LSx crankcase venting issues

So I've been having an issue with my LS1 swapped 944. This past season I was blowing oil out the exhaust on decel. Did wet/dry compression tests and they came back good, good compression and no difference between the two.

My pcv system was LS6 valley cover plumbed with valve cover vents going into a catch can, then the pcv valve, going into the intake.

My local CMC race engine builder told me to cap the valve cover vents, so I did. Now it's setup with the LS6 valley cover going directly into the catch can, then out to the pcv valve and into the intake manifold.

With this arrangement I blow the dipstick out of the tube, so the crankcase has positive pressure. I'm doing a leakdown test early this week to make sure I don't have a ring/piston issue.

Other people have suggested T'ing the two valve cover vents together and sending them to a second catch can that vents to atmosphere.

The motor runs great and makes the expected power (400rwhp), so I'd be surprised if I have a ring issue.

What do you all think?

A friend of mine was having these issues. He ended up doing what you suggested (vented catch can) and also putting some kind if spring retainer on the dipstick.

Did you check out LS1tech to see what other people are doing?

I just run them as GM designed 'em.

What Keith said. If you can't keep oil in it, it's detonating or has mechanical issues.

Not detonating. Spark plugs look good and AFR's on the wide band are spot on. Several other 944 LS swapped race car guys are suggesting the 2nd catch can.

LS1Tech guys are pointing at either a bad head gasket or possible rings/piston problem.

If the leakdown test is bad, obviously time to rebuild it. It was a motor I pulled out of a junkyard and now have 3 race seasons on, so it doesn't really owe me anything.

If it's good I guess I'll try the 2nd catch can.

Any other ideas?

if i read it right, your current setup has no path for fresh air to get into the engine with the PCV valve sucking thru the valley cover? if that's the case, then you need to add a pathway for air to get into the engine- the stock vents in the valve covers were designed for this purpose...

but since you are creating enough pressure to blow the dipstick out, i'd say you have some sort of an issue beyond that and it is time for a rebuild..

Sounds to me like you've got some kind of blowby issue too, but lets ignore that...your setup is workable, but unusual and not optimal. I think your catch can is going to collect extra oil unnecessarily since it's always exposed to the valley cover fumes.

So why did your engine builder tell you to cap the valve cover vents? The only good reason to do this is if they have a bad design which causes liquid oil to come out of them. And even then, getting some add-on baffle chambers to go near the vent ports (or modding the valve cover) is a better idea.

Here's what I'd suggest, assuming the LSX doesn't have any terrible design flaws associated with its crank vent system:

Attach the PCV as close as possible to the valley cover. Tee (or for a more tidy setup, "X") the valve cover vents with the PCV output. Connect this to one end of your catch can, and the other side to your intake. (suck-through is better than VTA for engine longevity and environmental friendliness, and with a good catch can is very nearly as good for intake cleanliness and keeping oil fumes out of the charge).

The PCV arrangement I have now is stock for the LS6's. The LS6 (and later LSx motors) don't even have valve cover vents.

The LS motor builder told me to cap them as he thought I was pulling too much oil up through everything, putting it into the intake and them blowing it out through the exhaust. I did have oil in my intake manifold, which seemed to prove his theory.

Nova, not sure what you mean by a pathway to get air into the motor....

OK that makes sense. You should look at adding baffles to the valve cover vents then (either externally or better yet internally), there's no way to fix this problem without doing that. You need to pull more air out of the engine, in a suck-through configuration the pressure in the crankcase should be lower than the atmosphere. When you blocked off the valve cover vents you stopped liquid oil getting into the intake, but you also reduced the amount of air getting sucked out of the engine, and now it's not enough to keep blowby from building pressure.

docwyte wrote: The PCV arrangement I have now is stock for the LS6's. The LS6 (and later LSx motors) don't even have valve cover vents. The LS motor builder told me to cap them as he thought I was pulling too much oil up through everything, putting it into the intake and them blowing it out through the exhaust. I did have oil in my intake manifold, which seemed to prove his theory. Nova, not sure what you mean by a pathway to get air into the motor....

