Discussion and questions related to the course Practical Standalone Tuning
if the VE table is based on TP as load (RB26 with ITB), do I need different fuel tables for different boost levels?
AFR target table is MAP based.
How does the VE table account for more boost = more air = higher VE ?
it will depend on the ecu being used some do a calculation behind the scenes and others need a 4d table created to add the extra fuel
It's a Link G4X.
In the Link ECU's you have a setting in the main fuel settings called "Equation Load source", if this is set to MAP then the injector PW is corrected 1:1 with MAP. i.e if you double the MAP the injector PW will be doubled.
Note the V in VE stands for "volumetric" - the effective volume of air in the cylinder doesnt change with boost, only the density or mass of air.
So, in theory the VE of the engine should change very little with boost, just this MAP multiplication will take care of the bulk of the fuel change required for a boost change. However with typical road car turbochargers when you increase boost you will find at higher boost levels the turbine will become more restrictive (especially at high RPM) which will consequently choke the engine and negatively effect VE.
So, with just the MAP multiplication you may find with some engine/turbo combos at high boost the lambda will drift richer than target at the top end. To correct this you can enable a 4D fuel table, put RPM and MAP (or MGP) on the axis, and use it to remove a small amount of fuel where required. I have only tuned a few GTR road cars and on the ones with a decent sized single turbo I didn't need any 4D correction, on one with small near-stock sized twin turbo's I needed a 4D table but it was mostly zero's with just some small -ve trims in the bottom right corner.