Anyone using synthetic oil in a 500 ci engine ? If so, what brand, weight, (additives) & how is it working out ?
Any oil you buy today is going to be leaps and bounds better than what was available when the engine was designed and built so you could hardly go wrong with anything these days.
Nothing wrong with synthetic if you want to use it. I'm not sure that there is any real advantage unless you operate in freezing temps because you can get a wider range like 5w-40 but it also doesn't really cost that much more than regular in the grand scheme of owning and operating a classic car.
In the very early days of synthetics which were the 1970's there were issues with mixing it, changing back and fourth, and sitting for extended periods but with the current stuff none of that is an issue. You can go back and fourth if you want to. You can buy or make a blend if you are on the fence. If you have a good engine that doesn't leak or burn oil it still won't leak or burn it. If you have a leaker or burner it will still leak and burn it at the same rate as the same weight conventional oil it just cost you more.
Diesel oils are a popular choice and its not just a few crazy people like me the API (American Petroleum Institute) actually gives most of them the C rating for diesels as well as an S rating for gas engines. The S ratings are usually slightly behind the latest which in theory is good for older engines but just like gas the diesel stuff is also getting rid of the good/bad stuff so its not as clear of a choice as you would hope.
One thing I like about diesel oils other than I can have one oil that covers 94.324% of my fleet which includes diesels is the diesel oils are specially designed to deal with all the contaminants from the blow by that is inherent in all diesel engines. What do you get with a 50 year old engine design even if its in good shape? Blow by that contaminates the oil. I suspect that is one of the things they add to the 'high mileage' oils too is the same stuff to better deal with the contaminants.
As for brand if you have a brand that has been good to your family stick with it. If you have local store you like go ahead and buy their brand. If you find a sale go buy that brand. Like I said at the start even $1 store brand oil is likely way better than the best of the best in the 70's.
I use Mobil 1 15w-50 year-round in all of my flat tappet engines (Cadillac 472s, Chevy 350, Pontiac 400). It has the right amount of ZDDP, etc., and is available at Wal-Mart in 5 quart jugs for less than just about anywhere else. It has a 15W rating so can be used in colder climes as well.
As an aside, use the best filter you can --- WIX, NAPA Gold, avoid FRAM at any cost.
That is a pretty thick oil. For some cold areas. I don't use anything over a 40 except for in my vw bug.
Thanks Wayne