You're making assumptions here (par, indeed). I never said there was anything wrong with the stock valves. I never said anything about anything, other than the fact that the LS7 can generate a significantly larger thermal load compared to the LS6.

 

FRDnemisis, did your LS7 blow? What are your guide specs? Can you please post the sheet?

Mine for example did not blow thus far, and I know my guides were in spec because I pulled my heads and I had them measured. The problem here, is you have a huge group running around with theories about guide wear, and what maybe 5 of us have posted up actual accurate measurements, not some thumb in the air method of wiggling valves.

All I am trying to say is there is a certain amount of use you can get out of something, certain types of usage accelerate the life cycle, although it is impossible to quantify each instance exactly. One needs to be realistic in what to expect. Tracking is a huge variable, but I agree, I have seen enough non tracked low mileage cars fail to still wonder why they failed. However, few are providing solid data, only pouring more gasoline on the theory fires. I provided my data, hopefully we get more data and less gasoline. I'm not simply trying to extinguish the fire. Go ahead and pull your heads to help others out too, it will help everyone.

 

Yes it can but that isn't the total picture. The combustion temperature is the same for each engine, the efficiencies are about the same and an LS7 may heat up faster but it will reach a ceiling temp based on the combustion temp and won't go any higher. The LS6 will also reach that same ceiling temp although it may take a lap or two longer to do so. The LS6 has smaller everything and probably puts as much heat load per unit of area on the components as the LS7 does. I don't know how hot those internal engine pieces get but after a 25 minute track session I bet they are all running right around the same temp whether in an LS6 or LS7. Add on top of that the LS6 will be operating nearer its maximum manifold pressure longer than the LS7 since the laws of physics limit the speed at which the cars can get around certain portions of the track no matter how much power they have. If both cars are equally suspended (common) and power through a 1300 ft long section of curves at the same max speed (less than 100) they are both expending the same HP. The LS7 will not be running as hard as the LS6 to do that. Given that some drivers in both sets of cars run the curves in third gear the LS7 will actually be loafing compared to the LS6. A lot of variables to take into account and based on 20 years of doing this stuff I think the LS7 works harder on the long straights where it can use its extra power but the LS6 works harder in the other areas. The net is during a session they are run equally as hard with the LS6 having a decided edge in durability. We just don't see them dropping valves, they just seem to go on and on and on.

Bill

 

My car is PARKED as of yesterday and will not be driven until I can derive a course of action from whatever statement is waiting to be made by GM.

But regardless, my heads will be coming off the car sir, I will guarantee you that. But I will not pull them until I have a replacement in my hands to keep from having an open motor exposed to the climate during the wet winter months here in Charleston.

I may pull my heads to find out; WOW, I'm okay afterall OR I may quite easily find "WOW, I was on borrowed time!" I have a sneaking suspicion it will be the latter because this summer I have noticed what "I think" is some real valve noise between 1,500-2,500 RPM. Past 2,500 I cannot hear the motor over the exhaust because the butterflies start opening up.

If they are indeed fine, I will sell them to help recoup the new set of whatever I purchase (may be GMPP LSX LS7 heads if the problem did in fact, NOT follow over to them).

I mean NO disrespect, that is not my intent and I understand what you are trying to do; but when I read your post that I multi-quoted, it just seemed that your statement was trying to minimalize what was transpiring. I just think many, many of us are a bit on edge right now.

Respectfully,
Jeff

 

The guy on here that had 24,000 track miles and dropped a valve sent me his broken valve stem as well as a couple of the non broken exhaust valves.

The exhaust valve which dropped showed virtually no signs of guide wear (i'm sure some of you will say "well how do you know that, you weren't there!!??!?!?!") no galling, and a very crisp carbon buildup line. Nothing like that of mine which were pulled at 25k of spirited street driving. To make things even more interesting, the walls on the valve stem were almost perfectly even. Unfortunately the area where had broken was pretty beat up and i was unable to definitively find crack propagation on a grain boundary.

This to me looks like a classic fatigue failure, i deal with fatigue, inlcusion size, welding and exotic materials on a daily basis. I think a lot of the data we have is an amalgam of variables all contributing to one thing, weld line fatigue failure. Guides out of concentricity with the head will help to wear them, causing pinpoint stress and higher deflection. Excessive heat can cause thermal expansion and galling of the guide allowing more oil through and a domino effect starts with the coking/galling which eventually ends in higher stress and accelerated fatigue.

just my 2 pennies...eager to hear what GM has to say......

 

Well said .

 

excellent post.

 

I stayed with stock valves when my heads were redone as well.

 

Guys, don't hold your breathe on an announcement. Do this. Take 900 and divide it by 2. That is roughly how many corvettes are selling each month, and assuming 50% are LS7s between Z's and 427 Verts, which we know is a generous assumption. Now, divide 450 by 240,000. That is the percent of sales the LS7 generates in a given month (roughly) currently. I haven't done the math, but that has to be like a fraction of 1%.

