3D)

with 1.05 correction, thats still 0.0934

Sigh.

I can shed very little more light on it except that when I plug in the numbers quoted in the funktionsrahmen, I get 47.813 instead of 50.264. This figure is just the air density in g/dm^3 divided by the product of a bunch of constants, i.e. 1.23 g/dm^3 100 x 14.7 x 1.6666E-5 x 1.05.

The only other thing I could think of is that the air density is quoted at 0 degC/32 degF if the funktionsrahmen is to be believed. This is a bit odd since most values are taken at STP, which is 25 degC if I remember high school physics/chemistry correctly. If KRKTE is internally corrected by the ECU or externally corrected by a tuner, this could explain a difference, but that would tend to lower KRKTE a little bit, not increase it.

I just looked at a DAMOS for the S4 2.7T and KRKTE is 0.09778 ms/%Load, so I'm not sure where you're getting 0.147 from.

Doug

on any stock 2.7t s4 file the krkte is set to 0.147

Maybe we've been starting with the wrong stock injector size all along?

Perhaps 33lb @ 4 bar is wrong?

Ok. Lets take a different approach.

The Audi P/N for the grey tops is 078 133 551 M
Google says the corresponding Bosch P/N is 0280150921

Now, I get a bunch of different flow results for 0280150921 on google.

this (http://clubgti.co.uk/forum/showpost.php?s=78e62f3edace95cc61e3ec40ecaf2599&p=1882108&postcount=4) says 156cc/min @ 3bar, or 208cc/min @ 4 bar

(http://www.witchhunter.com/flowdatapix/b0280150921.jpg) suggests 168cc/min @ 3 bar, or 224 cc/min @ 4 bar

There is something very fishy going on.

No, it's 0.09768 as Doug wrote, checked G and M-box.

I checked an RS4 2.7T DAMOS and KRKTE is 0.06756, so that's quite a bit lower. The spec. said 380 bhp for that file so some evidence there that the higher power tunes have lower KRKTE and injectors with larger Qstats will obviously reduce KRKTE, as we know.


A Qstat of 223 g/min corresponds to the funktionshrahmen constants, a Vhcyl of 0.4552 litre and a KRKTE value of about 0.0976 so that all ties up. I checked Elsawin and the AGB & AZB engines do indeed have a 4 bar FPR. Checking up on the spreadsheet from www.mksautobusiness.fi gives the following injectors designed to operate at 4 bar and 223 g/min (Bosch part numbers):

0280155899
0280156052
0280157004
0280157005

The other issue to be aware of is to make sure we're not confusing g/min with cm^3/min because with the density of gasoline being about 0.75 g/cm^3, that will make a significant difference to a calculation.

Doug

Interesting... I just checked the A6 R box and it is 0.09783 as well.

Checked S4 2.7T H-box: 0.17216

Weird. This is what I have in my bins

4Z7907551R 0.09783
8D0907551F 0.06756 (RS4)
8D0907551G 0.09778
8D0907551M 0.14696 !!!

unless I have a non-stock mbox bin floating around.

I just discovered the problem. When I did my XDF, I primarily used the a6 R-box as a reference, which uses factor 0.000167 for KRKTE

However, F and G both use .000111

I'm so sorry guys, this is all my fault. My XDF is WRONG!

Here's the deal:


Notice M and G are the same :(

ETA:

Fix available here (version 20110825)

http://nefariousmotorsports.com/forum/index.php/topic,200.msg8108.html#msg8108

ah, now it makes so much more sense.
good catch

Excellent discussion clearing up a few myths. Thanks for some great challenges guys.

Doug

It's all good! :)

In either case remember to update your M-box XDF posted on here (I'm sure you already have).

Great, so I'm glad that's solved... I was really scratching my head on that one for a while lol

yeah, no worries.  fixed my definition thanks. 
I love this forum.

20110825 release here

http://nefariousmotorsports.com/forum/index.php/topic,200.msg8108.html#msg8108

so have we decided what the true stock injector flow rate is?

349cc @ 4 BAR seems to be correct or at least very close... but you cannot be certain working backwards from the bin.

I think they might be 319cc as if you do the math that meshes with the stock krkte value.  349cc = .09337

I got 320 cc/min from KRKTE of 0.09778 and the funktionsrahmen expression so I thought I'd have a look at ELSAwin to get the actual figure but all I could find was a wide range of 270 to 330 cc/min. This is also a PITA because the test medium is gasoline from the fuel tank. So we would then have to correct this figure by the ratio of the density of n-heptane (0.6795 g/cc) to the gasoline in use. However, If we just use the 'petrol factor' of 1.05 in the funktionsrahmen which would result from a gasoline density of 0.7135 g/cc, (although I understand premium is nearer 0.75) this would give a Qstat range of 283.5 to 346.5 cc/min (n-heptane).

Not as helpful a conclusion as I had hoped :-(

Doug

So, that means across the globe we get fuel of varying density etc...so the calculations will vary a bit ...?

I've given up trying to find the right theoretical value for krkte and just tune it empirically

there you go.  I gave up on a "formula" a LOOONG time ago.  just never has worked for me. :(

I just do percent change, and then fine tune from there.  Usually its within 6-7% on the 4 sets of injectors i had calibrated.  Good enough starting point realistically.

hello guys,
I need your help.
I have a tt 225 with map and air filter
I would like to add a fuel pressure regulator from 3 bar (standard) to 4bar

I have not understand  if I need to change only KRKTE or I need to change  FRLFSDP too

thanks
Daniele

KRKTE is what you need to change.

thanks for your support
 ithink that 386cc @3bar whit new fuel pressur regolator @ 4bar became 445cc,  isn't it?

whit this calculator http://nefariousmotorsports.com/forum/index.php?;topic=4021.0  ( i' have tested it! it works fine whit oem value )
my new value is KRKTE   =   0,073223304

do you think i need to modify KVB for fuel consumption ?
thanks !!!!

Yes, if you want dashboard display to be somewhat accurate. Multiply KVB by %change in KRKTE.

TVUB should change, too, it will injector lag will increase with increase in pressure.

thanks a lot,
I probably need to look for a new flow converter.
from 3 @ 4 bar the expected decrease is 15% but I get only 12%.

if I confirm that my calculation is right i'll multiply by 12% KVB and TVUB

:)

i use this flow converter http://witchhunter.com/injectorcalc1.php
can you suggest another one?

Do not multiply TVUB by 12 percent.

this xls return the same result
 https://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CFAQFjAE&url=http%3A%2F%2Fwww.dtec.net.au%2FTech%2520Articles%2FInjector%2520Data%2520%26%2520Flow%2520Converter.xls&ei=SzFFUqf0HKP_4QTQjYGoDA&usg=AFQjCNHT8xUq_o_DYS8NOTpm_McJ_EndCA&bvm=bv.53217764,d.bGE&cad=rja

probabli 386 cc @3bar  are 455cc @ 4bar :)

thanks i'll study tvub increment better

in according with this post
http://nefariousmotorsports.com/forum/index.php?topic=320.msg18426;topicseen#msg18426
probably i must divide by 1.1852 tvub value :)

i must verify if this http://www.boschdealer.com/specsheets/0280158117cs.jpg is valid for tt 225 injector ( i think is it )

no i think is not corerct :(