Have I topped out?
 

I think that I have at least until spring. My last 2 tanks in the Cavalier have been 43.9 and 43.5. I am hoping to maintain at least 40 MPG through out this winter. I put on a front end/bumper block last week end and blocked the bottom half of the radiator. I need to block the area between the top of the bumper and the hood. I also need to tweak my WAI. I have basically cut a section out of the side of the air box and blocked the other end. I need to rig up something to bring up the temps. Right now I am only running about 10-12 degrees above ambient temperature. I would like to see 20-25 degrees at least.

it is ironic that I am trying to give you advice since your mileage is above mine but take a look at my garage at my warm air intake and grill block.

also, I used generic weather stripping (automotive of course) to block the area between the bumper and the hood. something to look into maybe

*edit* another good garage to look at is "2003 cavalier" it belongs to phleas and he is in the top 10 with 60+ mpg. I stole some ideas from him myself.

I also see my mpg dropping now that the weather is cooling off.
Luckily it's almost coroplast season.

I assume "coroplast season" means after elections when candidates discard their signs. How do you identify which candidates are going to discard their signs?

If it says "Obama 2008" or "McCain 08", you can be pretty sure it's not going to be used again. ;) I doubt either of them will be running again in 100 years.

OIC. I haven't seen many coroplast signs for them. The coroplast signs seem to be all for local politicians who would generally plan to run again.

I finished up with my mods. At least for now. I used some rubberized foam for the gap in between the hood and bumper. I used some aluminum ducting for the WAI. Those 2 have bumped up my IAT about 25-30 degrees above the ambient temp. I added some pictures to my garage.