I believe it's not possible to use both, but I could be wrong.
What you're wanting is the "Real Fuel" feature where the car gets more power as fuel is burned (due to weight reduction), but that fuel usage depends on lap time rather than throttle usage. Is that correct?
Your best bet is to ask the SmartRace guy if it's possible. The Carrera system is designed for the car chip to do some of the work, the CU to do other work, and finally the race manager to do other work. There is some overlap between them, but I don't know if that overlap will allow what you want. Only someone with a deep familiarity with the software/firmware/protocol inner workings could say. @Yattr might know?

 

I did not realize that when I have the CU fuel settings turned on that it uses throttle to manage how much fuel is used. That may make the decision easier to just switch to that as an OK compromise.

Do you know if the other Smart Race Fuel Settings (time to pit and auto-slow empty cars) disabled when the the Lap Time Fuel Settings are disabled?

 

I don't think so, as I can't really think of why it would disable those features for that reason. I'd expect that SmartRace would either gray them out, or put some kind of note about it, or a popup when you enable Real Fuel mode. But, I don't use it enough to say with certainty. Hopefully one of the other regular users will chime in on that.

 

A quick test proved that the fuel settings within the app are an all or nothing setting. Once you turn off the Timed Fuel then none of the other settings work. I tried it this was for a bit, but not being able to set the pit stop time was frustrating. I have elected to stick with the settings found within the app because the benefits of that whole package far outweigh the realistic fuel settings on the CU.

Thanks for the help here gentlemen!

 

This is beyond my knowledge of the Carrera protocols. I dive deep but not into the App interface which is too slow for real-time monitoring and control.

Maybe the Smart Race developer can clarify.

In general, the CU is in control of both the App interface and buttons/switches and I can in vision that the Fuel switch might have priority…