[Z06] What would YOU do to make your LS7 heads bulletproof?
08-31-2011, 01:15 PM
#21
Burning Brakes
Thread Starter
SS has 40% more weight and 40% less strength and thermal characteristics of a Cement Block. You want the heat transfer where do you expect it to go? Also I understand we have a lot of vendors that may use SS and appear to have no problems but they do not have the resources to properly vet this approach. Do you think that GM even with the bad press is going to go with a large displacement motor that can spin to 7K and guarantee it for 100K miles and then do it over 30,000 times? Ask your next builder if he can do that, food for thought. Please don’t kill the messenger just presenting published facts. The balance issue was explained in a later post on this thread, I still don't aggree with mixing the two with the weight differences. Also, no one has actually determined why there is a problem, if there is one. I have 143,000 miles on mine and I frankly have now concidered taking off heads to see how they look after all this talk.
Here's a couple of good quotes directly from Richard at WCCH himself. I've also posted this in the "Sky is NOT falling" thread because I think it's applicable to both.
Originally Posted by Richard@WCCH
We have definitely seen excessive wear in some LS7 exhaust guides. Mostly coming from engines with over 30k on the clock. We have seen some heads show inconsistent wear requiring only one or two guides needing replacement. It appears that the sodium exhaut valves are transmitting an excessive amount of heat from the stem to the guide. In some cases the oil is BBQ'd in the guide and the lack of lubrication and cooling from the oil causes the excessive wear (mostly in the lower half of the exhaut guide). We've measured some guides as having over .004" of wear in the lower 1" of exhaust guide length. Porsche 911's suffer the same type of related guide wear on the exhaust side.
The next item to note regarding the sodium exhaust valves relates to the wall thickness of the sodium exhaust valve stem. It's only .040" thick and makes for a fragile exhaust valve. GM uses a good quality steel material but the design spec. renders the valves brittle at the neck. Hence the reason we choose the replace the factory units with stainless or inconel. The exhaust valves we use are manufactured with a .001" oversized stem size which allows us to hone the exhaust guides and remove most or all of the taper in the bore. In cases with excessive wear we replace the guides with bronze.
I can't comment on weather the excessive guide wear is causing the valves to rattle around in the guide on on the seat causing the head failures. It may be due to excessive heat buildup from the restricted heat flow path to the guide. As I mentioned before, there's only 1mm of wall thickness at the valve neck. Not a good situation in engines producing high specific horespower. The stainless exhaust valves don't show the rapid wear that the sodium valves have.
We have definitely seen excessive wear in some LS7 exhaust guides. Mostly coming from engines with over 30k on the clock. We have seen some heads show inconsistent wear requiring only one or two guides needing replacement. It appears that the sodium exhaut valves are transmitting an excessive amount of heat from the stem to the guide. In some cases the oil is BBQ'd in the guide and the lack of lubrication and cooling from the oil causes the excessive wear (mostly in the lower half of the exhaut guide). We've measured some guides as having over .004" of wear in the lower 1" of exhaust guide length. Porsche 911's suffer the same type of related guide wear on the exhaust side.
The next item to note regarding the sodium exhaust valves relates to the wall thickness of the sodium exhaust valve stem. It's only .040" thick and makes for a fragile exhaust valve. GM uses a good quality steel material but the design spec. renders the valves brittle at the neck. Hence the reason we choose the replace the factory units with stainless or inconel. The exhaust valves we use are manufactured with a .001" oversized stem size which allows us to hone the exhaust guides and remove most or all of the taper in the bore. In cases with excessive wear we replace the guides with bronze.
I can't comment on weather the excessive guide wear is causing the valves to rattle around in the guide on on the seat causing the head failures. It may be due to excessive heat buildup from the restricted heat flow path to the guide. As I mentioned before, there's only 1mm of wall thickness at the valve neck. Not a good situation in engines producing high specific horespower. The stainless exhaust valves don't show the rapid wear that the sodium valves have.
Originally Posted by Richard@WCCH
Given the same conditions, the bronze guides will wear as well. The size of the small heat path must be increased. With a solid stem valve heat is allowed to travel further up the length of the stem. It provides a larger flow path for heat dissipation.
The primary heat path is through the valve seat. The secondary heat path is through the valve guide. Lean stoic. conditions at cruising speeds generate lots of heat on the exhaust valves with unleaded fuels. The heat bakes the small amounts of oil that makes it to the lower portion of the exhaust guide. Once the lubrication is gone there is metal to metal contact and on a molecular level electron sharing occurs. The steel molecues of the exhaust valve stem have a greater resistance to wear. The powdered metal guides have mixture of wear resisting alloys along with lubritious properties pressed into the matrix. You don't have to beat on the engine to experience valve guide wear.
