Air Die Grinder
For stripping the underside of my car to reprimer it after i got the undercoating off, i used a DA sander with a 6" diameter pad, and 80 grit, then switched up to 180 grit to smooth out the scratches, and just used my HF die grinder with scotchbrite roloc discs in the tight spots, then hand sanded the rest of it that those 2 tools couldent get to.
I plan on doing the same thing with my engine compartment. I have a husky 220v twin piston oil type 80 gallon compressor. I noticed a difference with my DA sanders. I have a HF brand and a bluepoint. The bluepoint tends to use less air, and the compressor cycles less.