Fuel load under deceleration

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BlackBird_SR71
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Fuel load under deceleration

Post by BlackBird_SR71 »

I'm tuneing a Turbo car and currently have the AFR Table Fuel load calculated from 40kpa to 250kpa. Question is, what happens under declaration when fuel load goes into negative values such as -70kpa. Does the fueling stay at the same values as last seen on the table. As it's only a 12 x 12 table, I've tried to scale it accordingly.

Same question with ignition table and fuel load.

Here's the table in question. Note Baseline tune only. Car is running at low boost ( 7 psi ) and final tuning yet to be done:
AFR005.jpg
ol boy
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Re: Fuel load under deceleration

Post by ol boy »

No such thing as negative kpa. Deceleration values should be around 20ish kpa.

The math will pull from the last value in the colume. Everything below 40kpa at 3k rpm will uses 14.7.

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BlackBird_SR71
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

ol boy wrote:No such thing as negative kpa. Deceleration values should be around 20ish kpa.

The math will pull from the last value in the colume. Everything below 40kpa at 3k rpm will uses 14.7.

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Thanks, that is what I want'ed to know. Actually deceleration values can go into negative Kpa. It is not uncommon for engines to pull 20 to 25 in/hg on decell. That's approx -70Kpa to -80Kpa. MS 12 x 12 table just doesn't have the resolution for that. Not that it really matters though...
Kpa005.jpg
My Haltech which has 32 x 32 Tables and lists Kpa load from -100Kpa to 600 Kpa in it's default Map. Of course I'd rescale to fit application. ( Picture below is only 85% . Couldn't fit whole table on screen, but it goes to 600Kpa... which is a bit much )
Kpat0010.jpg
ol boy
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Re: Fuel load under deceleration

Post by ol boy »

The MAP sensor is an absolute pressure sensor not a gauge type. So it measures from 15ish Kpa to 250ish Kpa. 0.2ish volts to 4.8ish volts is the output range covering the pressure range.

The calculators you are quoting are assuming zero Kpa being the pressure seen on a gauge referenced to sea leave. So doing the math with everyone starting at sea level you will then get negative numbers.

But.. we use absolute pressure. At 0 Kpa you're on the moon. I assume digging a 3000 foot hole on the moon won't get you into negative Kpa values either.

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BlackBird_SR71
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

Since the table pulls from lat value if load goes off table, I can rescale AFR Load Axis for more resolution with high boost. That's why I rescaled from 40 to 250 Kpa. Does that scaling look adequate? TIA.
BlackBird_SR71
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

ol boy wrote:The MAP sensor is an absolute pressure sensor not a gauge type. So it measures from 15ish Kpa to 250ish Kpa. 0.2ish volts to 4.8ish volts is the output range covering the pressure range.

The calculators you are quoting are assuming zero Kpa being the pressure seen on a gauge referenced to sea leave. So doing the math with everyone starting at sea level you will then get negative numbers.

But.. we use absolute pressure. At 0 Kpa you're on the moon. I assume digging a 3000 foot hole on the moon won't get you into negative Kpa values either.

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Ah thank you. I get it now. It looks like Tuner Studio does it one way and HalWin the same as the online calculators. You can clearly see that Halwin does use negative Kpa load values. Is that a correct conclusion?

In the TS I entered 250Kpa as maximum boost level in the table. That should be equal to about 21 psi of boost. Does that look correct?
ol boy
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Re: Fuel load under deceleration

Post by ol boy »

Yep.

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BlackBird_SR71
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

Delete... mucho confusion
Last edited by BlackBird_SR71 on Wed Apr 19, 2017 10:19 am, edited 1 time in total.
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

Anyhoo.. thanks for answering the basic question. All I needed to know is that last readings were retained if actual Kpa figures went
ol boy
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Re: Fuel load under deceleration

Post by ol boy »

14.5psi of what? In engine world.. 14.5 psi of boost is 200kpa.. we start at 0 psi which is 100ish kpa.. that's why a 2.5 bar (250kpa) sensor is good to 21 psi.. (2.5 x 14.5) - 14.5 is 21.7ish psi.