The primarly reason we use bronze valve guides is because GM will not sell the guides separately. Rather they will sell you an entire replacement head. The aftermarket parts supply only furnishes bronze alloy valve guides. I personally like the powdered metal valve guides the factory uses but the supplier does not sell piece meal to the public. Additionally we have no long term wear issues with the bronze guides and solid stem stainless steel valves.
In the last decade GM has done a masterful job improving both metalurgy and rocker arm geometry to reduce overall valve guide wear. Rocker arm desings are also superbly executed. The issues seem to only be related to the sodium valves.
Given the same conditions, the bronze guides will wear as well. The size of the small heat path must be increased. With a solid stem valve heat is allowed to travel further up the length of the stem. It provides a larger flow path for heat dissipation.
The primary heat path is through the valve seat. The secondary heat path is through the valve guide. Lean stoic. conditions at cruising speeds generate lots of heat on the exhaust valves with unleaded fuels. The heat bakes the small amounts of oil that makes it to the lower portion of the exhaust guide. Once the lubrication is gone there is metal to metal contact and on a molecular level electron sharing occurs. The steel molecues of the exhaust valve stem have a greater resistance to wear. The powdered metal guides have mixture of wear resisting alloys along with lubritious properties pressed into the matrix. You don't have to beat on the engine to experience valve guide wear.
The primarly reason we use bronze valve guides is because GM will not sell the guides separately. Rather they will sell you an entire replacement head. The aftermarket parts supply only furnishes bronze alloy valve guides. I personally like the powdered metal valve guides the factory uses but the supplier does not sell piece meal to the public. Additionally we have no long term wear issues with the bronze guides and solid stem stainless steel valves.
In the last decade GM has done a masterful job improving both metalurgy and rocker arm geometry to reduce overall valve guide wear. Rocker arm desings are also superbly executed. The issues seem to only be related to the sodium valves.
Last edited by TORQJNKY; 08-31-2011 at 01:22 PM.
08-31-2011, 01:45 PM
#22
Le Mans Master
jimman, you still didn't give me your metalurgy explaination of SS compared to a cement block. SS doesn't transfer heat like the Sodium valves do through the stem, but they do resist heat better than the sodium valves do which promotes operational longevity.
Here's a couple of good quotes directly from Richard at WCCH himself. I've also posted this in the "Sky is NOT falling" thread because I think it's applicable to both.
Here's a couple of good quotes directly from Richard at WCCH himself. I've also posted this in the "Sky is NOT falling" thread because I think it's applicable to both.
Last edited by jimman; 08-31-2011 at 02:05 PM.
08-31-2011, 02:00 PM
#23
The Consigliere
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SS thermal conductivity is poor and one could say slow as compared to titanium. To further enhance the faster thermal conductivity sodium is used which is used in high temp environments. This was first used in the railroad industry and adopted by the Nuclear energy industry for high temp use. Now the purpose is to get an even heating profile over the entire stem which reduces the thermal impendence to allow better dissipation to the head. I would expect the valve head temp using SS to be extremely high and I would not think that is a good thing. Now if you’re having baked oil at the head of the valve with Titanium you certainly will have that with SS. Now he mentioned using SS for less wear characteristics, but I was lead to believe that the valve itself is not the wear issue but the guild.
So, if SS valves would concentrate more heat at the seat, and less to the guide, would one simply be transferring guide wear (from stock set-up) in exchange for premature valve seat wear/failure?
I'm not an engineer; just trying to follow along and learn. But that's what this farm boy would take from your comments.
Thoughts?
08-31-2011, 02:03 PM
#24
Le Mans Master
This is not uncommon at all.....I've built hundreds of race engines with titanium intake valves and inconel exhaust valves with no issue. As opposed to looking at the valve train as individual components it's important to think of it as a balanced system. As long as you have eight valves of one weight and eight valves of another weight the system will work just fine. (keep in mind spring pressure needs to differ for the intake verse exhaust valve)
If you want to take it a step farther.....under boost the intake valve needs to actually have more spring pressure to compensate for the increased load on the valve. (valve area x psi boost pressure). For example....my diesel truck runs roughly 80 psi boost pressure and the intake valves (two per cylinder) have 1.72 in surface area. So if 250 lb seat pressure is adequate for 30 psi boost I need significantly more to compensate for the added boost.
