I started using a piece of cardboard between my battery and the intake a few years ago, and it seemed to gave me about a 2 miles per gallon increase. (Though after building this, I received criticism that this will not help with gas mileage, but will help with performance!)
Now it was time for me to relocate my battery so now I have to make a Hot air block from scratch. I made this one from metal, and I expect better performance than my cardboard version.
This is the finished hot air block and my new battery box
I was using the stock battery mount location, with a normal tie down, but it kept having issues and getting loose. So then bought a replacement tie down, but that also came loose. I wanted to relocate the battery to the trunk, but I have way too many wires added in over time (inverter, fuel pump, 2x amps, and more). So I decided to relocate to about the same area under the hood, but lower and out of the way.
I have a b16 SIR2 that came with a y21 LSD transmission, but the case leaked and I replaced it with a more common s80 about 2 years ago when I rebuilt it. I added carbon lined synchros, new bearings, new rubber, new gaskets, measured and replaced as need, full rebuild.
I was driving on the freeway about a year ago and a piece of plate steel was pulled up by the wind, and busted a hole in my s80 transmission case. This is an article about how I got a replacement housing from the junk yard.
My car (1988 CRX HF) came stock with a Cable VSS (Vehicle speed sensor) on the transmission. The engine is a swap (b16a sir2, y21 transmission w/lsd) and was still using the cable VSS. After I installed the Integra cluster in the CRX, I needed to convert the car to Electric VSS.