Saturn Ion aero...
 

So I’ve got a tough question for you guys and maybe you can help... I can’t find the drag coefficient for my Saturn Ion sedan... I read that the coupe was 0.31 but I’m not sure about the sedan... I know that the coupe front end can be swapped onto the sedan(and it looks better IMO) but would it help aero? It looks sleeker... ideally I would do it with the Redline bumper cover which would eliminate the upper grille opening completely and be a little lower and it’s lower lip is reminiscent of a splitter...

So I also read that apparently the sedan has a Cd of .32, so for aero alone it isn’t worth swapping to the coupe front end, at least when you factor in ROI

It looks like you answered your own question.

Have you thought about mods you could do without the front end swap or Redline bumper cover? I haven't looked at an example, but I'll bet there is something that can be done.

I was mainly considering the front end swap for aesthetic purposes, but I also imagined that it would be sleeker, given its looks...

In theory if I sacrificed my Redline instead of giving it yet another engine, I'd have all the front end parts I would need for free, but I couldn't give up my LSJ powered rocket ship lol

Right now I've got some grille blocks but I eventually wanna do all the things I had done with the Malibu(rear wheel skirts included)...

I would also like to do a set of ventilated fenders(like OG VX) and a full undertray

You may find the biggest gains may be working on the air flow over the rear. Every little bit helps.

I’m thinking the same thing... I noticed nothing when I lost my front belly pan, until I changed the oil lol... I think I’m gonna work on a deck lid extension and then maybe a diffuser if I can get it done with the other projects that need attention

decklid
 

You might consider GOOGLING a 'blueprint' of the Ion,then place it under the Template tool,available on the Aero Forum page.
This could help with sizing of the decklid extension.
The Ford 999,Chevy Ecotec,and VW Jetta hybrid land speed record cars,all used this sort of elongation.
Extending the C-pillars to the end of the decklid,as flying-buttresses would also help.It does create a blind-spot on the passenger side,but you can overcome this with judicious use of the side mirror.:)

You gave me a great piece of insight here... I hadn’t thought, but there was an Ion Redline that was campaigned as a land speed car, using a turbocharged LSJ to hit like 212 MPH...

https://www.wallpaperup.com/118323/2..._tuning_f.html

While I imagine that design of decklid extension is effective, it’s huge... I was initially planning 4” or so which I don’t think would require use of anything beyond a sturdy plastic(not necessarily coroplast)...

huge
 

Granted,it's out there! The thing is,that there's a length at which the end of the body approximates where the non-mutilated body would intersect the ideal pathway profile,whatever that may be.
The LSR Saturn may reflect that length.Don't know.Only a template comparison will illustrate something that's basically optimized.

Given that I’m browsing this with an iPhone and not a laptop I’m not sure how well I could photoshop a side view Ion sedan over the template to see how much lip I would need... I do see where you’re at though... would it be a case of “some better than none” or “all or nothing”?