If you want to take it a step farther.....under boost the intake valve needs to actually have more spring pressure to compensate for the increased load on the valve. (valve area x psi boost pressure). For example....my diesel truck runs roughly 80 psi boost pressure and the intake valves (two per cylinder) have 1.72 in surface area. So if 250 lb seat pressure is adequate for 30 psi boost I need significantly more to compensate for the added boost.
08-31-2011, 02:04 PM
#25
Le Mans Master
So, if SS valves would concentrate more heat at the seat, and less to the guide, would one simply be transferring guide wear (from stock set-up) in exchange for premature valve seat wear/failure?
I'm not an engineer; just trying to follow along and learn. But that's what this farm boy would take from your comments.
Thoughts?
I'm not an engineer; just trying to follow along and learn. But that's what this farm boy would take from your comments.
Thoughts?
08-31-2011, 02:30 PM
#26
Melting Slicks
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St. Jude Donor '12
I am surprised that powdered metal guides have not been mentioned. They are impregnated with lubricant. I have been researching this and in a very good article I recently read, it stated that powdered metal guides should be used in place of bronze on high lift ls engines. Just food for thought and something to research.
08-31-2011, 02:42 PM
#27
Race Director
I am surprised that powdered metal guides have not been mentioned. They are impregnated with lubricant. I have been researching this and in a very good article I recently read, it stated that powdered metal guides should be used in place of bronze on high lift ls engines. Just food for thought and something to research.
.....
The primarly reason we use bronze valve guides is because GM will not sell the guides separately. Rather they will sell you an entire replacement head. The aftermarket parts supply only furnishes bronze alloy valve guides. I personally like the powdered metal valve guides the factory uses but the supplier does not sell piece meal to the public. Additionally we have no long term wear issues with the bronze guides and solid stem stainless steel valves.
....
The above was cut from a prior post on this thread and answered your question before you asked it.
Last edited by AzDave47; 08-31-2011 at 02:46 PM.
08-31-2011, 02:45 PM
#28
So now the debate is: to stay OEM sodium exhaust valves or to go stainless steel? Man there are good arguments on both ends here....I would think if the valves are in good shape and are not wearing, I would just keep them and use a better wear resistant oil and redo the guides to bronze with some yells terra roller rockers to help improve the side load. If Katech uses the oem valves, I'd say that is evidence enough to stay with them. But, I'm all ears in this thread because there are good arguments on both ends.
08-31-2011, 03:18 PM
#29
Burning Brakes
Thread Starter
SS thermal conductivity is poor and one could say slow as compared to titanium. To further enhance the faster thermal conductivity sodium is used which is used in high temp environments. This was first used in the railroad industry and adopted by the Nuclear energy industry for high temp use. Now the purpose is to get an even heating profile over the entire stem which reduces the thermal impendence to allow better dissipation to the head. I would expect the valve head temp using SS to be extremely high and I would not think that is a good thing. Now if you’re having baked oil at the head of the valve with Titanium you certainly will have that with SS. Now he mentioned using SS for less wear characteristics, but I was lead to believe that the valve itself is not the wear issue but the guide.
I think the reason Richard points to the sodium filled valve as the problem is because they promote premature guide wear due to valves inherent heat dissipation design. Richard even says in his quotes that he would use the OEM valve guides with a SS or Inconel valve if he could get the OEM guides. So the OEM guide is not the problem.
I think the cooling and light weight concept behind a hollow sodium filled valve has a lot of merit, but I think the design falls on it's own sword by being thin walled, brittle necked, and having a heat dissipation charateristic that causes premature valve guide wear.
08-31-2011, 03:33 PM
#30
Le Mans Master
I concur that a SS valve won't conduct heat through the stem as well as the sodium filled valve, so you may loose some overall heat dissipation qualities using a SS valve. Is it enough to cause problems, probably not because, it seems WCCH thinks it's the answer.
I think the reason Richard points to the sodium filled valve as the problem is because they promote premature guide wear due to valves inherent heat dissipation design. Richard even says in his quotes that he would use the OEM valve guides with a SS or Inconel valve if he could get the OEM guides. So the OEM guide is not the problem.
I think the cooling and light weight concept behind a hollow sodium filled valve has a lot of merit, but I think the design falls on it's own sword by being thin walled, brittle necked, and having a heat dissipation charateristic that causes premature valve guide wear.
I think the reason Richard points to the sodium filled valve as the problem is because they promote premature guide wear due to valves inherent heat dissipation design. Richard even says in his quotes that he would use the OEM valve guides with a SS or Inconel valve if he could get the OEM guides. So the OEM guide is not the problem.
