Cheesecake 07

I know its been debated...I've read plenty of threads but they seem to end in a stalemate. I like the idea of keeping the weight down of the valve train even at the extra expense as opposed to adding heavier material that might not only not solve any "problem" but might add new ones over time.

My car is an 07 Z with LT's, CAI and a tune. It's warranty is up. I use is it as a weekend, freeway on-ramp warrior with the occasional trip down the 1/4 for giggles. I don't believe that the LS7 is a turd and will, without a doubt dump an exhaust valve on me but there are enough threads on it that concern me due to the warranty being up and the extreme damage thats caused when it happens. That being said I don't plan on internal mods(cam, porting etc etc)...so

1. Would a set of Del-West Ti exhaust valves be reliable long term? Long term being over 60,70, 80k miles?

2. Assuming my exhaust guides fail and beat up the exhaust valves... would a Ti valve be less likely to snap in half and take out the long block? The thought of a thrashed head is easier to swallow then a trashed longblock.

My car has 17k miles on it so chances are the heads are fine. My thought was pulling the heads, sending them off for Ti exhaust valves, new stock beehive springs, rockers trunioned and guides(if needed). The $1500 or so would be cheap insurance for a guy like me that has no warranty left and isn't a track junkie.

Sorry if this has been a beat up topic but any opinions are appreciated..

Zo3o6

Im also looking at all the options... Im already modded (cam and springs), so i am leaning towards the SS exhaust valves.
Ron

jedblanks

going through the same thought process.

Seriously considering comp cams rocker trunion upgrades (both for LS7 and for my 97 cammed LS1 too). Have aftermarket warranty through 2/13, but I'm sure it would be a fight if the LS7 went boom. Thinking more stable rocker arms with less play are less likely to stress the guides by putting side loads on the valves. The posts about less noise are also appealing.

Apprehensive to tear heads off a 15,000 mile car and put SS valves in, but if it must be, then it must.

Car is strictly a weekend warrior with no track time at all, its an 07 Bone stock paper filter. IMO sitting in one spot is no better for the car than tracking them

Found this tool which seems like it would make the upgrade a DIY with a small vise.

Michael_D

I have researched this quite a bit. I am not in favor of adding valve train weight. At 7000 rpm, an additional 6 grams can lower peak rpm by as much as 500 rpms. Adding weight over OEM design also affects valve train stability modeling. Adding spring pressure to compensate increases friction. I had intended to run Ti exhaust, but after having numerous conversations with some of my contacts with more LS based race engine building experience than I, I have decided to stick with the OE exhaust valve, or go with a custom hollow stem valve. My heads are currently with my head porter and he is in the process of micro polishing the valves to determine if I can re-use them all or if I need to replace any. (Three exhaust and two intake are questionable).

In regards to the exhaust valve in particular, you can run Ti, but it is a costly retro-fit. For one, the valves range in price from roughly $70 - $110 each (jobber price). Del West will make them, but they are special order. Ferrea will also make them, but again, anther special order deal. Trick Ti will also make them, but yes once again, special order, as well as Manley and Xceldyne. Del West and Xceldyne are the premium pieces and the only valves I would consider using. In addition to the valve costs, you have to replace the seats with Mold Star 90 seat material or the valve head will get hammered into submission. The seats run about $30 each, plus machining. The upgrade, depending on who does the work, can run in excess of $1000. The Ti valves should also be coated, micro polished, and have hardened seats and tips (or you can use lash caps).

If you wish to keep the exh valve weight at or near OEM, the only other option is to run a hollow stem valve, or the OEM valve. So at this point, you need to rationalize why you want to replace the OE valve. If you are afraid of running a two piece valve, you need to come to the realization that the OE intake valve is a two piece valve. So ask yourself why you think two piece valves are inadequate. While you are contemplating the virtues of solid verses two piece, keep in mind that the higher end valves are all two piece, and in many cases, three piece valves. Also, if you had a picture of the grain structure of these high end two piece valves and compared it to solid valve that had been machined from a blank, your opinion may change.

