Intake Manifold Volume derived from what??

[Redline Motorsports]

In better understanding how the airmass is finalized to determine fuel mass the following logic is used;

The MASS AIR meter measures the grams/sec of air mass entering the intake manifold. This is a raw measurement. What the PCM really cares about is grams/cylinder NOT air mass. However in order to determine the exact grams/cylinder it needs to be "predicted" based upon certain assumptions.

This is where the VE coefficients come into play as well as intake manifold volume.

At steady state the MASS of air entering the MAF should "closely" compare to the grams/cyl entering the combustion chamber.

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The diagram above shows the air dynamics associated with a throttle movement. When the throttle (in blue) moves, there is a big rush of air through the throttle to fill the intake manifold. The air flowing into the manifold (as measured by the MAF sensor) is in red. The air flowing into the cylinders (in green) lags behind this because of the manifold filling effect. The area between the red and green curves is the amount of air that has added to the manifold.


At the beginning and end of the chart, the system is in steady state, which means that the amount of air in the manifold is constant. The air flowing through the MAF sensor is equal to the air flowing into the cylinders. Once you jab the throttle that all changes and the surge of airflow (transient condition) now requires that the speed density calculation assist in the prediction of grams/cylinder. Stuck in the middle of the this condition is the intake manifold that has a known volume as indicated in the {B8036} parameter for volume....

Now.....we install a LSX 102mm intake or better yet a positive displacement supercharger.....seeing how the 15 string polynomial calculations looks at this it seems like we really should be correcting for this when making these changes.

Question I'm trying to answer is the value that is noted in a give calibration is the raw manifold? or with the runner in the cylinder head....or.....with the neck of the throttle body.....etc.....



This also leads into the "Predicted Charge Temp Coolant Modifier" {B0179} and "Predicted Charge Temp Filter" {B0180} as these are also tables that derived as a dynamic of the intake manifolds design.....

It is necessary to know the mass of air trapped in the cylinder when the inlet valve closes. The amount of air trapped in the cylinder is used to calculate the amount of fuel to inject, spark timing, and the torque estimation. oh!!! Torque estimation......hmm....doesn't the 6L80/90E require torque values for shifting.........I'm exhausted for explaining that to people who keep destroying those trannys.......


It is known that a speed density calculation of fresh air mass matches the actual trapped fresh air mass when the speed density calculation is timed to occur at Bottom Dead Center (BDC) of the intake stroke. Because of the way the engine control module works, the calculation must occur at approximately Top Dead Center (TDC) of the intake stroke. This is to allow a fuel mass calculation based on the fresh air mass estimation to occur in time for the fuel to be injected before the intake valve closes.

There is a lot more to this topic but right now I'm homing in a the importance of this value.......

Howard

[nevinsb]

What do you use on tunes that don't have B8036? Just adjust the dynamic fueling?

[Redline Motorsports]

The point of the post is to understand the boundaries in which GM quantifies the values they use. I'm sure all of GMs calibrations have provisions for manifold volume just EFILIVE doesn't pull it out.

[joecar]

Hmmm, very interesting...

I don't know the details/existence of the intake manifold volume tables, but this is exactly why the VE/VVE tables are required to be correct.

[nevinsb]

So, this is directed at the newer PCMs.

[gmh308]

Now.....we install a LSX 102mm intake or better yet a positive displacement supercharger.....seeing how the 15 string polynomial calculations looks at this it seems like we really should be correcting for this when making these changes.



Very very good question. Typically they are around 9.5 to 10 litres for an LS3 intake and 11.3 for an LS7. Without getting an intake off the shelf and blocking the ports and filling it full of water (but now I am curious :)), I would guess it is the entire intake volume including ports, unless they are subject of a separate calibration number hiding in there. Its all the one body of elastic air that takes time to normalize on rapid throttle movements.

[Redline Motorsports]

Very very good question. Typically they are around 9.5 to 10 litres for an LS3 intake and 11.3 for an LS7. Without getting an intake off the shelf and blocking the ports and filling it full of water (but now I am curious :)), I would guess it is the entire intake volume including ports, unless they are subject of a separate calibration number hiding in there. Its all the one body of elastic air that takes time to normalize on rapid throttle movements.

We are going to cc one here shortly...I guess if a stock one equals "X" and the new one equals "Y"; then the delta between could just get added to the value noted IF that value doesn't match the measured....its about as close as you can get for taking a stab at it.

I am 1000% convinced that it plays a huge role after analyzing the coefficient formula and logic for Dynamic Airflow. I think that the E38/67 is so damn fast in calculating that it just absorbs so much error!

