When to start the use of synthetic oil

[1BAD351 21]

What mileage? I have heard 1500 is ok to switch over from organic, but then I have also heard to wait until 10-12k miles. What do you guys think? I am asking this for 2 of my cars, one being a new car engine (1993) the other being the 393 in my 69 if this matters at all. The one in my 93 has about 80 miles, yes 80 not 80k on the engine as of now, and my 69 has about 3k. Both have been run with organic since new, and I want to run amsoil in both at some point but don't want to change over to soon.

[6T9Mach1 12]

Depends on what type of rings you used, how the bore was honed and when the rings have actually seated properly. Could be anywhere between 500 miles and 3000 miles depending on the machining and components used. 2000 miles is a pretty safe bet usually.

[1BAD351 21]

Well the mustang I believe has regular iron (is that right?) rings, so the 3k miles on that is probably plenty then. My other engine has gas nitrated rings which I was told when I ordered the pistons from weisco that they had a 500 mile break in. So if I hold off until 3000 miles that should me more then sufficient?

[6T9Mach1 12]

If the manufacturer says that the break in is 500 miles then that should be what it takes if the machinist did his job honing the bores correctly. If at 500 miles the car has no blow-by and no smoke out of the exhaust I think that you would be safe. Waiting longer will never hurt anything, however. 3000 miles would be plenty in any case, as long as something is not wrong with the rings.