There are no off the shelf, 8mm hollow steam valves available for these heads. Ferrea will make them, but only in batches. I believe the minimum order is 100. There are however 5/16” hollow stem valves available that will work with these heads, but they do require some extra machine work. There is one particular valve that I have been considering, and it’s made by Sinus, an Israeli company that I do not have personal experience with. It is a coated 5/16” hollow stem valve with hardened seat and tip. Quite expensive at about $60 each. My head porter uses them for extreme duty race applications where the engine sees extended periods of time at or above 8000 rpm. They are overkill, according to him.

So back to the OEM valve…… What’s wrong with it?? Well, opinions very. This may be hard to believe, but there are many, very reputable race engine builders who prefer to use the OEM valve, including off shore racing teams, and GM racing teams. LPE and Katech also use the OEM valves. My head porter uses them and he has worked hundreds of these heads, (mostly race orientated). I have spoken to a couple guys who work for GM’s race division, and they use the OEM valves. I have had a couple bad experiences with hollow stem sodium filled valves, but they were Ford FE engines and manufacturing and machining on these pieces was poor in comparison to today’s standards. This is something that I have had to come to grips with and let go...

I will know more in a few days after I have a chance to speak with my head porter (who is also working with my cam guy). I have asked him to give me options. After the port work is finished and we have flow / velocity numbers, my cam guy will know what cam I need to run, which will determine what spring to run (assuming valve weight remains the same). My primary goal is to have a very stable valve train up to 7500 rpm. I want to have a bit of head room above peak power.

AirBusPilot

IMO, the SS solid stem exh valves are just a band-aid, and do nothing to address the root problem, which is high valve guide wear (which occurs in random heads).

If you have high guide wear, the valve will move back and forth as it seats, creating a bending motion side to side. This will eventually cause the two piece valve to break at it's neck. A solid valve will resist this much longer.

It's also my understanding the solid SS valve won't transfer heat very well, unlike the oem sodium filled valve. I don't know how big an issue this could be.

Those of us that try to keep track of these kind of failures have yet to see a model year 09' engine have this problem. It might just be a matter of time, or GM may have finally fixed it. My theory is that the supplier made a few thousand bad guides and GM finally caught it, or they finally used them up by 09'.

Or, I'm just whistling past a graveyard.

MitchAlsup

I looked into Ti valves for a non LS motor a while back. I found the guys who built the Infinity INDY car motors (Tom Hooker). Their conclusion was if you are willing to pull the heads at 30K intervals and redo the seats and retension the springs, Ti valves are just fine.

But Ti especially in the exhaust area has a problem steel valves do not have. The spring tension (seat pressure) over time will cause the valve face to bow allowing the valve stem to retreat up the guide and relax the spring pressure. This is supposed to be a problem with white-metals (Ti) that grey-metals (steel) do not have.

The Infinity guys used a thick faced valve face to ameliorate the issues in that engine.

I do not understand how the motorcycle engine guys make the Ti valves last as long as they do.

jgaches

In many cases, they don't. Many CR450 owners swap out to SS for the very same reason. Valves pull up into the seat like an inside out umbrella on a windy day. In a pretty short period of time they can no longer get any valve lash.

jimman

Interesting article to keep you busy: Also there is an article by Katech showing by test that the stainless start to bounce just before redline.


Are stock valve materials good enough, or do you need to upgrade to valves that are made of a more durable alloy? If so, what kind of alloy? These are questions every engine builder must answer when selecting valves for performance engine applications.

To the naked eye, most valves look pretty much the same. Unless you're Superman and have spectral x-ray vision, one alloy looks pretty much the same as another - with the exception of coated titanium valves or steel valves that have a black nitride coating. But even with these valves, the visual difference is the coating material not the alloy.

To understand valve alloys, you need to know something about basic metallurgy. There are essentially two basic types of steel used to make valves. One is "martensitic" steel and the other is "austenitic" steel. The difference is in the microstructure of the steel and how the various ingredients in the alloy interact when the molten steel is cast and cooled. This affects not only the hardness and strength of the steel, but also its corrosion resistance and magnetic properties. As a rule, martensitic steels are magnetic while austenitic steels are non-magnetic.