I blame a lot of transient issues on injector STOMP IMPACT FACTOR and WALL WETTER issues but I think a lot is solved in this topic..

HT

[gmh308]

There is also the VE Compensation tables which have an influence on transient conditions on a per VVE zone basis - but maybe you already have those under control :).

[Redline Motorsports]

There is also the VE Compensation tables which have an influence on transient conditions on a per VVE zone basis - but maybe you already have those under control :).

Yes but those table are what I would refer to as "trimming" tables vs. constants that are specific to the component...very much like an injector.

[swingtan]

Interesting reading.....

I've looked at Manifold Volume a bit in the past and tested the effects on the overall fueling of the motor. As already mentioned, it seems to effect dynamics, but mainly in MAF metered tunes. It's been fairly common knowledge that removing the MAF and running a SD tune tends to mess up the dynamics a lot, making the engine feel doughy on sharp throttle movements. For those running an auto trans, this hasn't really been a big issue, but on a manual car, the dynamics (and anything that impacts dynamics) make up a large portion of the tune. Think about what happens if the ECM is correcting for the manifold filling, but never sees that initial rush of airflow to fill the manifold. I'd say that the engine would go lean on throttle tip in.

The theory here is that setting a manifold volume to a larger number, would reduce the dynamics fueling, as the ECM thinks more of the airflow is being used to "fill" the manifold rather than the cylinders. Don't forget that the opposite is true as well, as the throttle closes, additional air will continue to fill the cylinders as the manifold vacuum rises.

As for how the volume is calculated, I'm going to hazard a guess that it's from the TB blade, to the back of the valve, IE. the actual manifold an the port volume. This seems logical as it allows the E38 to compensate for the total air volume.

Finally, other airflow calculations... Yes, these seem to be impacted and torque calculations can get pretty messed up. The E39 does everything via commanded torque vs estimated torque, so getting the derived torque figures wrong results in a pretty ordinary tune. I haven't seen any dynamics table in my E39 OS, and while you may not think any are needed in a direct injection engine, I feel there is still something there, at least in terms of charge temp blending ETC.

Great topic Howard, Happy New Year to all.

Simon.

[gmh308]

Yes but those table are what I would refer to as "trimming" tables.

Absolutely. :) Happy New Year to all!

[gmh308]

up cho bác, chúc bác nam m?i may m?n, chúc di?n dÃ*n ngÃ*y cÃ*ng pr cao!

Yes Happy New Year to you too! Phuc Mung Nam Moi yes? In February though. :)

[GMPX]

Yes Happy New Year to you too! Phuc Mung Nam Moi yes? In February though. :)
Are these guys even using a language or did he's cat walk across he's keyboard?
FYI, our spam filter would catch at least 15 of these exact same posts every day, some people live a very sorry life.

[gmh308]

Are these guys even using a language or did he's cat walk across he's keyboard?
FYI, our spam filter would catch at least 15 of these exact same posts every day, some people live a very sorry life.

Yes very sorry life. Oh to have that much time to be so bored to go to the effort of getting an ID on forums to post mumbo jumbo. Seriously though, it looks like Vietnamese. ID also.

[Redline Motorsports]

Here is a break down of how this is calculated and why running both MAF AND SD are fundamentally correct.

Since the MAF sensor cannot be used to calculate the base trapped fresh air mass per cylinder during transients, a different approach must be used. DYNA-Air uses the speed density approach, which uses the Ideal Gas Law to calculate cylinder air mass using the following equation.

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Where: mcyl = estimated trapped cylinder fresh air mass in milligrams, molar mass is the conversion from moles to milligrams for air, MAP is the pressure of the air in the manifold, Vcyl is the volume of the cylinder, R is the Ideal Gas Constant, and ChgTemp is the temperature of the air entering the cylinder, also called charge temperature.
The only items on the right side of this equation that are not constant are MAP and ChgTemp. MAP is measured by a sensor. ChgTemp is estimated by the engine control module.
Equation 2 cannot be successfully used as shown because the cylinder volume is not always fully filled with fresh air. This happens for several reasons:

The intake valve does not close exactly at BDC, which is when cylinder volume is the greatest.
ƒ Intake manifold tuning can change based on engine operating condition.
ƒ Not all of the exhaust gets expelled from the cylinder during the exhaust stroke, which will allow less fresh air to enter.


The solution to this issue is to construct a Volumetric Efficiency (VE) as a function of engine operating condition. This VE is defined as the percentage (from 0 – 100%) of the cylinder volume that gets filled with fresh air at a given engine operating point. Engine operating condition is defined by MAP, Engine Speed, and any other engine feature affecting VE (including IMTV position, DoD state, cam phaser position, etc).
The VE is incorporated into the speed density equation as follows.

