A427MAN

I sent this email to Janet:

Hey Janet, I just read a post that said you guys blew the motor in the new Z06.

Is that true? If so, what happened? ...what are the details? ...was it valve spring related?

Here's what Janet had to say:

Ron, We do not know what happened to the Spring Mountain Z06. It was making a noise and we took it into the dealer. GM replaced the engine, but we were delayed getting the Z06 back because some small part (not engine part) was missing.

The dealer did not take the engine apart so we do not know what caused the noise. We cannot say it was a blown engine. GM wants the engine back intact so that they can research the problem.

Where did you see the info about a blown engine?

Janet Curran

Verrückt

Jim, I'm glad we can discuss this in a civil way.



I agree that it is unlikely the rings would have a gap issue. However, many other factors can influence blowby and oil consumption.

Ring tension, ring barrel shape, ring sideface roughness, piston groove shape, block bore distortion, honing pattern, ring radial contact pressure and more can all have an influence.

GM is only as good as its suppliers. We are only talking about piston rings here. If you add up all of the possible things that can go wrong in the entire engine assembly, GM would be inspecting things for 3 weeks before they could even start building the engine. I'm sure they put some level of trust into their suppliers and measure some attributes in batches.

Now I don't know exactly what GM measures before putting the engine together. It's likely the critical dimensions.

Working on the supplier side, I know it they checked everything...it would be unbelieveable tedious.

allanlaw

Thanks for that vote of confidence, Jim. The oil level in this car has been checked in manner specified in the owner's manual (and your various postings) since day one. This includes checking it at the track after each session - it was not overfilled, end of story. However, what I'm thinking is that maybe the oil should be lower on the grid range on the dipstick if it is going to be run hard (the opposite of non-Z thinking). You can be sure I'll be watching this as time progresses.

allanlaw

I think this is the likely explanation, and something with the design of the dry sump system makes it particularly likely to happen in the Z. Some day when the service manual is available we can see some details.

Racer X

I am surprised that an engine with a dry sump system would generate excess positive crankcase pressure. I would have thought, if anything it would be slightly negative. The sump pump should always remove oil from the crankcase faster than it goes in, otherwise you will eventually fill the crankcase with oil. So it by design has to be sucking some air out of the crankcase.

So if not negative pressure in the crankcase, at least lower than a wet sump engine. So we should this as a much bigger problem in the LS6 engines as an example. I don't remember this being a problem in that engine.

cbgpe

The misting problem increases with RPM that is why we see less of it with the ls2 see my prior post on this problem...

Cobra4B

Wait... so the intake manifold is designed to accumulate condensed oil mist then send it back to the pan? Is this the ccas on an LS6 motor too?

allanlaw

Here is the official explanation:

"Oil is generating through the upper intake plenum and blowing down through the air cleaner assembly. Called technical and spoke with ++. Engineers state that this is a normal condition and caused by higher engine pressure vaporizing the oil. This system DOES NOT unse a PCV valve. New design crankcase ventilation hoses/pipes are used instead. This oil CAN BE CLEANED DURING NORMAL SERVICE INTERVALS. Note: This condition is most noticeable on manual transmissions due to downshifting and higher RPM capabilities."

That last sentence leads me to believe that the Z is not the only car with this system.

A427MAN

"This oil CAN BE CLEANED DURING NORMAL SERVICE INTERVALS."

Allan, I don't get this - what does that mean, exactly?

StickShiftCorvette

Just two points.

High temperatures reduce oil pressure.

Oil Pressure is limited by a relief valve in the oil pump - it does not run any higher at high speeds unless the system is so undersized that it only reaches the relief pressure at high speeds or when it is cold and engine speed is high.

cbgpe

YES

allanlaw

I haven't a clue - just quoting (although I added the caps for emphasis) from the tech's report.

allanlaw

Is this just general information, or do you have specific information that this is how the LS7 operates? Watching my oil pressure guage leads me to believe that the pressure does go up when the revs are particularly high, and it drops at idle. Is this incorrect?