In martensitic steel, the steel is "quenched" (cooled) very quickly from a molten state to freeze the grain structure in a particular configuration. Under a microscope, the grain structure has a needle-like (acicular) appearance. This makes the steel very hard but also brittle. Reheating and cooling the steel (a process called "tempering") allows some of the martensite crystals to rearrange themselves into other grain structures which are not as hard or brittle. By carefully controlling the heat treatment and quenching process, the hardness and tensile strength of the steel can be fine tuned to achieve the desired properties.

Steel alloys with a martensitic grain structure typically have a high hardness at room temperature (35 to 55 Rockwell C) after tempering, which improves strength and wear resistance. These characteristics make this type of steel a good choice for applications such as engine valves.

But as the temperature goes up, martensitic steel loses hardness and strength. Above 1000° F or so, low carbon alloy martensitic steel loses too much hardness and strength to hold up very well. For this reason, low carbon alloy martensitic steel is only used for intake valves, not exhaust valves. Intake valves are cooled by the incoming air/fuel mixture and typically run around 800° to 1000° F, while exhaust valves are constantly blasted by hot exhaust gases and usually operate at 1200 to 1450° F or higher.

To increase high temperature strength and corrosion resistance, various elements may be added to the steel. On some passenger car and light truck engines, the original equipment intake valves are 1541 carbon steel with manganese added to improve corrosion resistance. For higher heat applications, a 8440 alloy may be used that contains chromium to add high temperature strength. For many late model engines (and performance engines), the intake valves are made of an alloy called "Silchrome 1" (Sil 1) that contains 8.5 percent chromium.

Exhaust valves may be made from a martensitic steel with chrome and silicon alloys, or a two-piece valve with a stainless steel head and martensitic steel stem. On applications that have higher heat requirements, a stainless martensitic alloy may be used. Stainless steel alloys, as a rule, contain 10 percent or more chromium.

The most popular materials for exhaust valves, however, are austenitic stainless steel alloys such as 21-2N and 21-4N. Austenite forms when steel is heated above a certain temperature which varies depending on the alloy. For many steels, the austenitizing temperature ranges from 1600° to 1675° F, which is about the temperature where hot steel goes from red to nearly white). The carbon in the steel essentially dissolves and coexists with the iron in a special state where the crystals have a face-centered cubic structure. By adding other trace metals to the alloy such as nitrogen, nickel and manganese, the austenite can be maintained as the metal cools to create a steel that has high strength properties at elevated temperatures. Nitrogen also combines with carbon to form "carbonitrides" that add strength and hardness. Chromium is added to increase corrosion resistance. The end product is an alloy that may not be as hard at room temperature as a martensitic steel, but is much stronger at the high temperatures at which exhaust valves commonly operate.

Though austenitic stainless steel can handle high temperatures very well, the steel is softer than martensitic steel at lower temperatures and cannot be hardened by heat treating. To improve wear, a hardened wafer tip may be welded to the tip of the valve stem. Or, on some applications an austenitic stainless valve head may be welded to a martensitic stem to create a two-piece valve that has a long wearing stem and heat resistant head. The only disadvantage with a two-piece valve is that it doesn't cool as well as a one-piece valve. The junction where the two different steels are welded together forms a barrier that slows heat transfer up the stem.

21-2N alloy has been around since the 1950s and is an austenitic stainless steel with 21 percent chromium and 2 percent nickel. It holds up well in stock exhaust valve applications and costs less than 21-4N because it contains less nickel. 21-4N is also an austenitic stainless steel with the same chromium content but contains almost twice as much nickel (3.75 percent), making it a more expensive alloy. 21-4N is usually considered to be the premium material for performance exhaust valves. 21-4N steel also meets the "EV8" Society of Automotive Engineers (SAE) specification for exhaust valves.

SAE classifies valve alloys with a code system: "NV" is the prefix code for a low-alloy intake valve, "HNV" is a high alloy intake valve material, "EV" is an austenitic exhaust valve alloy, and "HEV" is a high-strength exhaust valve alloy.

