2 Bar tune with returnless fuel system ?

[DrX]

As my FPR is not boost referenced, the only way that the returnless fuel system has to compensate for decreased injector flow under boost is to keep the injectors open more. Hence those of us with this setup should see higher duty cycles and max out the injectors sooner if properly tuned.

If 1 psi of boost equates to a loss of 1 psi of FP and my actual FP(line pressure) also drops 5 psi under boost, that is like losing 13 psi of FP at 8 psi of boost! From my calculations that works out to at least +13% duty cycle at the corrected flow rate of 37 lb/hr(Radix 42LB injectors).

Now, I don't see anything in the tune where I can correct the IFR for boost or the line pressure drop. Magnuson has the IFR set to 5g/s for all MAPs pre boost but there is no table for boost. So as there is no feedback in Open Loop, I assume that there is no compensation for the decreased IFR other than programming a richer "PE modifier based on RPM" or “Boost VE” table of EFILive's custom OS than what you actually want to achieve if you go MAFless. Does this mean AutoTune is not an option for me?
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[Blacky]

This is how I understand it to work, I am not a tuner - so anyone feel free to correct me.

You summed up the IFR under boost well, and as you say, there is no boost adjustment for IFR. AutoVE tuning should still work fine. The VE values that are produced will have compensation for the lower flow rate "built in".

You will see higher VE values under boost, simply because the engine is under boost, but you will also see higher than expected* VE values under boost because those values are compensating for the reduced fuel flow and will be calculated higher in order to artificially increase the IPWs to maintain the commanded AFR.

*Expected, meaning expected VE values if the FRP was referenced to boost, or a boost IFR table was available.

Regards
Paul

[DrX]

Thanks. Should have figured that out myself.

I was also not certain that Auto VE could be used to tune for boost(I was following the tutorial). I have modified the BEN Map(added MAP labels to 200 kPa) to log when in boost also and it looks like it will work.