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VE tables tuning.

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Hi, I think I got it wrong.

VE tables tuning is used for MAP based ecu? When you have MAF based you don't deal with VE.

I'm tuning MAP based ecu for my Vette 1985 (after MAP conversion).


This is correct. A VE based ECU doesn't use a MAF, although to confuse matters somewhat many factory ECUs such as those from GM use both a MAF sensor and a VE sub system and switch between these two ways of monitoring airflow based on operating conditions.

The easiest way to think of this is that a MAF sensor directly measures airflow. A VE-based fuel model on the other hand calculates airflow based on manifold pressure using the ideal gas law.

I am interested in how IAT is taken care of in A VE fuel model. My application will see very cold IATs - probably up to 40 C below the tuning temperatures, but as my Motec M130 has no IAT fuel compensation I presume that the value in each RPM/MAP load cell is not simply referenced to the MAP sensor but to a product of the MAP and IAT sensors.

If this is right the very cold air would call up the value in a higher load cell ??

Probably not a real issue as long as closed loop continues to work and is given enough authority but might explain why I destroyed some engines with an older ECU not running closed loop at high power settings.

If anybody could comment on the advantages of using a VE fuel system compared to MAF based control for a NA engine, I would be very grateful.

Rupert Clarke

Just to rough in some numbers for low air temps being important - the difference in air density at a fixed pressure of one atmo would be close to 10% between 15° and -10° C.

As far as I can see if a VE table does not include IAT in some way, a default to it should closed loop be turned off would be problematic.

Maybe I have missed something in Motec's M1 Tune methodology or my understanding of how VE tables work but not having IAT fuel compensation in the menus seems strange.


I have been trying to find you a MoTeC webinar that discusses this, but have come up empty -- they hint at it, but never state it clearly. The M1 ECU calculates the air mass based on the Manifold Pressure and the Engine Charge Temperature. The Engine Charge Temperature is calculated from the Inlet Air Temperature + Engine Charge Temperature Compensation. The Inlet Air Temperature is calculated from the Inlet Air Temperature Sensor (or falls back to Air box temperature if not available).

So, in the background, the mass of airflow is includes the compensation for density changes due to temperature, assuming the Inlet Air Temperature Sensor calibration is correct, and the Engine Charge Temperature is calculated correctly (it has the Engine Charge Cooling Gain, as well as Engine Charge Temperature Correction -- which compensates for varying temperature in the intake port that will affect the air temperature).

The complete air charge calculation is Engine Load. This is based on both constant factors (Engine Displacement, Engine Cylinders, value from the Engine Efficiency table) and the calculated Air Mass -- Inlet Manifold Pressure, Engine Charge Temperature and Engine Load Fuel Vapor Correction). See the help for this item as it list all the channel that contribute.

I suggest looking at the help in M1 Tune for these specific items:

Engine Charge Temperature

Engine Charge Temperature Correction

Engine Charge Cooling

Engine Load

Do you think the efficiency of your engine will vary with altitude? If so, there is a 4th axis available on the Engine Efficiency table that can be Ambient Pressure to provide altitude compensation. I would be very tempted to make any fueling changes based on logged data, go into a specific ambient pressure table. With that, you should be able to tune the basic engine on the ground, then leaving closed loop active, operate at different altitudes (different ambient pressures). Any noted fuel trims, can be then corrected by making that change into the appropriate ambient pressure efficiency table.

Thanks David for the very complete explanation.

I have stayed away from Engine Charge Temperature because I did not know how to measure air temperature within the induction manifold and my IAT sensor is very close to the throttle body.

The engine is not really required to make power below 3,500 rpm but I suppose that even with significant airflow there might be some heating of air before combustion. If there are any rules of thumb in this area which would help setting up this compensation I would love to hear of them.

I am using the 4th axis for ambient pressure compensation and have had some indications that even relatively mild lower pressure has a significant effect on increasing efficiency - presumably less back pressure on the exhaust system. However, I will need to fly much higher to really explore the changes.

Quite some time ago I think that you mentioned that you might be able to assist with creating a MAF based Engine Efficiency table using Motec's Inlet Mass Flow channel. If this was still a possibility or you know of someone who has gone down this road I would be very interested.

If you have a calibrated MAF sensor in the intake, you can verify that the MAF measured air mass flow (called Airbox Mass Flow) equals the calculated Inlet Mass Flow (just log both those channels and compare them). Any difference is due to the Efficiency Table, or Engine Charge Temperature Correction.

It would seem possible to build a package that actually used a MAF sensor for Inlet Mass Flow (there wouldn't even need to be a efficiency table, as that is only needed to calculate Inlet Mass Flow channel), and only as a fallback would use the calculated Inlet Mass Flow. In order to have this fallback reliable, you would do exactly what you are doing now -- tune it using the efficiency table and Engine Charge Temp corrections -- then compare the result to the MAF sensor.

Thanks again David.

I think that my MAF sensor (Subaru OEM includes IAT sensor) is set up as Inlet Mass Flow.

I attach an image of a data log file.

If I could run closed loop with a fall back to a table referenced to MAF rather than to MAP, that would be good. I understood that Motec provided the MAF channel for reference only and that it was not available for engine control. Perhaps a way around this would be to identify the MAF senor as the MAP sensor (with appropriate conversions ?).

I will have a good look at what I have and PM you. One issue could be longer duration valve lift which is a feature of a rebuilt engine I am expecting soon.

Attached Files

I would need to look at your M1 package, but I am confident that Inlet Mass Flow is the calculated value, and Airbox Mass Flow is the sensor value. You can confirm this by looking in Tools->Edit Input/Output Resources (search for "mass"), the only sensor resource you can assign is for Airbox Mass Flow.

You should add Airbox Mass Flow to your logging, and compare that with Inlet Mass Flow.

Hi David

You are right of course, the Airbox Mass Flow is the sensor and the Inlet Mass Flow the calculated ? value.

I am a newbie when it comes to understanding tuning and especially the M130.

I found our direct emails from last May and will see if I can follow your suggestions. I might wait until I have installed the new engine before seeking more assistance.

All the best.