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.



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.