Unfortunately, you can't always tell what kind of alloy a valve is made from because different valve suppliers use different alloys as well as their their own proprietary names for their valve materials. Thus one manufacturer may call their intake valve material a "422 stainless alloy" while another refers to it as an "NK-842 stainless intake material." Without a thorough metallurgical analysis, you can't really compare one manufacturer's valve material to another's. But do you really need such a comparison? As long as the alloy does what it is supposed to do, it doesn't matter what they call it.

The bottom line here is that intake valves and exhaust valves both require different types of alloys. The same alloy can be used for both intake and exhaust valves (say 21-2N or 21-4N, for example), but the best results are usually obtained when different alloys are selected for the intake and exhaust valves. Why? Because an exhaust alloy that has good high temperature strength and corrosion resistance really isn't needed on the intake side, and it may not have the hardness and wear resistance of an intake alloy at lower temperatures. Even so, some companies sell the same alloy for both intake and exhaust valves while others offer different alloys for intake and exhaust valves.

Intake valves run cooler and are washed with fuel vapors which tend to rinse away lubrication on the valve stem. So for intake valves, wear resistance may be more important than high temperature strength or corrosion resistance if the engine will be involved in any kind of endurance racing. Exhaust valves, on the other hand, run much hotter than intake valves and must withstand the corrosive effects of hot exhaust gases and the weakening effects of high temperatures. Consequently, a premium valve material is an absolute must on the exhaust side - especially in turbocharged and supercharged engines and those that inject nitrous oxide to boost power.

As combustion temperatures go up, valve alloys that work fine in a stock engine may not have the strength, wear or corrosion resistance to hold up in a performance application. If you want the valves to last, especially in a highly modified racing engine, upgrading to better valve alloys will be a must.

The best advice is to follow the valve alloy recommendations of your valve supplier, and to rely on their expertise when it comes to picking the best valve material for a performance application. If a stock valve alloy is holding up well enough in a performance application, there's no need to upgrade. But if an engine is experiencing valve burning or premature valve failure, then an upgrade to a better material may be needed to solve the problem.

Performance Valve Alloys
Materials that may be used for performance valve applications include carbon steel alloys, stainless steels, high-strength nickel-chromium-iron alloys and titanium. The alloys that are most commonly used for performance engines include various high chromium stainless alloys for intake valves, and 21-4N (EV8) for exhaust valves.

Inconel® refers to a family of trademarked high-strength austenitic nickel-chromium-iron alloys (a "superalloy" material) that is sometimes used for exhaust valves because of its superior high temperature strength. Inconel is a nickel base alloy that is sometimes thought of as a super-stainless steel, with 15 to 16 percent chromium and 2.4 to 3.0 percent titanium. Inconel 751 is classified as an HEV3 alloy by SAE. This alloy has been used for the exhaust valves in some late model GM medium duty truck engines (to prevent premature valve erosion), but is not commonly used in performance exhaust valves. For most performance applications, the exhaust valve material of choice is 21-4N - or titanium.

Titanium is often viewed as the ultimate valve alloy material because of its lightness. Titanium is about 40 percent lighter than steel, making it a good alternative for high revving engines. Lighter valves also allow more radical cam profiles that open and close the valves more quickly for better off the line performance and low end torque. The durability of titanium is similar to that of stainless steel. But from a cost standpoint, titanium is way beyond any steel alloy. A single titanium valve may cost $70 to $90 or more. Spending $1,200 or more for a set of valves may be peanuts to a professional racer with deep pockets, but for the average guy that's a lot of money. Yet titanium valves are being used in many street performance engines as well as everything else. Titanium valves are even being used in some production motorcycle engines these days.

One supplier of titanium valves said they use the same alloy for both intake and exhaust valves: a 6242 alloy that contains 6 percent aluminum, 2 percent moly, 4 percent zirconium and 2 percent tin. But a different heat treatments are used for the intake valves and exhaust valves. The heat treatment is very important because it determines the ultimate strength and hardness of the metal.

Titanium valves are often coated with moly or another friction-reducing surface treatment to reduce the risk of stem galling. Coated valves are recommended for street performance applications, but may not be necessary in drag racing or circle track applications where engines are torn down and inspected frequently.

Titanium valves will work with stock valve guides and seats, but for the best results they should be used with copper beryllium seats (to improve heat transfer and cooling) and manganese or silicone bronze valve guides.

