PCV and crankcase vacuum

[gretchen/jason]

Is it better to have a negative pressure in the engine block by letting the PCV valve create a vacuum or to let it breathe through a breather in one valve cover .

 

Ive heard that a vacuum in the block is a good thing some people say its not a good thing just wanted a few opinions before i finis running a few vacuum lines .

 

Jason

[Pop N Wood]

Lots of discussion on this type of thing on LS1TECH.com.

 

For one thing, if you have it on a breather you tend to get underhood fumes and oil residue on the engine around the breather.

[dr_hunt]

Vacuum is definately a good thing in the crankcase IMO. Reduces oil aeration and helps ring seal. Vacuum pumps are not very practical on daily drivers but are a big plus on race vehicles.

[jnjdragracing]

If I remember correctly from one of your earlier post you are running a supercharger. If you can run a PVC valve that would help. Vacuum is a plus in the engine. On our supercharger with the cam we run, we can not use a PCV Valve. We have to use breathers in each valve cover and a evac system going to the header collectors. We really need to invest in a racing vacuum pump, but they are expensive for now, maybe later.

You are going to be pushing air into the engine from the supercharger pressurizing the cylinders (boost). You will have this pressure get past the rings and will go to the crankcase, so you will have to relieve this pressure out.

Try the PVC valve and see what it does, if you start blowing your dip stick out, then you will need some breathers in the valve covers or invest in a racing vacuum pump.

Hope this helps....

John

[Tombarace14]

Vacuum in the crankcase reduces drag on the rotating assy. Frees up alittle hp.

[gretchen/jason]

Well i do have a PCV valve hooked up but my brakes the "power booster " is also hooked up to the same vacuum line as the PCV valve . Doesnt seem to work so good for the pcv valve as it like to spit oil out anyplace it can at high rpms .

 

Not a lot of oil but just seepage . Im haveing a leak down test done monday but ive only got 6 k on the entire engine . .

 

I talked to a local drag racer and he said to just put breathers on each valve cover and not use a PCV as i use it as a daily driver . Or he said to put a T fitting of some sort to connect both breathers and vent them to a catch can .

 

I had the same problem on the stock 6 cylinder and it had 2% leakage by the rings , but spit crankcase oil at high rpms .

 

Jason

[naviathan]

The PCV system is in there for a reason. Heating and cooling oil combined with the carbon deposits created by the combustion chambers and all around heat creates an acidic gas inside the crankcase. If this gas isn't evacuated it will slowly eat away at the internal components of the engine. For a daily driven car it's a must. For a race car it's a safety thing. And yes it does reduce wear and pressure on the rings by creating a vacuum in the crankcase. Without it, the cylinder movement would create a positive pressure build up inside the engine that would put strain on the rings and the pistons when they make their power and intake strokes. This pressure can destroy rings, ringlands, cylinder walls and reduce overall performance. Keep a vacuum on it if at all possible. If not at least keep it vented appropriately.