I just noticed that there's no cover over the 4 header pipes (Honda part# 18120-PCX-010) on my 2002 AP1. Did it ever have one or did it get lost along the way somewhere?

 

Yes all cars came with them from the factory, are you sure you still got the oem header installed?
Most aftermarket headers can't fit the oem heat shield.

 

Hmm, that's a good thought. I don't believe it's aftermarket. I've been the only owner of the car and the only place that's worked on it and tuned it didn't mention putting an aftermarket header on it.

There are two bolt holes there which made me start looking to see what they were for. That's when I realized that there should be a cover.

 

I wonder how much a cover affects the temperature of the engine bay?

 

I think it was designed to protect the battery from heat.

 

The battery has another shield so don't think it's in danger without it but I would get a new one fitted anyways.
It will lower the engine bay temps some and maybe keep the exhaust temps a bit hotter for more power
Should not be to hard to find a nice looking used one cheap.