Back to your first examples.. 20inhg being -70 kpa.. 100-70 is 30.. at 30kpa MAP you should show an 20 inhg of vacuum on a gauge. I pull these numbers from my head they maybe off but the theory is there.

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BlackBird_SR71
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

Thanks. Edited and deleted my Post above. Had a hard time wrapping my head around Absolute Pressure, Gauge Pressure, Kpa, Psi and inches of HG. I think I've got it now. Difficult when two different pressure absolutes are used between programs ( TS and HalWin )
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Re: Fuel load under deceleration

Post by whittlebeast »

Got to go with ol-boy on this one. In the real "engineering world" there is no such thing as negative pressure. Outer space say a million or so miles above earth, the pressure is by definition, real close to 0 pressure absolute. You may find a gas molecule around somewhere if you look real hard.

What you are looking at in that screen shot is a set of pressure units that has that has been shifted and re scaled to read 0 at 100 KPA absolute pressure.

Andy
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

whittlebeast wrote:Got to go with ol-boy on this one. In the real "engineering world" there is no such thing as negative pressure. Outer space say a million or so miles above earth, the pressure is by definition, real close to 0 pressure absolute. You may find a gas molecule around somewhere if you look real hard.

What you are looking at in that screen shot is a set of pressure units that has that has been shifted and re scaled to read 0 at 100 KPA absolute pressure.

Andy
Default Map with no changes from HalTech software. Not re-scaled. So how would I interpret that? Note: Oldish HalWin software. E11-1 on HalWin 1.71. That's the scaling in all the Halwin E8/E11 tables around the mid 2000's. Realise this is a MS forum... so if breaking any rules, please ignore question.

Got my answer for Ms and how Tuner Studio does it so that was my main quesion. But now the HalWin table is really confusing me ( Ignition table uses same default scalling on 32 x 32 table )

Edit: Think I have it figured out. Thanks Ol Boy and Andy. The old Halwin tables actually use the -XX figure as the minus figure from 100Kpa so -70 on the Halwin table is: 100 -70= 30kpa. Only they don't show the 30kpa figure, they show the subtracted value from 100 Kpa. Does that sound correct?

Here's a screenshot of 2D Map. Full Load is shown as 0 ( Far right ) and then boost starts at 4
ScreenShot001.jpg
Last edited by BlackBird_SR71 on Wed Apr 19, 2017 2:53 pm, edited 2 times in total.
ol boy
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Re: Fuel load under deceleration

Post by ol boy »

I'd think a data log would tell you a lot about how they are doing the math.

Like Andy said"
What you are looking at in that screen shot is a set of pressure units that has that has been shifted and re scaled to read 0 at 100 KPA absolute pressure."

So -70 kpa is really 30kpa and -30kpa would be 70kpa. If you can convert the haltec data log into an excel or csv you could add a column and do some math to change it to absolute MAP.

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BlackBird_SR71
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Re: Fuel load under deceleration

Post by BlackBird_SR71 »

ol boy wrote:I'd think a data log would tell you a lot about how they are doing the math.

Like Andy said"
What you are looking at in that screen shot is a set of pressure units that has that has been shifted and re scaled to read 0 at 100 KPA absolute pressure."

So -70 kpa is really 30kpa and -30kpa would be 70kpa. If you can convert the haltec data log into an excel or csv you could add a column and do some math to change it to absolute MAP.

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Gotcha was typing at same time as you and came to same conclusion. Thanks.

Wacky way to do it, but it is old software. Have just bench tested unit and tried a trial startup. No data logs yet. Been tuning a few MS2's lately and more used to their software. HalWin was confusing me...
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Re: Fuel load under deceleration

Post by rickb794 »

I don't think you need to worry about decell in the VE table. There is a fuel cut feature that takes care of that.

See "Over Run Fuel Cut" under the "fuel settings" tab

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