LS3 Vacuum lines
 

Where do the vacuum lines in the attached pictures connect? The orange one is at the front of the engine and the red one is at the rear of the engine

The top picture, are you referring to the orange cap that is on the steam port?
If so, that isn’t vacuum, that is a line that bolts to the top of your cylinder heads. It routes water out of the heads, and is designed to remove the air bubbles that get caught in the coolant system. Air bubbles in the coolant system turn to steam, and steam isn’t good. You need to direct a line from this to your radiator. Some guys route this line to the water pump, but all your doing there is putting the air bubbles back in the engine. If you go to the radiator, the air bubbles will find their way into your overflow via steam pressure in the radiator.

The rear red cap, looks to be on the intake manifold? Can you post up a better pic? If it’s on the rear of the manifold, just leave it capped. You don’t need it, unless you have vacuum operated accessories, such as an older a/c system that was vacuum operated, etc.

Scott is correct on both counts. I used the one in the back for my vacuum brake booster. I think it is a 1/2" fitting. I used a 1/2" TO 3/8" brass adapter fitting to convert the manifold fitting to my brake booster.

The steam line can go to either the radiator or plumb it into your water pump or heater hose lines. Will work either way.

Thanks Che70velle and 130fe, that clears me up yes the one with the red cap is on the intake.
I am an old school Small Block/Big Block guy still figuring out the LS thanks for your help ! :y0!: