NefMoto

We are all aware of the equation to calculate KRKTE, however, it becomes cumbersome having to use it all the time.
Something I have found to help me out a lot is make a KRKTE cheat sheet with data I obtained from multiplying KRKTE by the stock injector size.
For example: Stock AWP injector size is 317cc and stock KRKTE is 0.10311
So you take 0.10311 * 317cc = 32.68587  <--- That's your cheat number.
Now if you want to use the newer Bosch 415cc then you take 32.68587 / 415cc = 0.0787612 <-- That's your new KRKTE.
Now go for a spin and drive for a long time. After you are done you will get your long term fuel trim. Its a % number so multiply that % * your KRKTE and add or substract based on your fuel trim and go for a spin again. You should have your long term fuel trim pretty much right on the dot after 2 or 3 revisions.

Now the cool thing is that you can use this cheat number with any decent Bosch injector and it will always get you close enough.

If you use the regular formula/equation, you will still get pretty much the same number, but using this method saves time.
Eg.:
415cc/min x 0.684= 283.86
50.2624*(1.781/4)/283.86 = 0.0788393348833932

vs

32.68587 / 415cc = 0.078761133

I know most of the advanced guys know of this already but it should help a lot of people starting out.

Hmm, my stock injectors are 292cc's and stock KRKTE is also 0.103xx.

Are those 317cc @ 4bar?

I need to double check the partnumber on my stockers, I calculated my KRKTE the way you described and got 0.030xxx. If I use the FR formula I get 0.028xxx, but if my injectors are infact 317cc@3bar that would equal a KRKTE of 0.033xx using this method, huge difference  :)

Nope. 317 @ 3bar.
What year/model is your car?

02' A4 AVJ

http://www.usrallyteam.com/content/tech/18t_injectors.html

You got 205cc @ 4bar according to that page. I used this method to tune for Audi TT injectors on a Audi B6 1.8T and it got me within 9% LTFT right off the bat, but the B6 uses different injectors as well.

BTW when you start changing fuel rail pressure, KRKTE seems to get harder to calculate.

That is because pressure and flow are related through a square root curve, rather than linear as well as injector offset is dependent on pressure.

Bingo!

Using this method in this thread when changing fuel rail pressures will not work properly. The injector offset changes dramatically as you increase fuel rail pressure and this method does not compensate for it.

205cc@4bar lol, if I only knew.. haha

But this makes things even more wierd, why is my stock KRKTE 0.10356 if the injectors are infact 178cc@3bar?

178 x 0.10356 = 18.43368

18.43368 / 980 = 0.01881

This is really wierd, and why is it done like this? My injectors cant be as small as that, im going to check the partnumber to verify.

Here is a link to the binary I use: http://nefariousmotorsports.com/forum/index.php?topic=1103.0 (http://nefariousmotorsports.com/forum/index.php?topic=1103.0)

found my error, my KRKTE factor is wrong at 0.000111.

If I put in 0.000167, ~everything lines up at 205cc@4bar.

BUT, according to that site, both the "282cc" injectors used in US spec cars have the same PN as my Euro spec 205cc injectors. And the KRKTE is the same 03A5 from my Euro binary and the US binarys.

Ninja edit #10: Gonzo, they are 205cc@3bar not 4bar.

Something is fishy about those CC numbers on that site, doing the math backwards from my flowtested injectors @980cc using my real world KRKTE would put the stock injectors at ~308cc's.

But thats really rough as my wall wetting is still stock and my injectors are not likely 100% linear at partial throttle.

I used 282cc for the Audi B6 1.8T (with the returnless fuel system) with this method and then used 386cc for the new injectors (since they were TT injectors) and this got me super close (within 9% like I stated before). Check to see what injectors you really have. Maybe I'll take a look at your BIN and compare to the North American spec one.

I agree. The stock numbers are out of whack given the typical KRKTE values I use for other injectors.

Even given that, I cannot square my KRKTE values with the stock injector flow rate here:

http://s4wiki.com/wiki/Fuel_injectors

I have been saying forever that I am pretty sure we are all wrong about stock injectors specs.

I think they are 319 and not the commonly thought 349

b6 a4 is a static fuel pressure, may have something to do with why krkte is the way it is? 

fuel pressure inceases/decreases should NOT be handled in krkte when using pretty much anything much bigger than stock injectors, i use tvub to deal with fuel pressure increases

Stock injector PN

Alright, just for fun, 282 x 1.09 = 307.38cc

Scary close to what I calculated also ;)

Yeah its good trick to start with  :)

Wow I didn't think of that haha.

So where did the 1.09 come from?

The 9% Gonzo mentioned he had to sub to the KRKTE to get the trim down to 0, using this type of fast calculation(im assuming he subtracted, based on partial fuel trim being -9%).

Trim was actually +9

correct me if im wrong, but shouldnt the KVB value pretty much reflect the STOCK injector size in cm3/min, if you are uncertain of the stock injectors size..

Yes!!

Please tell me more about that

It's the fuel consumption constant.

Used to calculate MPG/miles to empty, etc on MFA clusters.

Ahh, thats one of the million things I need to address.

My cluster says 1800km until empty when I refill lol

Why, with the same injector part number (06A 906 031 BC - bosch 0 280 156 064) and fuel pressure regulator, the ECU for S3 1.8 turbo 210ps (AMK) and 225ps(BAM) have different KRKTE?

AMK has 0,08347
BAM has 0,08358

thank you

This is helping me a lot, but I was wondering if this value is influenced by how much bar the fpr is pushing, or not at all? I ask because my passat uses a 4 bar fpr, and my KVB value is 234.61, which looks pretty low.
I looked at a BAM TT 225 KVB value and it was 371.72, which seems right since that car is running 386cc injectors @ 3 bar.

I have a set of genesis 380cc injectors that are going in, and I want to make sure that KRKTE is as close as I can get from the start.

Thanks!

Sorted  :)

is there a way to work this equation backwards to find stock injector size via krkte?

According to the FR and snook, stock KVB reflects injector size in cc/min. That would mean the S4 injectors are only 30# vice 33#.

thank you sir. at some point in time i read this whole thread. must have forgotten i read that part.

bump to find easier