Ok, look at this video.
As you can see at the timestamp of about 1:16 right as the race starts, the cars while they drive seem to emit some sort of plasma effect. How can I recreate that in Unity FREE version? I’ve messed around with particles and this is as close as I got-- not very close.
I cannot really see what you have in your image, but some things from my experience:
It’s generally a good idea to just set the emitter radius to 0 (since we want a straight ‘stream’ sort of effect), start them of fairly large, make them smaller over time and also, change color over time to make the alfa 0 at the end of their lifetime so it gradually fades out.
For added effect you can also use one of the flame textures that unity has for its standard particles, and set start rotation to Random between 2 constants and set the constants to -180, 180.
This should help you get a pretty cool looking plasma exhaust like effect, hope you will manage to make something cool!