How to add afterfires?

just a simple question, I’ve been trying to add afterfires to vehicle that don’t have afterfires, but I don’t know how to do it

 

You need to modify both the exhaust and engine.
The exhaust and/or engine should have nodes that look like this:
["exh10",-0.06,2.35,0.3{"afterFireAudioCoef":0.55,"afterFireVisualCoef":0.4}],
["exh11",-0.127,2.35,0.3{"afterFireAudioCoef":0.55,"afterFireVisualCoef":0.4}],
Probably the same nodes that are used for the exhaust smoke for which ever vehicle you are changing.
The part that defines the engine characteristics needs to have these lines under the "mainEngine" section:
"instantAfterFireCoef": 0.75,
"sustainedAfterFireCoef": 0.75,