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One issue with VE is that it varies with temperature, barometric pressure, and from vehicle to vehicle. Also, charge temperature parameter is not measured, and could be inaccurate. These are some of the reasons to actively correct the speed density calculation to account for differences between the engine used to calibrate the VE and the engine that is actually being operated.


The solution to this issue is to compare the speed density calculation to the MAF sensor when air dynamics are steady state. Based on this comparison, a correction factor for the speed density is calculated. This correction factor is then used during transients to account for the current condition of the engine.

The fundamental strategy of DYNA-Air is to use the MAF sensor during air-dynamic steady state, and use a “corrected” speed density calculation during air-dynamic transients. This correction called VECORR, and is calculated using the following equation when steady state conditions exist.

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VECORR is calculated only when the engine is in a steady state condition. VECORR is only used when the engine is in a transient condition.

[joecar]

I have a comment on this:




The solution to this issue is to compare the speed density calculation to the MAF sensor when air dynamics are steady state. Based on this comparison, a correction factor for the speed density is calculated. This correction factor is then used during transients to account for the current condition of the engine.

The fundamental strategy of DYNA-Air is to use the MAF sensor during air-dynamic steady state, and use a “corrected” speed density calculation during air-dynamic transients. This correction called VECORR, and is calculated using the following equation when steady state conditions exist.

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VECORR is calculated only when the engine is in a steady state condition. VECORR is only used when the engine is in a transient condition.VECORR is the difference between airmass due to MAF and airmass due to VE during steady state...

if VECORR is applied to MAF during transients, then how is this different that using VE during transients...?

( notice here that VECORR is calculated during steady state, and that VE is steady state VE, and that MAF is steady state MAF )

[Redline Motorsports]

I have a comment on this:

VECORR is the difference between airmass due to MAF and airmass due to VE during steady state...

if VECORR is applied to MAF during transients, then how is this different that using VE during transients...?

( notice here that VECORR is calculated during steady state, and that VE is steady state VE, and that MAF is steady state MAF )

This starts to prove my thoughts that even if we lower high speed Dyna air to 500/400 VE is STILL be used! EFIL does not have the parameters to truly disable VE (SD Mode). This is why I usually will do the VVE table to at least 3600-3800 rpms as I see that its blended into the final calculation.

Question is; is there a factor or weighting table that can control the amount of that correction being applied.......kind of like the octane scaler....

This is getting good.....

[GMPX]

EFIL does not have the parameters to truly disable VE (SD Mode).
Howard, if the MAF from a car has been tossed in the bin then what more can you do to force SD mode? i think you need to have a chat with Greg B again about MAF's.

[MikeOD]

This starts to prove my thoughts that even if we lower high speed Dyna air to 500/400 VE is STILL be used! EFIL does not have the parameters to truly disable VE (SD Mode). This is why I usually will do the VVE table to at least 3600-3800 rpms as I see that its blended into the final calculation.

Question is; is there a factor or weighting table that can control the amount of that correction being applied.......kind of like the octane scaler....

This is getting good.....

Did you ever research this anymore? I see that B8036 on my LS3 Camaro is set to 9590...and going on what I know about the size if the intake ports, manifold runners, plenum, and a rough guess at how much space the valves occupy in the ports...I'm actually really close to that same number...which also means that my car in particular, is roughly 35% larger in that department with ported heads and a FAST 102. I'm thinking about changing the value in B8036 by a factor of 1.35 and watching what happens...but I was hoping to read more from you about it if you've had any more time/opportunity to learn more about it.

[Tre-Cool]

Howard, if the MAF from a car has been tossed in the bin then what more can you do to force SD mode? i think you need to have a chat with Greg B again about MAF's.

Thread dig, but I think what howard is saying is that you can't disable SD (MAFLESS MODE) calculations, not enable it, which is what you do by unplugging the maf.

[ringram]

Thread dig, but I think what howard is saying is that you can't disable SD (MAFLESS MODE) calculations, not enable it, which is what you do by unplugging the maf.

Jessie and I were lucky enough to look over a GM Tech's shoulder who brought his calibration software to PRI to show us some stuff. Basically Jessie showed him some errors which he did not believe existed..

He came away enlightened.

Anyway there is most definitely a blend factor for VE vs MAF in the early ECU's in fact there are many many tables that we don't get to see. I think Jessie memorised a few offsets.

Im certain there will also be on in the E38 and E92 etc.