Realistic or not, I'd like to modify several planes to smoke more and longer, both on startup, full throttle, longer larger contrails, and tire type situations.

 

Where would I start to look to tweak the smoke?

 

Or perhaps there is a utility app somewhere for this?

fx files.

 

Located within the FSX/effects folder.

 

This contain all the information on startup smoke and contrails and can be edited. The aircraft.cfg for each aircraft will tell you which fx file is used during startup.

 

If you have the SDK installed you can use the fx tool to edit fx files within FSX which makes life a lot easier although they still can be confusing things to do.

Note, that especially the longer contrails can have an impact on FPS, especially with many AI planes flying around.