jad568

I just picked up an 07 Z06 Twin Turbo a couple of weeks ago and I'm trying to learn more about oil return issues. It is an "HP Performance" kit (turbos in front fender area) with twin 57mm's.

If the car is at idle for more than a few minutes you will start to smell a burning oil smell. From what I have heard this may be due to the oil not returning from the turbos to the dry sump at idle. As soon as the RPM's are raised the issue goes away immediately. So I'm wondering if someone else has seen or heard of this issue and what was done to resolve it.

Thanks,

-John

0INTMD8

Are the turbos ball bearing or journal bearing?

Do they gravity drain into the pan or is there a scavenge pump that returns the oil to the reservoir?

Drewstein

No gravity drain with dry sump my man.

OP, you need to check how the oil is scavenged from the turbos. If RPMs are affecting it then it could be a mechanical scavenge setup whereas mine is an electronic setup. Check that and get back to us.

jad568

I'm checking with HP Performance and I will crawl under the car tonight to see how it is setup/plumbed.

Drewstein

They'll be able to tell you how it's scavenged and then you can test if it's pulling enough at idle.

jad568

So after talking with HP Performance and looking under the car, it appears that they are indeed gravity return and have journal bearings. They are suppled by a "T" fitting that gets installed at the oil pressure sensor and simply returns to a fitting that has been tapped at the lower section of the dry sump.

I'm wondering if the crankcase pressure is too high at idle for the oil to return into the sump since the oil pressure is lower at idle as well.

Drewstein

Well now I'm really confused as I understand the turbos would have to sit above the top of the oil level in the sump to be properly gravity drained. I can't imagine HP's setup having turbos above the motor like the C5 PTK systems?

Sorry I couldn't be of better help. There are some great vendors like IPS that can better assist I think.

jad568

Yeah they do sit up above the sump in the upper rear wheel well area. May need to check the crank case pressure at idle. Not sure if there is a crank case relief valve...Need to do some more digging to find out how it is regulated.

Andrew M

A few simple things you can check before getting deep into it.

1) Check the return lines on the turbo's, make sure they are always going downhill all the way to the fitting in the oil pan.

2) Find out if there are any restrictions in the oil feed, it may be a case of just too much oil getting into the turbo's.

3) Does the car actually start to burn oil out the exhaust if it sits long enough? Or are you basing all of this on oil smell? If you have oil backing up in your return line it will start to come out the back seal in the center section into the exhaust/intake of the turbo.

jad568

The return line routing looked good from the turbos down to the sump. As for the supply lines, I didn't notice any inline restrictors, but I will need to take a closer look to verify.

As for the burning oil, yes I start to get some smoke out of the rear pipes along with the burning oil smell. Not a ton of smoke, but its there. I does seem like the oil is backing up in the turbos and getting in to the exhaust.

0INTMD8

While maybe not the best option they could be gravity draining to the oil pan where the scavenge side of the pump would return it to the reservoir my man

(and it appears that's how it is set up on this car)


I doubt the problem is crankcase pressure related. How is the PCV system routed? What size hose is used for the turbo drains?

You may need to restrict the oil feed at the turbos if they are seeing too much pressure. What brand turbo?

jad568

Yep, that is how it is configured. The return line looks to be about 5/8" OD, so ID may be 7/16" or 1/2". Seems like plenty of size for this amount of oil. The reason I was thinking about crankcase press is this problem only occurs at idle, when the oil supply pressure is only at like 20-25 PSI vs around 50 PSI at cruising RPM's.

Seems like if the turbos were getting too much oil the problem would be worse at higher RPM's unless the turbos help the oil to return the faster they spin, just not sure. I need to look closer at the PCV system. I did look at the passenger side valve cover and there is a plastic plug on that valve cover, so no breather. I will look around for a PCV schematic.

Drewstein

I'll try to elaborate on Intmd8's post to see if I can clarify.

The oil leaving the turbos is going to the "pan" which is picked up by the motor driven oil pump. If too much oil is flowing through the turbos at idle (unrestricted), it will backup the drain line and sit in the turbos. If the oil feed were restricted a little more, then just the right amount will pass through at idle allowing it to be scavenged from the pan. As you pickup RPMs, the pan is emptied at a better pace which is why you don't have the problem then.

The "pan" is so small I couldn't imagine gravity draining to it, but Intmd8 is on to something there for ya.

0INTMD8

That's what's odd about the LS7. Most dry sump pans have a very small area in the pan for the pickup which makes for efficient scavenging but the internal dimensions of the LS7 pan are actually pretty big, similar to a wet sump pan.

Maybe take a picture of where the drains are located in the pan. If at the bottom than I could see it getting backed up, but if they are towards the top the oil level in the pan should never get up that high.

jad568

Got it, now I understand. That makes good sense. I will get a pick of the entry point of the return lines over the weekend. Very interesting...

cwylie

You ever resolve this problem?