VNAMVET

[QUOTE=Verrückt]Jim, I'm glad we can discuss this in a civil way.[QUOTE]


You DO know who you are speaking with, don't you.................I do.

cbgpe

The air/ oil that is pumped out of the crankcase is seperated.... the air (loaded with un burned HC & blow by) has to go some where ...in these days of strict emissions it will be put into the intake. No matter how good the seperator some oil will be entrained ... exceed the storage capacity of the manifold and it will leak out.
IF you study current intakes you will find a reservoir (sump) to store this oil and a drain back into the crank case.

JMB

I wouldn't be too quick to make this statement. You probably didn't see my post here http://www.ls1tech.com/forums/showthread.php?t=439847

Since my motor only has 20 minutes running time at the Wixom Faciltiy are you suggesting that it was overfilled at the Factory by the engine dyno operator....I don't think so.

I also spoke to the dealer where I purchased the motor and they have observed the same oil condition on a motor which they pulled the TB on.

I believe this is a lot bigger issue than GM wants to admit to.

For any "doubting Thomases" out there...I suggest you pull off your LS7 Throttle Body and take a peek at your intake manifold for yourself! I'll bet you see a puddle of oil!

A427MAN

Hey JMB, ...just curious, how much was the LS7 crate motor?

NORTY

OK,so the oil puking into the intake tract was from being "overfull." There is a lot of reciprocating going on in the higher RPM's. This air is swirling around at a high velocity. It picks up oil when moving around fast. If the oil is "high",then it's easier for the air to pick up the oil. This can be fixed 2 ways- either lower the oil level (and risk starvation.) or create a vacuum inside the block. If there is a vacuum inside the block,then there will be an increase in horsepower also as the underside of the pistons don't have to push the air around. We've used this technique on racing engines for years. It is good for about 6-7 HP on the dyno. Mostly topend power though...

Mako7

WOW! A lot of stuff to wade through in this thread. So Allan, you had a throttle body failure AND the car barfed up oil? AAAARRRGGGG!!!

My thoughts on the matter:

1. It has nothing to do with piston rings.

2. The best thing for us all would be if the oil was inadvertently overfilled. I understand from Allan that this is not likely.

3. The next best alternative is that there is something specifically wrong with Allan's Z (which can of course be fixed).

4. If none of the above applies, then all of us who enjoy a HPDE WILL enter the MOD zone!!

A. It is highly common for the Vipers and Vettes at the track to have this problem.

B. To resolve the matter on Vipers and C5s, breather tubes and catch cans were installed. This SOLVED the problem.

C. Case in point: My buddy and I were at California Speedway with our C5R Block 427 C5Zs a few years ago. His car was more race car than mine and he was running a bit harder. After one HPDE session we pulled into the garage. A few minutes later he had a lake of oil below the front of his car. We were amazed and confused.

He then took his Z to the race shop and they found that one of the breathers on one side of the engine was clogged by design; the one on the other side of the motor was fine. They then corrected the breather tube on the first side (which I think required them to drill the heads and install a tube) AND installed oil catch cans on each side of the motor. Presto, chango, no more oil burping. I have no idea how this fix is affected by the dry sump system.

My suggestions are to: (i) work with the Dealer until that will not work anymore; and (ii) then call Tillack & Company in Redondo Beach, CA (tell them I sent you and so did Perk Burnett).

5. One very interesting issue here is WHY LG is NOT having such problems. We KNOW he runs his Z much harder than we will. The first thing I think of is his upgraded Radiator and Oil Cooler. {We had those in our c5Z 427s also}

ANY IDEAS LOU?

Keep us posted!

Cobra4B

I know my buddies race viper will burp oil and blow blue smoke when he purposly overfills it a bit at the track. As the session goes on it'll eat what it wants then stop.

I find it hard to believe that GM's engineers would miss something large. They learned their lesson with the 2001 Z06 and to extensive testing and tear down on these motors. I doubt it's a big issue and I hope you get it resolved to your liking