Now, put yourself in an OEM's shoes and see if you think you'd spend a bunch of time and money to quell paranoia on an internet forum for a model about to go into sell down to make way for the new gen (irrespective of whether you think there is an issue or not)? If there was an official NHTSA investigation, then yes there would be. However, I am fairly certain you will hear nothing but your own breathe. If there was an issue with a Silverado motor affecting roughly 50,000 per month, then yes you're more likely to invest a little time and money to relieve tension or resolve an issue. I just don't see it here.

 

Thanks very much for your report.

So if you were taking your heads off would you replace the stock exhaust valves with SS or not ?????


DH

 

The biggest factor may be "What are we going to say?" "We are damned if we do and damned if we don't."

Bill

 

Even if combustion temp is the same - I'll stipulate to that, since neither of us know for sure - the combustion chamber can be exposed to that temperature for a longer time in the LS7, because the redline is 10% higher. Therefore, more heat is transferred into the surfaces of the combustion chamber. Consider a pot of boiling water that you dip your hand in for a second at a time - even though the water is the same 212 degrees, would you rather dip your hand in it 10 times per second or 11 (it's academic, but you get the point I hope).

The valve is larger in the LS7, so it's going to absorb more heat - but the stem area is the same in both engines, so the same guide area has to deal with a larger number of BTUs/kCal/Joules/whatever unit you like.

 

I think it's to that point right now. There has never been this much collective tension/anger/frustration and confusion (all at once) in all the years since this started happening, until right now. It's a volcano on the brink. Being quiet just might not be in GM's best interest if for nothing more than the negative publicity. It is past the point of just people who had failures being pissed-off. It now has people that it hasn't happened to now very wary and un-able to enjoy their car without that constant worry "is it going to happen today?" Do they think those people are going to buy newer vettes if this is the kind of loyalty support they are going to get? I'll be the first to admit, if I had a C1 thru C6 LS3 car, these failures wouldn't bother me, but they would damn sure keep me from buying an LS7 car, believe that and I'm probably not in the minority. Who buys a perceived troubled LS7 car for 50-100 thousand dollars?

Wouldn't it be easier to say:
"Hey guys, We've fixed the problem, we will replace the known defective cylinder heads upon exchange." If you are under warranty, come on in and let the dealership fix your car 100% warranty work (GM comes out cheaper replacing cylinder heads vs. destroyed engines).

If you are out of warranty, bring your cylinder heads (off of the car) and we will exchange them; the labor is on you." At that point you would have the proudest life long patrons in the world bar-none and poof problem gone. I would be more than happy to pay the expense to have someone swap my cylinder heads just to have the piece of mind and go back to oblivously enjoying the baddest Naturally Aspirated Corvette ever produced!

That's just my fantasy world but it makes sense to me.

 

Their competitors, Porsche, Ford, Mercedes, Dodge, BMW, would descend upon them like vultures, and have a field day with this matter were they to do that.

Automobile companies are reluctant to admit blunders even when they cost human lives. It is doubtful that GM is going to admit one here affecting a small percentage out of 27,000 cars.

They don't care about "customer loyalty" amongst Z06 owners. They don't care about pissing off Z06 owners. Why do you think they built the grand sport?

 

well said

 

this is what i found to be the case in the heads from 505z06 ....guides were in spec...

 

Anyone remember that 1999 Ford Cobra fiasco where Ford was pretty much forced to admit that those cars weren't making the power advertised.

That was a public relations NIGHTMARE for Ford and team Mustang and SVT. And it damaged the value of those cars beyond any fix supplied by Ford.

This would be at least that bad and probably worse. A whole lot worse, especially with 427 convertibles rolling off the trucks.

 

again..and this was why they didn't make a 2000 cobra..and this was just a power issue and motors were not popping ..once ford came out with the 03 cobra things got back to normal for the cobra..and it has done well since

 

As a potential newer Z06 customer, I agree, with the above and that would help me have confidence in driving it, furthermore on a mountain road (which is my intention) without leaving my wife a widow

 

Not me... I was actively looking for a 2008-09 Z06, had made offers on a couple at dealerships, and was intending to look at another private party offering just a few days ago when I threw in the towel and got out of the market. I don't have time to fiddle with heads being pulled and rebuilt, and I don't even have the time to fiddle with a blown engine under warranty. I do have occasional time to simply drive and enjoy the car, but it was increasingly looking like that was not going to be an option (at least the enjoyment part).

So, I'll leave my cash in the bank for the next few months, or the next 14 months, and see how this eventually settles out. Odds are that when I to buy one (it would be my 7th Vette over the course of my lifetime) I'll get one out of warranty, at the low end of the price range, and send it right off for the heads to be pulled... unless good news develops about the guide issue not being widespread, which I tend to doubt (despite occasional signs to that effect).

At this point all I can say is that it's too bad that Chevy didn't let MerCruiser build the engine for this one, as they did for my last Vette