Sal..Zep purple is their purple degreaser. Also sold by the gallon, usually right next to the Citrus. It is strong and caustic stuff. You DON'T want to breathe it, trust me. I am usually puffing on a cigar whilst doing the wheels so I don't have to smell it. But, to answer your question, the purple is their strongest APC. It is used to degrease engines primarily as it has the cutting power of a diamond drill bit. I really only use it for tires. It will make the brown stuff come out of the tires just like ARO will, for a lot less money. If you need the absolute strongest APC you can have for a certain job, the purple is it. It is about $3. more expensive a gallon than the Citrus. I stock both and use both. I go through a lot more Citrus than purple. I cut the purple 4:1 like the citrus. Hope that helps. As far as the 501, I'm not surprised. It's some neat stuff, that's for sure. I had never used it with an aggressive pad before, usually just white or less, and I was very pleased at how it came out. I don't think I'd try that on a soft black paint though. Misha, it really doesn't compare to anything. If I were to compare it to any product, I think it would be XMT 360 which is also a favourite of mine, especially on very nice chrome. It has wicked cleaning ability as well as a strong sealant component. Topped with 601/105, you're gonna have unbeatable protection.
