LawrenceFromTorrance

Your comments have merit but what bothers me is that for every LS7 that makes it to 100K without valve problems there are ten that don't. I also think that the problem is a geometry problem but that it's in every LS7 just lurking there .... waiting

davenp

hy·per·bo·le
/hīˈpərbəlē/

noun: hyperbole; plural noun: hyperboles
exaggerated statements or claims not meant to be taken literally.

sen·sa·tion·al·ism
/senˈsāSHənlˌizəm/

noun: sensationalism

1. (especially in journalism) the use of exciting or shocking stories or language at the expense of accuracy, in order to provoke public interest or excitement.

LawrenceFromTorrance

Yah, I know I did not back up my claim with a list but if I had the time I don't think I would have a problem of finding a ratio close to 10 to 1 just looking on this forum. I only remember 1 or 2 LS7s with 100K that did not have/show valve problems. I could also say that your doing the same thing because your not publishing facts to back up your claim that I'm embellishing the situation.
If anybody has facts to put forth on this LS7 problem I've not seen it. Only opinions, sorry if my opinion struck a cord for you

LawrenceFromTorrance

Actually, here 36 to 4 (9 to 1) using 60K not 100K. Add another 40K and some of those 4 drop out giving a better than 10 to 1 ratio.

https://www.corvetteforum.com/forums...e-stats-7.html

Now you're going to say that it's not scientific evidence and I agree but there really hasn't been scientific evidence on this issue presented in this forum so why select me for ridicule?

davenp

31000 427s in C6s. Sample size of 51. Sample is small. Forum members are not wholly representative of C6 owners.

My response was intended to keep us objective, not call you out for lashing at the town square.

Mark2009

Lawrence, it's a terminology issue that had become so prevalent that I doubt most people, including yourself, are even aware of it (not intending to be critical here).

Clearly the LS7, and to an as yet mostly unknown extent the LS9, has valve guide problems. With the LS7 it appears from known samples that statistically probably over half have valve guide problems. Given what we've seen so far, over the course of 100K miles it is quite possible that 90% of them would have guides that are out of spec, but there is no data on how far out of spec a guide has to be before you start seriously risking valve problems. So, 10-30% out of spec may not cause a broken valve for the majority of engines, depending on how hard they are run, while 100-300% out of spec is surely going to be a serious problem for any engine in a relatively short number of miles.

So, 90% of the LS7's having guide problems by 100K miles is not an unreasonable claim.

But if someone reads your statement literally -- that 90% of the LS7's will have valve problems,which on this forum is pretty much taken to mean a dropped valve, then that would be an unlikely interpretation.

As always, get the guides checked on any LS7/LS9 ASAP and address as needed/desired... and this should be a normal inspection item, at every 20K miles or so depending on condition at time of last check.
.

LawrenceFromTorrance

There's objective and there's sticking your head in the sand and ignoring the obvious. I tend to agree with Mark on this issue. I think we're looking at the tip of an ice berg because most of the problem is hidden by the garage queens and the cruisers that hardly ever get over 4K RPM. Time will tell, I honestly hope I'm wrong because I've got two Z06s. One with a new set of heads and the other with two blown engines. I think that's 150% for me

propain

No you were successfully bashed and then back peddled after making a silly statement on how a SS valve will last "Longer" in the same environment where the OEM valve is breaking. When asked for any data to substantiate that claim you said "SS valves are stronger". Well duhhhh....

clogan

All I know for sure is that 100% of the Corvette Z06s I own have had bad guides. Of course, I only own one, but that's the one I had to pay to fix because GM wouldn't. Fortunately, it was fixed before any valve failures. (At least I hope it's fixed.)

propain

Exactly. In the same environment the SS and the OEM valve will break. Its certain as both valves are being subjected to stress far beyond their tolerances.

As we saw with Madsens car who was running SS valves with out of spec guides, the environment we see OEM valves failing in, his SS valves lasted a mere 10K miles before the head broke off and windowed the block. Then we have cars like Howie who got 86K hard track miles with out of spec guides running OEM valves. Its a crap shoot. You simply do not know when it will let go.

No valve will save you in that environment. Fix the guide issue and you fix the problem. Fix the guide issue and SS valves become useless in the stock or close to stock application.

ticat928

This is the kind of claim that would make a potential Z06 buyer look else where.
I for one (reading these forums) will only buy a low mileage Z06 if combined with a new crate engine (that has a 50,000 mile warranty) bottom lines at 2/3 the price of a base C7.

I would immediately pull the LS7 and spend the time come up with valve train components that keeps the roller tip centered on the valve stem tip (and lash cap) a maximum amount of time during the valve opening and closing events, it may take custom made rocker arms with a smaller ratio.

It is not going back in the car till I have the best of at every component level (titanium exhaust valves, beryllium valve seats, and forged pistons as well).

It is concerning that many head builders claim to have the best solution but none can explain why and/or back it up with solid data.

The LS7 valve train even challenged the the original design engineers in having a complete understanding.

