acroy

That was scary: quick WOT blast through 4th, big cloud of smoke in & behind car.
Passenger side of engine, underside of hood etc all oily. Luckily did not catch fire!
I think i know why, but a little gunshy now. please review & provide comments! Thanks in advance.

contributing factors:
- this is a LS2 based 427, built some time ago by MTI. Engine was built a bit loose, it does consume some oil, around 1qt every 500-1000 miles depending on use
- compression test etc are fine. Pulls consistent vacuum @ idle. Spark plugs look great but for slight oil residue on threads (not on or near electrodes). No indication of engine issue
- Valve cover vents are capped (no PCV system)
- Single vacuum line from valley cover to AMW catch can to intake manifold

When I bought the car I swapped out the fancy vented oil cap for stock. I was concerned it could let unfiltered or poorly-filtered air into the engine.
I think this set me up for seriously under-vented engine, and it finally spewed.
I put the fancy vented oil cap back on, though I do want to test to ensure it can only flow OUT not IN.

couple pics for visuals:

Robrote

Was the dipsticked bolted to the head? If not, why not. Was it the stick that blew out of the tube? You probably need a catch can.

3sACROWD

Your vented oil cap shouldn't be an issue . Unmetered air is a concern on the intake / combustion side.

Since you don't have a PCV and you put an unvented cap on, your engine couldn't relieve the pressure on the bottom end and pushed to oil dipstick out. Sounds like your engine checks out OK since the event. Keep the vented cap on.

aaronc7

I went thru similar troubles after getting a new built (and looser) motor.

It's logical to assume that a built motor and more cubes etc will increase blowby under load.

By capping the valve cover vents you effectively halved the venting capacity of the engine.

If you put that oil cap back on, it will definitely suck air in at idle and cruise. The vacuum from the intake manifold will pull air/vapors from the valley cover/crankcase. It will also be unmetered air, and will throw off fuel trims at idle mostly.

The purpose of the valve cover to TB hose is to provide clean air into the engine and provide additional venting capacity under the load. This is also "metered" air and won't affect fuel trims.

First things first, I would re attach the valve cover hose(s) and a PCV valve between the valley cover and intake manifold (unless it's an 04+ valley cover that has the fixed orifice restrictor internally).

From there if you want to add additional venting, you can go from there. The oil cap breather is definitely an option, but it will still affect fuel trims a bit at idle (not ideal, but not a huge deal either). They make a breather filter that replaces the whole oil cap and has a check ball integrated to only let air out....not in.

Please correct me if I have any details wrong about your current setup... that is how I interpreted your post. Pics of everything would be great too to be certain we're on the same page.

acroy

thanks for reading & the suggestions.
I was reading your thread yesterday..... head spinning after a bit what setup did you settle on?
I *think* the cap I have has a check valve in it - will rig up a tester for it.

aaronc7

My issues were a combination of built motor with slightly elevated blowby levels (as expected), coupled with road course use.

I think the bigger issue I had was oil control.... the valve covers would fill up oil from extended high rpm use/high G scenarios. Then I would go into a corner (high G), the oil would pool up around a vent...and then I would get off the gas... engine vacuum would literally suck that pooled up oil out and fill up my catch can quickly. I probably run a higher volume oil pump than I need as well..which only makes this issue worse.

I ended up getting a -10AN fitting on each valve cover, at the highest point, roughly in the middle of valve cover (to avoid pooling under accel or braking). I also routed the valve cover vents back into the air intake (not intake manifold) so they never saw vacuum. With this setup, after a few 1000s miles of street driving my can was virtually bone dry.

Anyways, that setup is obviously a little more involved... I think step 1 for you is to return to stock pcv functionality. I would run a single catch can between the valley cover and intake mani like you have (and add PCV valve if you don't have 04+ valley cover). Open the valve cover vent(s) back up. Ideally back into air intake, but vent to atmosphere is fine too... it will just affect idle fuel trims and might smell a little after hard driving. In my experience the valley cover is the side you want the catch can on and where most of the oily vapors will come from.

acroy

Thanks, very valuable insight.
I'll look into implementing your suggestions.
I prefer to have minimal unmetered air, doubly as the car has an lightweight flywheel + light-switch clutch, so idle/just off idle tuning is extremely important for driveability.

kh400

Blowby!!!!!

gimp

Why don't you have a PCV system anymore?

ZigZag

CFM Central Florida Motorsports has them for sale. I got the one with the check valve for my LS2 and it cured my crankcase overpressuring. It may be just what you need.

smuggler85

Interesting, aaronc7. I'm curious about feeding a valve cover vent into the air intake tube. Wouldn't this create a suction effect and tend to pull oil vapor from the top end? I would think this would also introduce an oil film on the MAF and TB wires, creating additional issues.

aaronc7

In 99% of engine operation, the intake manifold will be in vacuum, ballpark -10 to -5 psi. The suction effect in the air intake tract will be much less (I haven't done my own measurements, but only a fraction of a psi, so at least 1 order of magnitude difference).

So in 99% of engine operation, clean air will be flowing from that air intake tube to valve covers, circulating clean air thru the crankcase and will be sucked back into the intake manifold via the vacuum condition it is under. Some of the air at this point will contain oil vapors etc unless you have a catch can.

