correct me if i'm wrong, but the reason you don't use synthetic oil for break in is because it has to much lubricity for the rings to file thierselves down on the cylinder wall. also, my engine machinst told me to replace one qt. of oil with ATF, since it has a much higher flash point then engine oil. I'm going to use 6qts Valvoline and 1qt ATF for my 383 break in.

 

No, there's definately enough friction with synthetic oil to seat the rings. The reason it's not used is because it's 3 to 4 times more expensive than dino oil. I've never ever had an issue with using synethic oil during initial startup.

 

i don't want to start an argument, but the rings will have a hard time seating correctly and if they start to seat it will take longer then conventional oil, and all that blow by is bad for the engine. cost has absolutley nothing to do with it. like MatLT1 said, engines from the factory are already broken in with conventional oil, but sometimes use synthetic right from the showroom floor.

 

Im no expert,but i would NOT put ATF in my oil...

 

that is the old school way of doing it plus atf has alot of cleaners so it will take out any kind for foreign contamination out. atf will not hurt the motor.

 

Exactly what i mean OLD school,10w-30 is all you need,if you really want to put an additive GM EOS an thats still not needed...jmho

 

Just because its old school does not mean its bad.
I use 15w40 in mine and it always ran better than running 10w30.
It always ran smoother and got better gas mileage also had better/stable oil pressure. Ever wonder why cam manufatures recommend 15w40? If you use atf in your motor just
Make sure you change it out after 50 miles.
BTW if you really want an OLDSCHOOL way of breaking in rings, mix a glass of ajax and water and run it down the throat of the throttlebody.
They did this in 1955 to break in rings on brand new Chevy Belaires so they would not smoke when they pulled off the lot. ATF is mid-school not quite old

 

Ive got a case of valvoline Im gonna use, 5W30. I was told to run it for 4-500 miles for break in, then I can switch to synthetic.

 

well, I have found out this:
run for 20 minutes, change oil
run for 50 miles, change oil
run for 500 miles, change oil
after 2000 miles total, change oil, dump in synthetic.
my bearing tolerances are so tight, the techs at work said I could use regular GM 5w30 oil to break her in, as its cheap and wont hurt anything... Thanks for the ideas though everyone!