I think the cooling and light weight concept behind a hollow sodium filled valve has a lot of merit, but I think the design falls on it's own sword by being thin walled, brittle necked, and having a heat dissipation charateristic that causes premature valve guide wear.
08-31-2011, 04:42 PM
#31
Team Owner
SS has 40% more weight and 40% less strength and thermal characteristics of a Cement Block. You want the heat transfer where do you expect it to go? Also I understand we have a lot of vendors that may use SS and appear to have no problems but they do not have the resources to properly vet this approach. Do you think that GM even with the bad press is going to go with a large displacement motor that can spin to 7K and guarantee it for 100K miles and then do it over 30,000 times? Ask your next builder if he can do that, food for thought. Please don’t kill the messenger just presenting published facts. The balance issue was explained in a later post on this thread, I still don't aggree with mixing the two with the weight differences. Also, no one has actually determined why there is a problem, if there is one. I have 143,000 miles on mine and I frankly have now concidered taking off heads to see how they look after all this talk.
DH
08-31-2011, 05:04 PM
#32
Burning Brakes
Thread Starter
I think it would be very interesting to know what jimman's valve train looks like also. But even if jimman's exhaust valve failed an hour from now, with 143,000 miles on the clock, it's a win for his car already.jimman, how is your car driven? Any track days, mods, daily driven, type of oil used etc...?
08-31-2011, 05:14 PM
#34
Burning Brakes
Thread Starter
08-31-2011, 05:34 PM
#35
Melting Slicks
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St. Jude Donor '12
Originally Posted by Richard@WCCH
.....
The primarly reason we use bronze valve guides is because GM will not sell the guides separately. Rather they will sell you an entire replacement head. The aftermarket parts supply only furnishes bronze alloy valve guides. I personally like the powdered metal valve guides the factory uses but the supplier does not sell piece meal to the public. Additionally we have no long term wear issues with the bronze guides and solid stem stainless steel valves.
....
The above was cut from a prior post on this thread and answered your question before you asked it.
.....
The primarly reason we use bronze valve guides is because GM will not sell the guides separately. Rather they will sell you an entire replacement head. The aftermarket parts supply only furnishes bronze alloy valve guides. I personally like the powdered metal valve guides the factory uses but the supplier does not sell piece meal to the public. Additionally we have no long term wear issues with the bronze guides and solid stem stainless steel valves.
....
The above was cut from a prior post on this thread and answered your question before you asked it.
08-31-2011, 06:01 PM
#36
Burning Brakes
Thread Starter
http://www.trickflow.com/partdetail....t=TFS-30600252
08-31-2011, 07:16 PM
#37
Burning Brakes
Okay, I get that. Let me re-phrase: is there a documented design flaw in the cylinder head that makes it prone to failure? Valve guides wear, regardless of material - the heat goes somewhere. Is it truly a design flaw, or is it the application of aftermarket parts? Is there enough evidence to suggest that everyone who has added a camshaft to their LS7 has catastrophic valvetrain failure pending, beyond normal wear characteristics?
08-31-2011, 07:38 PM
#38
Le Mans Master
Okay, I get that. Let me re-phrase: is there a documented design flaw in the cylinder head that makes it prone to failure? Valve guides wear, regardless of material - the heat goes somewhere. Is it truly a design flaw, or is it the application of aftermarket parts? Is there enough evidence to suggest that everyone who has added a camshaft to their LS7 has catastrophic valvetrain failure pending, beyond normal wear characteristics?
Last edited by jimman; 08-31-2011 at 07:47 PM.
08-31-2011, 10:03 PM
#39
Team Owner
There is more than a fair share of documented failures. What scares me more is besides the failures the number of heads with worn guides is very high from what I've seen. They aren't failing yet but the guides are wearing. I'm replacing mine because my friends guides were completely shot with 10k miles on the car. I bought brand new heads because I didn't want to wait to send them off, get them replaced and get them back. I'm selling my stock heads to recoup the cost of the new ones. I'll pay more but have very little downtime. Not a bad way to go if you only want your car down for a day or two. Get some heads ready to go then swap them.
08-31-2011, 10:05 PM
#40
Melting Slicks
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St. Jude Donor '12
The valve guide shown on the website says "powdered metal" but shows a bronze looking guide as an example. Doesn't look like it will work with the LS7 though.
http://www.trickflow.com/partdetail....t=TFS-30600252
http://www.trickflow.com/partdetail....t=TFS-30600252