pcv on steroids?

[Anonymous]

a few weeks ago at a car show saw a v8 that had hoses running from the vavle cover vents (pcv holes) down to a nipple that had been welded to the header collector. the owner called it a crank case evacuation system.
has anyone see this are you familliar with this kind of setup what are the pro's if any and the con's if any. would this be usefully for a big six. just wondering. thanks

 

[Asa]

i'm not even sure if that would work...

there's not even any vacuum on the exhaust, so how would that evacuate the crankcase? there's pressure from the exhaust, i think it would do the exact opposite and fill the crankcase with exhaust....

but i'm not sure of it

 

[Anonymous]

thats why it seamed wierd to me but i thought maybee i just didn't under stand it. it is interesting though id like to know more about it.

 

[Asa]

here's a question, was it going straight into the exhaust, or was it at an angle?

here's why i ask
http://community-2.webtv.net/PAGEBUILDE ... VACUATION/

 

[Anonymous]

yea thats it. so whats the deal. and what is the thing welded on it's kind of ball shaped then forms a nipple forgot about that.

 

[Thad]

The "thing" being welded in the exhaust is a check valve for a smog pump. There is a venturi effect in the hi velocity area of the collectors.
Yes it will pull a vacuum in the crankcase, have seen 24 inches pulled while dynoing an engine.
Vacuum equals "thinner" air in the crankcase, less resistance to pistons coming down, crank turning and less air to suspend oil around the crank.
Great for drag racing engines

Useless on the street, seen several people try, too much back pressure in exhaust system. Have seem a smog pump rigged as a vacuum pump to the crankcase. It was sold as a kit.

 

[xctasy]

These set-ups are used to reduce ring flutter past 5000 rpm. The sump has up to 3, mabee 4 cfm of blow-by form the rings on a stock305 V8, and well over 6 cfm on a wide clearnced small block reving past 6000 rpm. The blow by is a necessary evil. Ring flutter looses power, but running gapless rings causes ring land damage and other negatives. The key is to use the tightest ring cleanace that doesn't loose power. Failing that, set it loose, and use an evacusump set-up, with a check valve to direct to the exhast. Thats 6 cfm pressure going to the exhast, not pollutiong the intake charge. It's a WIN, WIN.

Turbos, old cars, or race engines with worn rings are helped by these set-ups.

It was a common thing on Pinto OHC's, David Vizard documents it fully.

 

[Anonymous]

The "thing" being welded in the exhaust is a check valve for a smog pump.

Yup when there is too much back pressure it keeps the exhaust from going into the smog pump and messing it up .

 

[Anonymous]

so i guess it may or may not help but it wont hurt anything right.

 

[Thad]

Street machine with mufflers no real gain if any. For drag or road racing need to know were to locate so that anti-backfire valve in the right place.

 

[Anonymous]

Mopar cars from the late '70s and early '80s had these as OEM equipment, and they worked great for evacuating the crankcase. But as Thad says, at normal street RPM, they won't give you more than maybe a hp or 2.

Whole 'nuther story on a race engine though. Suck 24" of vacuum out of the case and you are looking at dropping the internal case pressure from 15 psi (normal atmosphere) to 3 psi. That means that 80% of the air that the pistons had to move up and down in the case is no longer there. Above 5000 RPMs that could easily be worth 5-10 hp. Less air means less frothing of the oil too, resulting in higher oil pressure and lower oil temps. It's all good!