UV without distortions?

Hello,
I am working on a 3000 - 5000 polyheavy Dodge Neon and I’ve got a problem with distortions on my uv-map.
Letting Blender unwrap the model didn’t satisfy my needs and I’m running out of ideas how to fix this.



This is my current map and I would like to keep this layout. Every part of the car (e.g. the feders or the hood…) is already seperated. I want to keep the lines as straight as possible, the out-of-place-polygons in the texture were my attempt to somehow retrieve a good level.
Here’s a picture of the model:


If needed I can share the model here.
Yours sincerely
Racer