Performance Coatings
Valves often have stem and/or head coatings to enhance performance. Stock valves as well as performance valves usually have chrome-plated stems to protect the stem from galling when the engine is first started. Chrome-plating also helps reduce valve seal wear on engines that use positive valve seals.

The thickness of the chrome plating can vary from a thin flash of .0002? to .0007? up to a hard plating of as much as .001?. It's interesting to note that chrome plating actually produces a rougher, not smoother, surface. But microscopic cracks in the surface of the chrome retain oil and improve lubrication to reduce wear.

Many Japanese OEMs use a black nitride coating on the valves instead of chrome plating. The nitride coating, which is applied in a salt bath treatment, protects the stems against scuffing and wear. Nitriding creates a thinner but harder surface layer that also does an excellent job of reducing wear.

Some performance valves may also have the stems treated with a special dry film lubricant to reduce friction and wear. With titanium valves, a dry film lubricant coating can also reduce the effects of valve erosion caused by the hot exhaust gases as they exit the combustion chamber. Dry film lubricants on the stem and inside of the valve head can also reduce the build up of carbon deposits that can create turbulence in the incoming air/fuel mixture and exiting exhaust gases.

As for the valve face, various coatings may be used to increase heat and wear resistance in valves made of steel or Inconel. Stellite is a hard facing material that's often required for heavy-duty diesel and gasoline exhaust valve applications, and may be used in some Top Fuel applications. Stellite is a cobalt base material with a high chromium content. It is applied to the valve face to protect against oxidation and corrosion. It may also be used on the stem tip for added wear resistance.

Ceramic thermal barrier coatings may also be applied to the combustion side of the valve head to reflect heat back into the combustion chamber. The theory here is that a heat reflective coating helps the valves run cooler. This helps the exhaust valves run cooler and last longer, and reduces heat transfer from the intake valves to the incoming air/fuel mixture for a denser, more powerful mixture. Heat reflected back into the combustion chamber also improves burning efficiency and power.

40YRW8

Jimman,
I don't know whether you wrote this or copied it but, either way, Thank You!
Gary

AirBusPilot

The stock LS7 intake valves are titanium.

hapnermw

'Also there is an article by Katech showing by test that the stainless start to bounce just before redline.'

Here's a link. It is worth reading ...

http://gmhightechperformance.automot...nce/index.html

This test used the PSI-LS1511 beehive valve spring that Katech recommends for the stock valves with their cams. As shown by this test, these springs won't properly control SS valves near redline. What spring will control a 100gm valve at 7100 rpm? There are many available that claim to have the nose pressure and high rpm stability required.

Do higher pressure springs require better lifters such as Morel High RPM lifters (Katech uses these in some of their engines)

'Morel proprietary steel alloy lifter bodies - micro polished for reduced friction
•Revolutionary internal design supports high RPM stability
•Large .750" diameter roller lifter wheel dispenses load over a wider range and takes full advantage of aftermarket camshaft profiles
•Able to withstand higher spring pressures than competitors' units
•Secured link bar system pairs lifters together - ideal for race applications'

These lifters aren't cheap and neither are the springs so the total with SS valves will be over $1000.

Many of those getting new valve guides have chosen to use SS values and springs with higher nose pressure. I've yet to hear of any one of these folks complaining of valve float at stock redline. I've also not heard of anyone testing the stability of this revised valve train on an Spintron, valve train simulator, etc. so this is the best data we have on whether this adhoc valve train engineering exercise works or not.

Sodium valve separation is one issue. Sodium valves are also associated with high valve guide wear due to a design that concentrates heat in the area of the stem in the guide.

Could sodium valves be a factor in causing excessive LS7 exhaust valve guide wear? Possibly.

Would racing engine builders be worried about this? Likely not, since this is more of a street longevity issue.

Until I hear about LS7 engines with SS exhaust valves/springs experiencing valve float; excessive valve guide wear; etc.; I can only assume that while SS exhaust valves are not optimum for a 7100 rpm valve train, with stronger springs and possibly Morel lifters, they work.

The stock valve train also works as does the one with PSI beehives Katech has Spintron'ed, until a valve separates ...

