I noticed this yesterday when I was finishing off the Weekly Forzathon Challenge and I haven’t seen it mentioned explicitly in any of the Known Issue Categories.
If you apply the RWB Widebody Conversion to the 1973 Porsche 911 Carrera RS then add any Turbo with Anti-Lag then the Backfire and Flames stop appearing, it still makes the sound of the Anti-Lag but there’s no flame.
It works fine on the Car without the Bodykit but as soon as you put it on then the Backfire disappears no matter your engine.
Testing it with the 4.0L F6 Engine Swap and Race Twin-Turbo+ Anti-Lag:
Going into Freeroam to see if this is just an anomaly in the garage (it’s not):
Trying it with the Stock Engine and Race Twin-Turbo + Anti-Lag to see if it’s just an issue with the engine swaps (it’s not):
Starting with the RWB Bodykit and then switching removing it which makes the backfire appear (this was with the stock engine but it’s same situation with the swaps):