I have comments about this in the
Tips and Tricks thread reagrding surface preperation. As stated there.... schools of thought are split on this but I'll comment on your particular application. Assuming parts that are going underneath the car, you could do worse by blasting AND backing it up with a good phosphate wash. Phosphate is after all, a cleaner as well as surface prep for some good grip. Probably something like this might help you (especially on that transmission case which will see the most abuse under your car). Degrease,sandblast,phosphate wash then powder coat. Yopu couldn't ask for much better adhesion than that. Not to mention..... the phosphate is relatively inexpensive and good for a long while. Personally, I've used it before and suggest you add that tidbit of insurance on your tougher parts
but that's just me. I hate doing things twice if it can be avoided......Russ