There isn't just one zinc-phosphorous compound that is used in motor oil. There are many. Mixing them may result in the two additive packages reacting to each other and precipitating out, leaving you with less ZDDP than the original oil started with.

Another factor to consider and is activating temperature. The different compounds react at different temperatures and have been selected by the oil company technical staff to fit a particular use.

The next factor is detergent level. Race engines come apart all the time so the oil has much less detergent. This frees up some surface for more of the zinc compound to attach to. But our engines tend to stay together longer, also are not driven enough to get oil hot enough to drive out moisture. Moisture acts as a catalyst and causes formation of different molecules, like varnish. So in a street rod type of car one needs much more detergent.

If price matters, I suggest using a good fully synthetic oil designed for your typical usage and running it twice as long. The cost difference will be negligible. Most of us are throwing away several quarts of perfectly good oil every year by changing the oil at the "magic" 3000 miles. I challenge you to run oil for 6,000 miles and send it to Blackstone Labs or similar for analysis. It doesn't cost that much. Nearly every time you will get back an OK to keep using the oil. Shoot, over the road trucks go for 100,000 miles or more between oil changes. Their duty as far as loads on bearings and cylinder walls is much higher than 97% of our rides.

I prefer Joe Gibbs Driven because they have done the research. Others can be just as good, but how can you tell?

R.