The M30 puzzle of the day - question

[Jeff N.]

Martin was supposed to post this but I guess he's got CRS syndrom...

Soooo....on the M30...there's a 3mm (?) vacuum line that runs from the base of the intake manifold and T's into the valve cover breather hose.

What the heck is >that< for?

Jeff

[Hector]

we can enjoy the buzz with this other question. Hope you don't mind the piggy-back ride or intrusion, Jeff. For the m30, what is the purpose of the hose (similar in size to the fuel line) coming from the bottom of the intake manifold, connecting to a dangling white L-shaped or elbow connector with another piece of hose hooking this elbow to the master cylinder, I think? What is the purpose of this elbow anyhow?

[Jeff N.]

That's a vacuum check valve. Sits 'tween the intake manifold and booster. Keeps air from leaking back into the engine when you go from a low vacuum to high vacuum situation within the brake booster.

BTW, insidious place for a vacuum leak. Make sure the takeoff is capped and there are no cracks in it (like mine had a long time ago).

Jeff

we can enjoy the buzz with this other question. Hope you don't mind the piggy-back ride or intrusion, Jeff. For the m30, what is the purpose of the hose (similar in size to the fuel line) coming from the bottom of the intake manifold, connecting to a dangling white L-shaped or elbow connector with another piece of hose hooking this elbow to the master cylinder, I think? What is the purpose of this elbow anyhow?

[Bill R.]

closed, say your coasting down from high rpm, then the crankcase ventilation system doesn't suck anything if it depends on vacum in front of the throttle plate.... but by tapping into manifold vacum with a small tap is supplies a little suction to the crankcase whether you're accelerating or decelerating.... It always keeps some suction in the crankcase.... So, is there a prize?

Martin was supposed to post this but I guess he's got CRS syndrom...

Soooo....on the M30...there's a 3mm (?) vacuum line that runs from the base of the intake manifold and T's into the valve cover breather hose.

What the heck is >that< for?

Jeff

[Paul in NZ]

your prize is our undying gratitude,adulation,and awe of the depth and breadth of your knowledge and your willingness to share with us

[Jeff N.]

The Baconator swears his car runs better with the openings plugged. He's mumbling something about vacuum leaks and all that. Must be the large amount of blowby he's got...messing with his mixture and all..

Sooo...short of sucking out noxious gasses out of the crankcase and pumping them back into the engine, is there any other point to keeping a slight vacuum in the crank case?

What would happen if you plugged up that vacuum line in question AND the valve cover cover inlet into the intake? Run the valve cover vent to a catch can or similar... You'd have neutral to postive crankcase pressure and no connection of the intake track to the engine.

...prize? Wazzat?

closed, say your coasting down from high rpm, then the crankcase ventilation system doesn't suck anything if it depends on vacum in front of the throttle plate.... but by tapping into manifold vacum with a small tap is supplies a little suction to the crankcase whether you're accelerating or decelerating.... It always keeps some suction in the crankcase.... So, is there a prize?

[Bill R.]

The crankcase ventilation system which started out as a pollution control device has turned out to be nothing but good, there is not downside to it.. by scavenging all the combustion gases and unburnt fuel that gets down past the rings and scavenging condensation.. it keeps the bearing alive much longer , same for the other parts... no acids, no sludging ..
Removing the crankcase ventilation system is one of the last things i would do... jmo....
Also when you get postive crankcase pressure then is when the front and rear seals go... and if the engine is tight then its not a very big vacum leak anyway...

The Baconator swears his car runs better with the openings plugged. He's mumbling something about vacuum leaks and all that. Must be the large amount of blowby he's got...messing with his mixture and all..

Sooo...short of sucking out noxious gasses out of the crankcase and pumping them back into the engine, is there any other point to keeping a slight vacuum in the crank case?

What would happen if you plugged up that vacuum line in question AND the valve cover cover inlet into the intake? Run the valve cover vent to a catch can or similar... You'd have neutral to postive crankcase pressure and no connection of the intake track to the engine.

...prize? Wazzat?

[JoeS]

how I interpret BillR's post is that the vaccum line pull comes from the intake manifold and into the valve cover.

I thought the vaccum pull went the other way ...were the vaccum pulled from the head into the intake manifold.

I thought this because how else does the oil shitty fudge get inside your intake manifold. The air that comes thru the air filter should be relatively clean. shouldn't it?

[winfred]

i think a slight vacuum helps the rings seal better also, years ago i read about a dyno test where they installed a pump to vac down the motor while doing a pull, it had good results up to a point, it was so long ago i can't remember how good it was

[Jeff N.]

i think a slight vacuum helps the rings seal better also, years ago i read about a dyno test where they installed a pump to vac down the motor while doing a pull, it had good results up to a point, it was so long ago i can't remember how good it was