Boost check valve in the pcv system

Discopotatoes · Post by **Discopotatoes** » Fri May 18, 2012 4:45 am

Hi all,
Which after market check valve is best used to stop boost entering the crank case? It will need to be good for upto 20 psi

Cheers
Disco

DEVONMAN · Post by **DEVONMAN** » Fri May 18, 2012 8:07 am

Discopotatoes wrote:Hi all,
Which after market check valve is best used to stop boost entering the crank case? It will need to be good for upto 20 psi

Cheers
Disco

I had a brake servo non return valve in line with the PCV up until recently and it seemed to work ok. However, I have now dispensed with the PCV altogether and just rely on the pipes from both rocker covers into the neck of the aircleaners just before the turbos inlets. Ideally a catch tank should be in the system.
I removed the pcv valve as it cause erratic idle at times.
If you use a check valve with a pcv, it needs to have a fairly weak spring so that you get some air flow at all NA situations but still closes just as FI begins.

The only problem I have with my set up is that crankcase air emits from the dump valves at gerachanges and an air tight firewall is necessary unless you like the smell.

I could use recirculating dump valves of course

Hope someone else can identify a suitable check valve for you.

Cheers Denis

mgbv8 · Post by **mgbv8** » Fri May 18, 2012 10:47 am

When the boost comes in, isnt that when you need the most crankcase ventillation ??

If you put a check valve in there because the pcv is is connected to the boost side and then close it off on boost where do the blow by escape to?

I can understand the check valve in the servo line.

Sorry if I'm being a numpty here!

Why dont you run the pcv lines to the air inlet somewhere, or via a catch can to the inlet?

I ditched my pcv years ago before I got blown. Just large lines with inline filters is all I had via a catch can and ran the vent pipes out through the inner wings.

kiwicar · Post by **kiwicar** » Fri May 18, 2012 10:59 am

Hi Perry
I think spot on mate, in this situation I would run it all to the inlet side of the blower.
Best regards
Mike

Discopotatoes · Post by **Discopotatoes** » Fri May 18, 2012 3:39 pm

My set up at the moment is using just the flame trap on the rv8 so I don't believe there is a one way valve in that part of the system, I do need one on the brake servo side,
I agree with having it vented to the non pressurised side of the turbos under boost via a catch can, but if I had a check valve at the plenum as well that would stop boost entering and allow pcv to work normally under vacuum when the car is cruising.
So the blow by gasses are only entering the turbos/inter cooler when on boost
or am I over complicating things?

DEVONMAN · Post by **DEVONMAN** » Fri May 18, 2012 4:53 pm

It's more a refinement that a complication.
Feeding the blow-by gases into the suction side of the turbos will of course speed up clogging of the intercoolers and reduce there effectiveness. I clean mine out about once a year to remove the oil film.
The pcv valve operating at cruise will minimise this problem.

But you could just do as Perry says and dump the gasses out to the underside of the car via a catch tank. (Normal practice back in the 60's and & 70's)

Cheers Denis

mgbv8 · Post by **mgbv8** » Fri Jun 08, 2012 9:10 pm

DEVONMAN wrote:It's more a refinement that a complication.
Feeding the blow-by gases into the suction side of the turbos will of course speed up clogging of the intercoolers and reduce there effectiveness. I clean mine out about once a year to remove the oil film.
The pcv valve operating at cruise will minimise this problem.

But you could just do as Perry says and dump the gasses out to the underside of the car via a catch tank. (Normal practice back in the 60's and & 70's)

Cheers Denis

Nice and simple eh mate ??
Works for me

Discopotatoes · Post by **Discopotatoes** » Thu Oct 04, 2012 10:48 pm

I now have both rocker covers at the front venting to atmosphere and a small filter on the breather at the back of the nearside rocker cover, but still get a leak under boost at the rear of the block from the Valley gasket I believe.
Do you think feeding the gasses from the rear of the rocker covers aswel to the turbo inlet would sort this?
I have had the valley off to try and cure the leak but to no avail!

DEVONMAN · Post by **DEVONMAN** » Fri Oct 05, 2012 7:05 am

Discopotatoes wrote:I now have both rocker covers at the front venting to atmosphere and a small filter on the breather at the back of the nearside rocker cover, but still get a leak under boost at the rear of the block from the Valley gasket I believe.
Do you think feeding the gasses from the rear of the rocker covers aswel to the turbo inlet would sort this?
I have had the valley off to try and cure the leak but to no avail!

I don't know what engine you have but if you have an early 3.5 engine there is a breather connection in the block at the rear of the off side rocker cover. Are you sure this is not leaking or just open as it will allow oil out from the valley.

Discopotatoes · Post by **Discopotatoes** » Fri Oct 05, 2012 3:17 pm

DEVONMAN wrote:
Discopotatoes wrote:I now have both rocker covers at the front venting to atmosphere and a small filter on the breather at the back of the nearside rocker cover, but still get a leak under boost at the rear of the block from the Valley gasket I believe.
Do you think feeding the gasses from the rear of the rocker covers aswel to the turbo inlet would sort this?
I have had the valley off to try and cure the leak but to no avail!
I don't know what engine you have but if you have an early 3.5 engine there is a breather connection in the block at the rear of the off side rocker cover. Are you sure this is not leaking or just open as it will allow oil out from the valley.

