hi i just built a lt1 355 and i am just asking whats a good oil to use and i wanted to use synthetic but want to also know whats a good weight to use. has new everything no oil yet. thanks for any help

 

Use break-in oil to break in the camshaft and all the moving parts. Then I would recommend either 10W-30 or 5W-30, depending on your year make/model. Refer to your owner's manual for exact specifications

EDIT: I use Mobil 1 full synthetic in my car, a '97 3.8L V6. I have never had any issues and would recommend it to anyone

 

To begin, it's viscosity, not weight.

If you're using a roller set-up, there's no need to break any thing in. That was for flat tappets only. Break in oil wouldn't hurt any thing if you wanted to use that first.
5W-30 is what the car runs on normally, though 10W-30 won't hurt any thing. You should have a little oil in the car all ready IF you remembered to soak the lifters.

Personally, I'd buy some Royal Purple, Mobil 1, or Pennzoil and use that. I run Mobil 1 now, but will be switching to Pennzoil for my next oil change.

 

Royal Purple is overpriced for what it is imo. Mobil 1 and Pennzoil or both very good oil.

Anyhow like the above said on viscosity, and i know many like running 10w/30 in builds. I know some who run diesel oil in them (I have never done it, so wont recommend it).

 

The diesel oil is for the guys that are still running the flat tappet cams. It has the correct amount of additives for the cam and lifters. I use the Schaeffer's 15w-40 diesel oil in all my flat tappet motors and their 5w-30 in the roller motors. I like it more than any shelf bought oils. Check out their web page at Schaefferoil.com