Valve springs are critical, race car builder seem to able source higher quality, perhaps extra steps are required such as shot peening to close up micro surface cracks that can become stress risers after 10-thousands of cycles.

It may be worthwhile looking into some aerospace treatments for valve springs as well

http://www.summitracing.com/search/b...-crate-engines

above is the crate engine I would buy to hold station in the Z06 (2008+) till the LS7 is built proper

ticat928

Look Ma, over 7-min of hard running and no dropped valves:


It is the sound of the LS7 that makes it worthwhile to preserve it to eternity whatever it takes.

Mark2009

There is no history of issues with the stock LS7 valve springs, and in fact they seem to be a fairly advanced item (ovate beehive). I have read a few builders that think they are a little low on pressure for their tastes, but Spintron tests don't seem to bear that out (at least with stock valves).

ticat928

I am looking to raise the rev capability, but still observe the stock red line, I want to raise the fuel cut to 7400-rpm, since it is very harsh treatment of the engine when after 1/2-hr of road racing valves and cats are at their limits in temperature, not a good time to introduce a transient lean condition and loose the cooling fuel spray. Many clutches when hot hang slightly and allow revs to overshoot when clutch re-engagement lags slightly.

I am still on the fence in the solid vs hollow valve debate.

I may decide after trying my own blueprint method; I would buy 10-extra
OEM exhaust valves, then excite the valve like a tunning fork while holding near a mic and frequency analyzer; the 8-valves that exhibit the highest frequency and longest decay will most likely have the least metallurgical imperfections at the interior of the friction welded joint.

MyLastCorvette

How about reading the results prepared by experts like Katech, Lingenfelter, or the real life results of WCCH. If for some reason I couldn't trust the experts, had access to high tech radiology equipment. (and knew what I were looking at, like the proper forged gains/porsity of the test piece in question). In any case I wouldn't be listening to frequencies, hoping to ease my mind, regarding potential metal failures. PS Unless you had a perfect comparison, piece; How would you know what to listen/judge for. And just how would you know the comparison part was perfect, unless you X-ray?...

Dirty Howie

With all due respect I did not back peddle one inch and have no need to. My position is very clear and simple for anyone who looks at my statements. My position was not pulled out of my a$$ but rather gleamed from those in the know.

Why don't you address Ticat928 and those sources he mentioned.


DH

ticat928

"We only provide solid stem designs through Comp Cams, but the hollow stems certainly provide lower mass. Theoretically, these would be the best way to go, but there are very serious manufacturing and inspection hurdles to jump when producing a hollow valve. The question becomes, "Where is the safest and best way to invest my money when building this engine for this specific application and within this budget?" Sometimes your answer will be a hollow valve, but in most cases it would probably be a solid valve stem, unless we see a major technical jump on the manufacturing side. As the OEMs start pursuing that route on the mass-market side, we could find new technologies available to make these parts on the performance and racing side. We have certainly seen that effect with the availability of several new Beehive valve springs and now nitrided flat tappet cams that we offer. Just a few years ago, we could not provide either of those technologies dependably, at a high level and for a reasonable cost, but lower machine cost (although the cheapest machine was still on the order of a quarter-million dollars plus) for the tools to manufacture these parts became available in recent years. Per Griffin, solid stems are stronger, hollow stems are obviously lighter, but the quality control of an inside stem surface is very difficult to control. Because of the pounding of the valve upon closing, the sensitivity to failure is compounded if there are machining marks that can neither be controlled nor removed because they cannot be seen."

Quote above taken from this article published June2 2009:

http://performancebiz.com/features/v...designs-part-2

Have the OEM's such as Chevrolet found a major technical jump on the manufacturing side?

I do not know, have the 2-pc valve part #'s changed over the years?

GM has a record of hiding design changes to avoid class action suits on earlier inferior parts (ignition switch)

ticat928

"There is some debate about the efficiency
of this heat transfer, due to
concerns that the heat transfer to the
guides increases guide wear. Even
given these concerns, it’s interesting
to note that the Chevy LS7 engine
features sodium-filled exhaust valves
(along with titanium intake valves)."

"Hollow-stem
valves tend to work great on the intake
side, but are much more difficult
to manufacture and to inspect for defects
on the I.D. surface. Many upper-
echelon engine builders shy away
from hollow valves for that reason in
endurance (NASCAR or 24-hour
style) racing."

Above quotes taken from this article:

http://www.motor.com/magazine/pdfs/072011_07.pdf

ticat928

Fact: radiology equipment will not spot the minute internal defects that can result in failures below the MTBF calculated by the design engineers.

Fact:"The resonance frequencies of materials actually reflect on the strength and distance between atoms in the material."

Above quote taken from:

http://www.madsci.org/posts/archives...3670.Eg.r.html


It requires no knowledge other than the 8-valves with the highest resonance frequency are strongest you can put in the engine,

Mark2009

The hollow valve discussion should be moved -- by the participants -- to a different thread since, without fail, it derails into acrimony in whatever thread it appears in.