Positive Crankcase Ventilation Plumbing

[IanT]

Hi

My Rover V8 just has R/C breathers vented to atmosphere - I want to set up proper PCV though.

I've got the bits to bring air in through the air filter into right hand R/C.
Got a PCV valve from Real Steel (Fram) to 'pull' out of the left hand R/C.

I'll need to 'T' the PCV valve into the vac hose that runs from the Holley carb PCV port to the brake servo.

My question: sucking on the PCV valve offers very little restriction, so it feels as if I'm about to install a massive vacuum leak in the system! Do I need some kind of additional restriction in there somewhere?

[ian.stewart]

I would be tempted to put the breather hose to the top side of the carb and have a low pressure scavenge system, possibly plumbing it into the base of the air filter,
I would not advise fitting the breather to the vacuum hose for the servo as some of the oil/fumes will get sucked into the servo, Rovers are often heavy breathers and can dump out a lot of oil, the last thing you want to do if fill the servo with oil.
Ian

[stirlsilver]

I am about to fit an EFI manifold to mine and have found that there is two additional fittings on the base of the plenum (not including the one way valve for the servo). Would these hook up to the crank case breathers? Which I imagine would be a similar scenario as what IanT is asking? Should I feed the breathers to a point before the Throttle body rather then after?
Stirling

[ian.stewart]

My personal prefference is pre throttle, If you have a PCV valve failure or pipe fall off, the engine can start to lean out, The possible advantage of having the pipe after the throttle is you can get better ring seal from the vacuum created fron the post side of the throttle.
Ian

[JP.]

I use a 1" spacer below the Holley and this spacer has also a vacuum conection. This vacuum conection is used for my brake servo.
I use the pcv conection on the Holley for my crankcase ventilation system with a catch can between the lines and this system is working perfect.

Btw, I used a stock Ford PCV valve from a Sierra (all the same) and modifiet the valve cover to fit this. It was a simple job, just cut of the pipe and enlarge the hole in the valvecover to fit the Sierra rubber gromnet in and then stick in the PCV valve.


On the left side you can see the alloy catch can which leads directly to the PCV tube on the Holley

[stirlsilver]

So if I were to hook up the breathers post TB, I need a catch can and a PCV valve? I'm guessing it isn't smart to go without these two items? Ian your mention of better sealing is certainly attractive, since I am running the 12:1. They are new rings but hey the more help the better right? Obviously this does introduce more places for potential air leaks. Also one other thing? how do the crank seals find a vacuum? No problems?

[ian.stewart]

one of the "New tricks" that has come from US drag racing is crank case evacuation, using a specific pump for the application draws gas from the sump, and gives more power due to better piston ring seal.
crank seals wont be a problem unless you have a massive Vacuum in the sump, or use rope seals, I run 11.5 cr with just a catch can, I do get some oil in the can, but I dont have the baffle fitted below the take off pipe, so I expect that. and I dont run a servo either, servos are for GIRLS

[IanT]

OK, thanks for the answers.


I'm fairly convinced about PCV because it..
..draws nasty moisture & combustion gases out of crankcase
..can avoid crankcase pressure build up, and so..
..can help an engine to leak less oil
..stops oil mist from r/c breathers messing up your engine bay
..gives a less oily-smelling ride!
..is environmentally better


But it seems I ought to run through a catch can/filter to separate the oil vapour before 'pulling' the remainder into the carb base.


Going back to my original question (is a PCV valve a massive vacuum leak?) I found these explanations helpful, especially how the PCV valve operates under different vacuum conditions..

http://www.jalopyjournal.com/forum/showthread.php?t=181
http://www.jalopyjournal.com/forum/show ... =pcv+valve


And if you need a bit more info about running all-out crankcase vacuum pumps for racing, this page is a good read..

http://www.dragstuff.com/techarticles/vacuum-pumps.html

Cheers..

[barginbucket]

top jalopy jp,big respect,silly questions does it matter which r/c has the pcv in,does the catch can have to be a certain size/made of metal,sorry but i am mr layman,cheers

[leylandracer]

one of the "New tricks" that has come from US drag racing is crank case evacuation, using a specific pump for the application draws gas from the sump, and gives more power due to better piston ring seal.

What about this idea?Is it the same type of thing you was meaning Ian http://store.summitracing.com/partdetai ... toview=sku

The only problem Summit told me is if i am running a muffler(Silencer in english i think ) it will suck all the seals out For use on cars with NO mufflers you would think its the other way round

[leylandracer]

Just picked this forum up on the subject http://www.camaros.net/forums/showthread.php?t=16899

[GreenV8S]

On the standard 3.9 hotwire setup, there is a large breather connection to the throttle body (upstream of the throttle plate) and a much smaller restrictive connection downstream of the throttle. I believe the theory is that the smaller breather applies a gentle vacuum to the crank under part throttle, and under full throttle when there is no vacuum the breather just blows into the intake upstream of the throttle but downstream of the AFM.

On mine the trumpet base has three big outlets, one for the brake servo, one for the carbon cannister, the third unused and blanked off. It also has a much smaller outlet at the back which is connected to the fuel pressure regulator.

[stirlsilver]

I've temporarily set up a hose from the base of my TB to one of the tappet cover breathers and I have put a vacuum gauge on the other. The crank case breather is hooked up under the base of my air filter. My question is... In some conditions like idle i'm getting about 8-9 inHg or 4 psi of vacuum... Is this too much?

When it goes above 7 inHg I start getting some interesting sounds from what I beleive is the front crank seal which is new. If I drop the pressure down with a valve the sound diminishes but then I don't pull anywhere near enough volume when i start putting my foot down... As it is it pressurises with a direct connection without any restriction when I I start getting up it!

[katanaman]

Thats why your supposed to use a proper PCV valve as they automatically adjust the vac your getting.

[GreenV8S]

I've temporarily set up a hose from the base of my TB to one of the tappet cover breathers and I have put a vacuum gauge on the other. The crank case breather is hooked up under the base of my air filter. My question is... In some conditions like idle i'm getting about 8-9 inHg or 4 psi of vacuum... Is this too much?

When it goes above 7 inHg I start getting some interesting sounds from what I beleive is the front crank seal which is new. If I drop the pressure down with a valve the sound diminishes but then I don't pull anywhere near enough volume when i start putting my foot down... As it is it pressurises with a direct connection without any restriction when I I start getting up it!

I don't know what you're measuring. If you're connecting the breather to manifold depression then you need a restrictor somewhere. It could be that the hose you're using is small enough to act as a restrictor. If so, the pressure reading you get will depend on where along this hose you tap into it.