Air Die Grinder

What is everyone using for an Air die grinder?

I have this el cheapo die grinder from Harbor Freight it claims only 4cfm @90psi, but there is no way. I have an Ingresol Rand 80 Gal 5 HP 15+ cfm @90 and my compressor can't keep up.

I used it to strip the hard places in the engine bay, but it was definitely a chore. The tool itself worked fine, it just seemed like it demanded a ton of air.

Any recommendations? I am going to be prepping the underside of the hood and trunk soon, so I will be using it for that.