the pcv valve controls the airflow thru the crankcase- in order to get "flow", you need a path for the air to get in.. in old school small blocks made starting in 1968 or so on, they put a breather on one valve cover to let air into the crankcase and the pcv valve on the other valve cover to suck it out and put it into the intake manifold- if you take the breather out and just plug the hole, there is no "flow" thru the crankcase to carry away the bad fumes. also, when you go to a low vacuum situation- like, say wide open throttle- the pcv valve closes and if there isn't another airflow path, any pressure in the crankcase will try to find the easiest way out- which can mean anything from blown oil pan gaskets or crank end seals to excessive oil consumption from the pressure pushing crankcase gasses up past the rings on the pistons.

LS3s definitely have PCV setups, but it's done a bit differently. It's actually a metered orifice IIRC, and the plumbing is pretty low-key - but it's there.

Keith, I meant the later LSx's don't have valve cover vents. They have PCV systems like the one I'm currently using, it's integral to the valley cover on the later cars with no external PCV valve.

Mine has the earlier style LS6 valley cover vent which uses an external PCV valve.

OK Nova, I think I follow you. So I should tie the valve cover vents together and run them to another catch can that vents to atmosphere and I should be ok then if I'm following you, right?

The problem I see with what novaderrik suggested is that oil will still spill out of your valve cover vents, it'll just collect in the catch can rather than being burned in the engine, it'll fill up pretty quickly that way. Other than that it'll work.

What oil pan do you run and how much oil do you run in it? ...just curious.

I've built a few systems and have had luck simply taking the valve covers AND valley, connecting it to the can inlet/dump and then take the top can outlet to the intake. Theoredically high rpm/load/G-force is making windage and some splish-splash that the can will catch. If you FILL UP THE CAN with something similar, then you most likely have a mechanical problem. I'd consider a good leakdown test right off track, hot temp!

If you are using a production oil pan then just get a catch can with a breather vent and good baffles and plumb the catch can drain to a plug in the stock oil level sensor location. Tie the valve covers and valley pan in and don't worry about the pcv. The can will catch the oil vapors and they will drain back in to the pan.

Custom pan. No other way to fit an LS into a 944, it's from Texas Speed and Performance, supposed to be baffled. I run a bit below full, so around 8 quarts when you consider my oil cooler and lines.

Catch can wasn't really filling up last season, I was blowing all the oil out the exhaust. I have an Elite Engineering catch can.

Well leakdown test confirmed my suspicions. I have worn rings, numbers were 10-15% at best.

Time to yank the motor and do a rebuild. I'll add a set of ported and decked LS6 heads while I'm at it, because race car and moar powah!

I love how any given failure can be used as justification to upgrade something. Carry on!

Armitage wrote: I love how any given failure can be used as justification to upgrade something. Carry on!

why take things apart twice? it just makes good financial sense, and it also makes sense from the time management perspective..

Positive Crankcase Venting. The purpose of the PCV system is to create a vacuum in the crankcase in order to remove fumes. It serves no other purpose. If there is no vacuum there is something wrong.

novaderrik wrote:

Armitage wrote: I love how any given failure can be used as justification to upgrade something. Carry on!

why take things apart twice? it just makes good financial sense, and it also makes sense from the time management perspective..

There was no sarcasm in my post. I do this all the time myself and suspect most everyone else here does as well ;)

LOL. I'm definitely guilty of the "While I'm in there..." syndrome. At this point I'm also considering selling my current long block and buying a built 383. If I can get $1000-1500 for my long block with cam, the money gap between having my motor rebuilt and purchasing the 243 heads will be pretty small...

iceracer wrote: Positive Crankcase Venting. The purpose of the PCV system is to create a vacuum in the crankcase in order to remove fumes. It serves no other purpose. If there is no vacuum there is something wrong.

I am under the impression that the crank spinning and pistons moving create a positive pressure. The PCV system is there to relieve that pressure. That does not necessarily mean there is a vacuum. I would actually think that there will not be a vacuum. The best you could hope for would be atmospheric pressure.

If the PCV system created a vacuum, wouldn't it start sucking oil out of the crankcase?

Rob R.