I'm helping a friend put a new cam in his 383. Just an old DC .509 that has been on the shelf for 30 years. He last changed his oil 18 months ago with 10/30 VR1 and 1/2 bottle of GM EOS. He has less than 100 miles on the oil change. He insists that it will be fine to leave that oil in for the cam break in and change it out after 30 minutes. I am not totally comfortable with this, but I don't really see a reason not to. Any opinions on this?

Jeez, I'd at least pour the rest of the EOS in there and put a fresh filter on it - for cutting open & inspecting after break-in - and make sure the oil's topped off. But I'd prefer to see some fresh high-zinc oil and EOS in there.

He may get away with it but is it worth taking a chance of wiping a cam lobe ? Myself I would just put fresh VR racing oil and the zinc additive in and not worry about it. Ron

I don't think EOS (same as mopar crankcase additve) has zinc any longer as it has been reformulated for new roller engines with cats so not worth putting in. add some Comp Cam breakin additive and then another can after break in with a zinc oil like VR1.
Combustion byproduct build up in used oil may make it acidic I'd change the oil to some way cheap oil and filter with a can or two of break in additve. after break in 45 to 60 minutes total go New VR1 + comp cams additive.
my


PS install the cam about 102 to 103 to make it run good.

The new EOS supposedly does have less zinc; I recall the old stuff being phased out a while back and I bought all the old EOS I could get my hands on locally.