Then under wide open throttle, when blowby is highest, the valve cover vent serves as a crankcase ventilation option along with the intake manifold (but the pcv valve, catch can etc all provide a decent flow restriction). At WOT, air flow will increase in the intake and also increase the suction effect on the valve covers slightly...but still not even 1 psi or any 'significant' amount.

Since WOT operation is really not a frequent thing, the amount of oil vapors you can expect to come out that path is very minimal. Unless of course you have a hurt motor with excessive blowby or this is a roadcourse car where it indeed seems WOT very often. Most at this point would add a catch can or just vent to atmosphere for convenience.

I think MAF contamination is a concern...but normal street car I don't think it's really going to be a factor. Ideally you could just put the hose behind the MAF....but looks like in your case that is not really an option. With a stock LS1 throttle body this is accomplished by the nipple on the throttle body-- it comes in right before the throttle blade.

acroy

PO had the car built this way. The build was mostly simple & robust though not suitable for a track with corners... Show and go in a straight line.

Josephu

You say that your motor was built a bit loose. A quart of oil in 700 miles is too loose for me. The only true way to check the condition of your motor is to do a leak down check on it. A block that was honed with a deck plate,, and the correct stone procedure,, correct ring package for the hone,.. correct cleaning procedure before the assembly process,,,,will not use a quart of oil in 700 miles.. To blow the dipstick out means that there was a lot of blowby.. If it didnt go out the dipstick, it would have gone out your crankshaft seals. Do a leak down test and report back your results. 2% to 5% is good....10%.. fwell, you can live with it...20% is getting pretty bad. Anything over that, and you had better have a big coffee can for a catch can. Put the vented cap back on and run her through the gears. If it covers your valve cover with oil,, then your rings are probably toast,, and not sealing. Or some broken,,,wore out ring lands on the piston. In my opinion, it would be time for a teardown and inspection by a qualified engine shop. And a rebuild......the right way.

acroy

Leak down is on the to-do list. There are some great shops in this area and if it comes out low I'll have one of them do a refresh.
Regular compression test was fine, I forget the # but all within a couple PSI.
I ran the vented cap until just recently, plenty of WOT runs, zero oil on the valve cover.

aaronc7

I thought the quart in 700 miles was excessive too....but might have been some weird stuff going on with the pcv system. Get that sorted, then take another look into things. How much oil has your can between valley cover and intake mani been catching?

acroy

Minimal, like an ounce in 3k miles.
It went through about a quart every 500 miles on a 2200 mile road trip from Seattle home to TX when i bought it June '18. Car has 4.1 gears so it's spinning around 2200rpm @ cruise iirc. It had no PCV system at this time (vented cap + catch can only). This was 5W30 oil.

I changed it to M1 0W40 and it has seen only city miles since. I rev it through the gears pretty good all the time, for the fun of it. Oil consumption has actually decreased to the current 1qt per 800-1000 miles. No oily residue on the exhaust or rear of the car, just sooty, it burns the oil cleanly. Plugs look great though threads are oily. The car sat a lot with POs (maybe 8k on the build over 12, 13 years) and I have a suspicion the valve stem seals could use replacing.

Leakdown test will be interesting, I've just not prioritized it, as it runs so well and the 'shade-tree mechanic' tests indicate a healthy engine.

Cutlassmaster

If plugs dont look all oil burned then you could be sucking it past exhaust valve seals. I have a 402 and they guy that did the heads must have used the wrong seals. I used 6 qts in 3,300 mile trip. I replaced all the valve seals and now it doesn't use any. My plugs looked great and did not look like oil was burning at all.

acroy

Update
- For a few days I re-installed the vented oil cap back (it has no check valve and breathes very easily in & out). off-idle driveability took a crap... all that unmetered air had a large impact. I had been 'driving around' the issue previously.
- I then installed the standard oil cap & rigged a vent to atmosphere from the passenger side valve cover with a generic PCV valve. Driveability came back. The generic PCV check valve does not seal 100%. It leaks a little just with the 'mouth vacuum' test.... un-metered, unfiltered air.
- I've ordered parts to install permanent venting, with PCV inline, from both valve covers into the intake tract. It will be installed after the filter & MAF; before the throttle body.

the car will then have the setup you recommended.

a couple notes:
- the engine does have the later model valley cover with orfice
- catch can (between valley cover & intake mani) has no check valve. Blowing through it, it does have significant flow restriction in both directions

I also received a leakdown tester but not tried it out yet...

aaronc7

If you have the fixed orifice '04 valley cover you don't need or want a pcv valve anywhere on the car. On a NA car I don't really think a pcv valve really does much other than limit/restrict vacuum on the crankcase-- same function that the small orifice 04 valley cover does. On a boosted car, it would close under boost and prevent the crankcase from pressurizing too.

The valvecover to air intake tract you just want simple hose.

Here's my setup.... originally did it for the track use as described above, but works great with boost too.

Catch can, pcv valve built into lower port between can and intake mani

Attachment 48349110

Valve cover vents, -10AN, both routed to intake tract. I don't have a MAF, so I could easily vent to air, but I wanted to keep fumes down and not have any oily spray potential in the engine bay.







Attachment 48349114