B4001 Data Question (Whipple install on 2011 Camaro)

[cmkelly01]

I'm trying (without luck) to make sense of something. I have a 2011 Camaro with a Whipple supercharger. Whipple provides their own cal file which seems to work fairly well in actual use. I've been looking it over to see what they changed, and why, but I can't figure out B4001. The attached PDF shows the original stock tune on top, and the Whipple version on the bottom. The top curve makes sense to me, but the bottom one doesn't. There's no way this discontinuous curve matches the actual flow curve of the new injectors, and I was wondering if anyone knew why Whipple would use this sort of "curve"? There has to be a good reason, but it's beyond me. Any ideas?

[joecar]

The Whipple IFR table shows that the FPR is MAP-referenced.

Did the Whipple come with injectors...?

Stock setup uses unreferenced FPR, so the curve has a squareroot shape to it (i.e. it slopes with delta MAP).
When a MAP-referenced FPR is used, the pressure difference across an injector is constant, so the IFR is flat, the operating range being from 5-bar down to 4-bar (for unboosted) and down to 3-bar (for 1-bar boost) and down to 2-bar (for 2-bar boost)... the step is outside the operating range.

( can you repost the screenshot with units set to Metric...? Go Edit->Configure Display Units, click Metric, exit tunetool, reopen tunetool. )

[cmkelly01]

Yes, it came with injectors. The metric version of the screenshots is attached. Thanks for the explanation!

[joecar]

Yup... the range 400-480 kPa is for NA, the range 300-400 kPa is for 1-bar boost, the range 200-300 kPa is for 2-bar boost

( the step is at 548 kPa, outside the operating range ).

[cmkelly01]

Thanks! One last (hopefully) question: You said "The Whipple IFR table shows that the FPR is MAP-referenced." When I look at B1209 (Injector Correction MAP/Vac Selection), it's set to Vacuum in both tunes. How does the ECM know that it's now supposed to be MAF-referenced?

[joecar]

B1209 sets the axis for B4001 (and for the injector voltage correction table)... i.e. the axis can be vacuum or Delta MAP (i.e. two different ways to present the IFR table);

the difference between vacuum and Delta MAP:
- vacuum is simply BARO minus MAP (vacuum goes negative when in boost);
- Delta MAP is the pressure difference across an injector (i.e. top minus bottom);

the pressure on top of an injector is FPR pressure (i.e. rail pressure... or more correctly, absolute rail pressure);
the pressure on bottom of an injector is MAP (i.e. manifold absolute pressure);

absolute rail pressure can be either one of these (but not both):
- constant in the case of un-referenced FPR (e.g. constant 400 kPa psi plus BARO (to make it absolute));
- varying pressure in the case of MAP-referenced FPR (i.e. rail pressure varies with MAP)(e.g. 400 kPa + MAP + BARO).

The ECM does not use vacuum, it looks up and computes in terms of absolute pressure.

More info: Calculating-Injector-Flow-rate

[cmkelly01]

But when I change B1209 from "Vacuum" to "MAP" (or vice-versa), save and then reopen, the B4001 axis always says "Delta MAP". That's why I'm confused.

Also, if the B4001 "Delta MAP" values are increasing (from left to right), how can the injector output stay the same (straight line)? You said previously "When a MAP-referenced FPR is used, the pressure difference across an injector is constant, so the IFR is flat", which makes sense, but the "Delta MAP" axis values aren't constant - they increase from left to right.

[cmkelly01]

Joe, sorry to keep beating this dead horse, but I've looked around for answers, and I'm still confused. When I change B1209 from "Vacuum" to "MAP" (or vice-versa), save the file and then reopen, the B4001 X-axis doesn't change at all. The number range stays the same, and the title stays "Delta MAP". Shouldn't something change, at least the title?? I don't see any evidence that the calibration understands that the FRP pressure reference has changed from "constant value" to "MAP referenced.

[joecar]

I'll find out more about this...

[cmkelly01]

Thanks - I really appreciate your efforts. Sorry to be such a pain in the ass!