AirBusPilot

The LS6 uses sodium, two piece valves w/o issue.

Cheesecake 07

You guys are animals, I appreciate the insight...

For all the points you went over, I guess that's my problem is that I'm not real convinced theres anything wrong with the stock valve and going to SS valves doesn't seem like great solution either. However if the SS valve is stronger and will bend but not break and will trash a head as opposed to a longblock, that would be a win for me...assuming the worst anyways.

But again you guys make good arguments against the heavy valvetrain as well. Then I think well if Im gonna do SS valves, I might as well do a cam, if I do a cam I should port the heads...then the itch is a disease

Awesome info...even though you guys pee'd in my Ti valve cereal

Kinda back to square one... Kind of leaning towards pulling them and having them looked at and see where they are at. Just peace of mind.

Thanks again

jedblanks

Are there examples of exhaust valves/guides from LS7s with no unusual wear?

Michael_D

I try not to express my opinions too much on this sight. There's little use doing so when an audience already has their mind made up. So I will not do so now either....

Having said that, it would be wise to consider the conditions that would cause a hollow stem valve to separate, and keep in mind that these conditions can also cause a solid valve to separate as well....

Valve bounce, excessive seat to guide concentricity and PTV contact. If you eliminate the causes of these conditions, then they will not occur. You do this by concentrating on a stable valve train and good head work. When someone decides to 'engineer' a valve train, without the aid of extremely expensive equipment, then they very well could make things worse than they were before they started.

I have had numerous conversations with people who build crazy sick LS7 race engines (as an engine builder myself, it tends to open doors that are normally shut). They use the oem valves for most of these builds. They do not have exhaust valves dropping. You really need to take what your read on forums with a grain of salt. There are a lot of agendas and self serving opinions on forums.

And I am not suggesting that you NOT use Ti, only that it may be money better spent elsewhere. It can be done, and they will survive a long happy life, but only if it is done smartly. IE: micro polished, PVA coating, good geometry and proper seat angles, Mold Star 90 seats and EGT's under 1400F. You don't hear about it much because it is normally somthing only done for engines running in excess of 8000 rpm.

Michael_D

Yes. Mine, and many others. Remember where you are asking this question. There is an illusion around here that this is the only place on earth where LS7's are being used.

jedblanks

So which springs are you using if you go with a heavier stainless valve?

Are you using those same springs on the intake side when using stock Titanium Valve? Or staying with the stock spring?

'06 Quicksilver Z06

Variety of spring choices out there for various cam and valve setups.

There are at 180 people listed here who are running a heavier than stock exhaust valve in an LS7. Some, aside from the heads, otherwise stock, some cammed The names are hyperlinked. Click on a few of them, and check to see which springs they are running. Some will tell you.

Same spring for both intake and exhaust valves.

jedblanks

Clicked on 10 or 12 before posting the questions...didn't find too much. Clicked on 10 or so more after and found one person with this
-Patriot Performance Xtreme spring set
-Titanium intake valves, Rev SS exhaust valves

I was planning to run the same valves and I guess the I'll go with Brian Tooley .660" Lift Platinum Spring Kit with Tool Steel Retainers

I was looking for a Beehive kit that would work with aftermarket valve guides. Not smart enough to find it.


Any reason why you would put the extra pressure (over stock) on the stock intake valve if it's not required to control it?

'06 Quicksilver Z06

What you can do is select one of the names, read his post and either check his profile, or do a search using his name and the keyword "springs", and this might help.

Spring selection was based on not just valve weights but the cam profile.

There are a few good articles on that if you are interested.

Here are two:

http://classicinlines.com/springs.asp

http://www.enginebuildermag.com/Arti...e_springs.aspx

Also, notice how when an owner does a "cam only" setup, the camshaft "kit" will come with a set of different springs or spring recommendation than stock. Even though the valves have not been changed.
http://www.lgmotorsports.com/product...oducts_id=1399

Also, Michael_D put up a couple of informative posts on this a little while back, both of them in that same thread I referred you to earlier:

http://forums.corvetteforum.com/c6-z...post1582701116

http://forums.corvetteforum.com/c6-z...post1582690819