My main goal concerning the frame was ensuring its integrity and protecting it from as much corrosion as possible. As shown in the walk through on body separation, I was fortunate in that my frame had moderate surface rust. There were still areas with plenty of paint. The worst area was the rear of the frame, especially the top and back cross member. There was some pitting but no holes or thin spots. I also noted no tears or deformations anywhere else. Before I could coat the frame I had to decide whether any modifications or improvements were in order.
STRENGTH: There are things that can be done to the frame to improve overall strength. Plenty of literature exists on adding gussets, completing stitch welds, etc. I learned that Stingray frames from 68 - 79 are pretty stout, and the later models already have the stiffeners added to the kick-ups. Most importantly, I learned that for my target torque output of 400 - 450 ft-lbs, the unmodified stock frame was sufficient. However, did decide to add the spreader bar between the front shock towers because it's a relatively easy, inexpensive way to reduce flex in that area.
COATING: I focused on cost and protection over aesthetics. While I care what the pain job looks like, I'm not going to worry over some brush marks and runs on a daily driver. I found plenty of factory runs in the paint job anyway. I expect the paint job to get abused, and without ready access to a paint booth, I opted for foam rollers and small brushes. At the end of each season, I will touch up the frame as needed. By letting it cure over the winter, I should be able to maintain a good protective coating. With this strategy in mind, I chose a product called Zero-Rust. You can read about it on their website, but basically Zero-Rust is a DTM (direct to metal) enamel, high solids paint / primer with phenolic additives to bind with rust. According to the product label, you remove any scaling and heavy rust, spray with the pre-prep (supposedly increases adherence), and paint away. Some folks use POR-15, but my understanding is that the prep work has to be immaculate and the isocyanates make it more difficult product to work with.
I passed on powder coating due to cost and concerns about the maintenance of the finish. I don't possess the tools to powder coat a frame. I didn't get any quotes, but I understand it's fairly expensive. A Stingray sits so low, it's not difficult to imagine the frame scraping against a speed bump, steep driveway, or pothole. In this case, I'm pretty sure some powder coat will scrape off. I'm not so sure it can be easily put back on. I suppose it's possible to clean and prep the surface, ground the frame, spray the powder, and use an IR lamp to locally heat the area. That seems like such a major effort. I've read where others have sanded the powder coat and painted over it, but I haven't heard how well the paint adheres to the powder coat. Paint just seems easier to maintain in this application. I'm sure others disagree...
There's not much to tell. I used Purple Power to clean off 30+ years of grease, oil, and dirt. Then I used paint stripper, wire wheels, and flap disks to remove rust and paint. This takes more time than you would expect because of the nooks and crannies (especially the trailing arm cavity, motor mounts, and shock towers)
As you and see from the picture, I was very lucky regarding the frame's condition. There was no holes, rotting, or deformation. The worst corrosion was some minor pitting located in the rear near the bumper shock mounts, most noticable in the lower left part of this picture.
I thinned the Zero-rust 20% with Xylene and applied it with a foam roller or foam brush. The first coat covered well and seemed very tenacious, especially where the rust was located. The second coat (red) didn't cover over the black as well. It seemed to smear over it instead of bind with it. I think the problem may have been my approach. I let the first coat cure for a week, but it still clumped on the sand paper. If I have one complaint with Zero-Rust, it takes a long time to dry. It's also possible that 20% was too thin for the second coat. Either way, I was finally able to get a second coat on, but I had to go over it twice to get complete coverage. The picture shows the contrast between the red and black coats, and that really helped me ensure complete coverage for all coats.
The third coat went on better than the second. I thinned it less, which could have accounted for the difference, or it's possible the black paint covers better than the red. A week after applying the third coat, I used a thin blade box cutter to shave the extra paint that accumulated around the frame holes as well as any major drips that had formed. After two weeks, I hung the from the chain hoist to let it cure over the winter.
The final picture shows the spreader bar upgrade. I was pleased with Zero-rust's final gloss, and there is only slight color variation between the frame and powder coated control arms.
SUMMARY: I'd give this job a 5 out of 10 the way I did it. The paint and rust removal took a long time. If I did it again, I would buy (or rent) a pot blaster and bribe one of my friends (with beer) that live in the country, and blast the frame clean. It would've saved a lot of time.