what do these do for you?

 

let the valve covers breathe....

 

Valve cover breathers are generally used on engines that do not have "closed" positive crankcase ventilation systems. The LT1 includes a closed PCV system, and uses air that has been filtered and metered by the MAF sensor (94 and up only). That means that adding a "breather" will open up the system, and in effect create a small vacuum leak. Nothing the computer can't compensate for with the long term fuel corrections, but a "leak".

Blower motors generally need to alter or remove the PCV system, and a "breather' would be one of the options. But for an N/A engine, leave the PCV system alone. If you have worn rings, and are getting excessive blowby, the stock PCV system won't be able to handle it, and it will back up and blow oil into the throttle body. In that case, fix the problem, rather than adding a breather.

 

There is always some combustion gasses that pass by the rings. These gasses must be vented from the engine or else it'll build up pressure causing leaks, less effective ring seal, more parasitic drag on the rotating assembly, etc. The PCV system does this by venting the pressure back into the intake manifold to be ingested (before emissions were a concern they just vented to the atmosphere witha draft tube). Breathers allow these gasses to just vent into the atmosphere and are usually used in forced induction applications where there is greater blowby and the intake tract is pressurized.

The only bad thing about a breather (besides pollution) is they tend to make the car stink like engine oil. There's no point in using one unless you have to.