It's a late 4.6 cross bolted block, I have not seen any connection in that area, I also had a leak at the front of the valley when I only had one breather to a catch tank, this disappeared when I added the second one, and stopped using the tank.

mgbv8 · Post by **mgbv8** » Fri Oct 05, 2012 7:48 pm

Discopotatoes wrote:I now have both rocker covers at the front venting to atmosphere and a small filter on the breather at the back of the nearside rocker cover, but still get a leak under boost at the rear of the block from the Valley gasket I believe.
Do you think feeding the gasses from the rear of the rocker covers aswel to the turbo inlet would sort this?
I have had the valley off to try and cure the leak but to no avail!

The oil leak from the rear of the valley gasket is not unusual. If you dont seal the valley gasket properly it will seep out of the back on a N/A car. If you run boost you need BIG breathers to cope with blow by.
Can you show us a picture of your breather set up please?

For 20 psi of boost I would be looking at a breather from each rocker cover of at least 1" bore.

When you fit the valley gasket rubbers do you trim the wedge ends so they fit snug in the gap between head and block?

Do you use any sealant on these rubbers to gasket and engine?

Perry

Discopotatoes · Post by **Discopotatoes** » Fri Oct 05, 2012 8:17 pm

mgbv8 wrote:
Discopotatoes wrote:I now have both rocker covers at the front venting to atmosphere and a small filter on the breather at the back of the nearside rocker cover, but still get a leak under boost at the rear of the block from the Valley gasket I believe.
Do you think feeding the gasses from the rear of the rocker covers aswel to the turbo inlet would sort this?
I have had the valley off to try and cure the leak but to no avail!

The oil leak from the rear of the valley gasket is not unusual. If you dont seal the valley gasket properly it will seep out of the back on a N/A car. If you run boost you need BIG breathers to cope with blow by.
Can you show us a picture of your breather set up please?

For 20 psi of boost I would be looking at a breather from each rocker cover of at least 1" bore.

When you fit the valley gasket rubbers do you trim the wedge ends so they fit snug in the gap between head and block?

Do you use any sealant on these rubbers to gasket and engine?

Perry

I didn't trim the gaskets but did use sealant, I don't have a current picture and I'm away at work till next week, I have only used two flame traps with filters as breathers so I guess that the problem there I will vent the rear of the rocker and see if that helps

mgbv8 · Post by **mgbv8** » Fri Oct 05, 2012 8:45 pm

Venting the rear of the rocker cover wont make any difference. Both rocker covers are an air plenum. You can vent from the front middle or back. It doesnt matter where you vent the pressure from if the vents are not big enough.

If you have one large breather from one rocker cover that is big enough to get rid of the pressure that will do.

stevieturbo · Post by **stevieturbo** » Fri Oct 05, 2012 10:28 pm

Depends what you're trying to achieve really.

Some of the yanks will say a proper PCV system is by far the best.

ie. During vacuum conditions air is actually drawn through the crankcase and into the engine. That requires at least two connection points on the engine. Ideally far apart so that fresh air is actually drawn through the crankcase and all fumes etc inside are taken away and burnt. And this does make perfect sense, apart from the oily residue which will end up in the intake unless exceptionally good filters or oil/air separators are fitted.
Under non-vac conditions crankcase venting would be as per below and a check valve would close on one of the connection points to the engine.

For the simple folk like me...just adequate crankcase venting to atmosphere via a catch can, oil/air separator etc is the easiest to achieve.
The outlet of this could be fed into the inlet tract pre-turbo etc if you really wanted, but again you would need to decide how clean these emissions would be and whether you really want them being chucked through the turbo, intercooler etc

Or some of the old yanks setups would try and use exhaust gasses to carry out some form of extraction. Again this would still need good oil/air separation so raw oil doesnt simply get spewed out the exhaust.

So either way, adequate venting of the crankcase is essential, and most important is proper oil/air separation before it goes any further.
Most of the basic cans or crap you find on ebay are just that...crap.

Something like this actually looks pretty good.

http://www.horsepowerfreaks.com/partdet ... /E46/16619

Or here is an image of a schematic of an OEM M5 separator, which has some well thought out design.

OOPs, turned out bigger than expected lol

http://www.evo-host.co.uk/getimg/30068.jpg

Discopotatoes · Post by **Discopotatoes** » Sat Oct 06, 2012 4:55 am

Thanks for the info.
What I'm trying to achieve is just stop the oil leak, it's quite embarrassing after a spirited drive to pull up at traffic lights in a cloud of smoke as it drips onto the exhaust,
I think I'm going to start with removing the wire gauze from both flame traps first to see if that removes enough of the restriction, but this is going to remove the oil separation so might just end up clogging my filters! But worth a try I spose?
then failing that I will look into Stevie's idea venting to exhaust or turbo via a good catch can.

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Boost check valve in the pcv system

Boost check valve in the pcv system

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