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HOWTO: Custom OS Speed Density via MAP - VE Tuning model for locked camshafts


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Problem: You have large camshafts with locked VCT (or a 5.4 V8) and are having trouble tuning the low rpm/low load portions of the map due to the non linear airflow characteristics (due to reversion and overlap) with the standard linear speed density model.

Solution: Utilise our custom operating system and the "Speed Density via MAP" speed density model. This replaces the speed density map (Inlet camshaft position vs RPM ) with MAP Pressure vs RPM like a traditional GM style VE model meaning you can now have a non linear airflow model.

To enable this feature you require the workshop edition and a 5 credit "Standard Custom OS". This is an extra 2 credits on top of a standard license.

First open the custom operating system wizard, select "Standard Custom OS" and press Next.

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You will then see a "Custom OS Options" page. Leave these items standard.

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Press "Check License and Proceed" which will then ask you to license the file, this will charge you an extra 2 credits (total of 5 for the vehicle). This will only be charged once.

You will now see a second set of Custom OS options (these can be changed as many times as you like). Select "Speed Density via MAP Sensor" for the "Speed Density Configuration" 

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Press Next then "Finish" and the file will automatically save and re-open.

Now navigate to the slope of map table within the speed density section where you can see the Y-Axis is now MAP Pressure (kPag)

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The next step to work out the home position of the camshaft and find the row which is close as possible with the new locked cams. If we look at the standard VCT configuration and assume the -10 row is the closest to where the new cams are installed we will copy this row to the entire map.

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You can see the first row (-10 VCT inlet cam angle) has been copied to the entire map. The speed density model will now operate as if the VCT system has been locked at the -10 position.

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If the airflow model was completely linear with no oscillations, overlap or reversion, eg we were still using the standard camshafts locked at -10 we would find that the AFR should now be perfect and flat across the entire rev range with the above table and no changes required.

As large camshafts have overlap and reversion at low rpm/load you will now find that the airflow model is no longer linear and you will be likely running rich at low rpm and map pressures. You can now simply tune this map like you would any traditional GM VE model vehicle. Eg to make it leaner at low rpm/load. Simply increase the speed density slope values at the cells you require. Remember that 101 kPa is approximate 1.0 load and anything above is boost.

This tuning style ONLY works with locked VCT or not VCT (eg 5.4 V8). If you try and use this model with VCT you will likely find yourself chasing your tail, especially if the VCT fails or operates differently in different conditions (eg when cold the VCT does not operate the same). This is because for a given MAP pressure your VCT position is not constant, therefore your model will be wrong and you must use the standard model which has a different row per VCT camshaft angle.

Lots of our customers have had a lot of success with this tuning model on large camshaft vehicles and we highly recommend it for large cammed cars which have rich/lean issues at low load/rpm.

 

 

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  • 5 weeks later...
  • 1 month later...

Hi I'm looking to use this method with locked vct, large cams and up to 40psi of boost.

Given that there are only 6 rows for the Y axis, am I to scale the Y axis in 10psi increments ie; 0 to 50psi ? I noticed that there are 8 cells when you go to change the axis values.

Also wondering which tables will reference the off boost driving etc.

Any help is appreciated 😁

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Depends on the cams. Basically anywhere you are getting aircharge going out the exhaust making the airflow model non linear. The only way you will know is via datalogging and seeing how the standard ve model falls over with large overlap. 

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The exhaust cam shuts the valve at 7 degrees atdc, tho that'll depend on the cam gear setting, so I spose it might be a bit more than 2000rpm. I'll work it out 😁

Edited by Puffwagon
Cos
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