Vems Map + Injector Sizing

[Bram]

I found http://www.efiexpress.com/catalog/ar...?articles_id=1

Damn fine webpage so yes injectors is just a calculation very good came up with a theoretical

750 cc injectors rated at 3 bar running at 4 bar = 866.03 cc / min
Therefore Stroker req+fuel = 6.49 * ( 2521.69 / 5 / 866.03 ) = 3.78 * .75 = 2.84

I'm having a play and seeing what I can learn before deciding what to do with the ecu, does seem though there is a lot to learn

In your calculation you should use the @3bar ccm number. not @4 bar. Or it must be that a UrS4 runs an FPR of 3 bar???? I thought it was 4 bar

At least this is what is stated in Marc's instruction:

As a guideline, set req_fuel according to the following calculation: req_fuel = 6.49 * (D / N / I) where D= engine displacement (ccs), N = number of fuel injectors, and I = injector flow rate (cc/min). To allow for finer grain fuel control I usually use 75% of this calculated number. So for an urS4 with stock injectors (280 cc/min @3 bar), req_fuel = 6.49 * (2200 / 5 / 280) = 10.2 * .75 = 7.65

[Jamo]

In your calculation you should use the @3bar ccm number. not @4 bar. Or it must be that a UrS4 runs an FPR of 3 bar???? I thought it was 4 bar

At least this is what is stated in Marc's instruction:

As a guideline, set req_fuel according to the following calculation: req_fuel = 6.49 * (D / N / I) where D= engine displacement (ccs), N = number of fuel injectors, and I = injector flow rate (cc/min). To allow for finer grain fuel control I usually use 75% of this calculated number. So for an urS4 with stock injectors (280 cc/min @3 bar), req_fuel = 6.49 * (2200 / 5 / 280) = 10.2 * .75 = 7.65

The injectors are rated at 3 bar the ABY runs at 4 bar so convert injector rating from 3 to 4 bar = 866 cc

The example is just an example, on his example map from the download link Req Fuel is set to 6

280 @ 3 bar = 323.32 @ 4 bar

6.49 * ( 2226 (the official engine size ) ) / 5 / 323.32 * 0.75 = 6.7

So it's closer to the actual map value than 7.65

[Bram]

OK I think I understand, then Marc did not do it very punctual in his calculation example as he should have used 4 bar injector flow rate and use the correct displacement. I think your assumptions are correct.

So for my engine spec it should be:

630 @ 3 bar = 840 @ 4 bar

6.49 * ( 2226 / 5 / 840 ) * 0.75 = 2.58

[GazzaG60]

sounds correct. i dont quite work mine like that. that gives a lower ms figure than the way i used.

what i will do is mod the map to reflect those figures. that should tell me if marcs way of req_fuel is better.

[Jamo]

OK I think I understand, then Marc did not do it very punctual in his calculation example as he should have used 4 bar injector flow rate and use the correct displacement. I think your assumptions are correct.

So for my engine spec it should be:

630 @ 3 bar = 840 @ 4 bar

6.49 * ( 2226 / 5 / 840 ) * 0.75 = 2.58

630 @ 3 bar = 727 @ 4 bar!

[GazzaG60]

how did you work that out jamo

[Jamo]

Square root of new pressure / old pressure multiplied by old pressure...........

Or just use the RC calculator http://www.rceng.com/technical.aspx

1 bar = 14.5 psi therefore 4 bar = 58 psi

[Rocco]

and the oem RS2 injectors rated to 4bar,for how many horse power at the crack will be valid??? 380hp??

[GazzaG60]

good spot that jamo.

i used to use an old calc like that but the calculator is much easier.

[Bram]

Square root of new pressure / old pressure multiplied by old pressure...........

Or just use the RC calculator http://www.rceng.com/technical.aspx

1 bar = 14.5 psi therefore 4 bar = 58 psi

I am learning everyday! Great that you pointed this out!

[Bram]

So again my setup

For my engine spec it should be:

630 @ 3 bar = 727.5 @ 4 bar

6.49 * ( 2226 / 5 / 727 ) * 0.75 = 2.98

[Bram]

and the oem RS2 injectors rated to 4bar,for how many horse power at the crack will be valid??? 380hp??

370-380 max @ 3.8 bar FPR

[Jamo]

and the oem RS2 injectors rated to 4bar,for how many horse power at the crack will be valid??? 380hp??

RS2 injectors

360 cc @ 3 bar
405 cc @ 3.8 bar <- FPR of the RS2
416 cc @ 4 bar

They will support 400 bhp, Mihnea has quoted as such IIRC on the forum

Anyhow back to VEMS there are injector threads covering this

[repo]

deka 006 flow chart:

http://www.kolumbus.fi/etelanlampo/siemens.jpg

Your calculation was suprizingly close.

e: injector CC/min = hp in our precious I5 engines.

[Bram]

deka 006 flow chart:

http://www.kolumbus.fi/etelanlampo/siemens.jpg

Your calculation was suprizingly close.

e: injector CC/min = hp in our precious I5 engines.

@ 3 bar I presume?

So Siemens Deka 006 630ccm@3bar injectors in our cars (using a 4 bar FPR) should be good enough for around 630 crank HP. I think Paul mentioned this before as well in another thread.