crank case breathing

[DRAGIN]

i realize the lt1 is a closed type system but couldn't the motor be helped out with valve cover breathers, or an evac system. i am not in any sort of area at this time to worry about emissions testing. in my mind freeing up the pressure in the crankcase could really help?please educate me on this?
thanks

[Injuneer]

What's wrong with the closed system? If effectively removes the crankcase vapor, and disposes of it by burning it in the engine. It does this priimarily at conditions other than WOT, so there is no negative affect on performance.

If you "open" the system, and use a breather rather than the hose from the throttle body to the passenger valve cover, the only thing you are changing is the source of the air that sweeps through the crankcase. The factory system uses filtered air, and in the case of the 94-97 models, air that has been though the MAF sensor, measured, and counted toward the total air flow into the combustion process. Since it ends up in the combustion chambers, the PCM can add exactly the amount of fuel required to match the air flow.

A breather would let "unmetered" air into the combustion process, causing a slight lean condition. The long term fuel corrections would compensate for this extra air flow by adding extra fuel for the unmetered air. The elevated long term fuel corrections for Cell 15 will be used at WOT to fuel the engine, even though there is very little air flow through the PCV system, because there is very little manifold vacuum. Now its running slightly rich at WOT, because of the elevated long terms.

Not a big deal, but if the stock system works, why destroy it? A lot of people will claim the system is defective, and puts oil in the throttle body. A properly functioning system, in an engine without excessive blowby will not cause oil to enter the throttle body. My PCV setup is completely stock and functional, and can handle the blowby from an 800HP nitrous motor, with no oil in the throttle body.

A vacuum pump evacuation system would add weight, and consume HP. Makes sense on engines with certain ring/piston clearance setups, where high crankcase vacuum can increase HP, but not on a moderately modified engine. Here's a vacuum pump setup on a 383ci SBC - but its a blown engine, making 1,350HP at the flywheel:



Do you want to add all that extra weight to your engine?

[Rob B (shoebox)]

Fred always gives great explanations.

For most applications, the stock system is better than any breather could ever hope to be. The PCV system gives you a scavenging effect you don't get from a breather.

[sneitzel]

Fred always gives great explanations.

+1 to that...

[DRAGIN]

ok i get the point

i will try the factory system before just trying too re do it thanks guys for the help