[Z06] WCCH bronze guides are shot
04-13-2018, 03:25 AM
#201
Team Owner
I don't remember the exact cost, I ballparked it, you're probably right that they cost more than $1200.
Like Nuke mentioned, tons of lift with stock rockers isn't ideal. I still think the stock Ti valve is the smoking gun in stock configuration. I'll be interested to see how my Mamo heads have worn with the PM guides and Ferrea Hollow Stem SS intakes/solid exhausts. In theory, with my YT roller rockers, guide wear shouldn't be bad. But this is the LS7 we are talking about....not a known giver of F's.
Like Nuke mentioned, tons of lift with stock rockers isn't ideal. I still think the stock Ti valve is the smoking gun in stock configuration. I'll be interested to see how my Mamo heads have worn with the PM guides and Ferrea Hollow Stem SS intakes/solid exhausts. In theory, with my YT roller rockers, guide wear shouldn't be bad. But this is the LS7 we are talking about....not a known giver of F's.
04-13-2018, 07:34 AM
#202
Team Owner
So the theory in intake valves being rough... is it that the dust/wear/etc then takes out the exhaust valves? How does the rough intake valve take out the exhaust guide, or are we talking that is only for the intake guides?
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
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Innovate (04-13-2018)
04-13-2018, 08:28 AM
#203
You have 2 things here....
stock heads failing from poor machining then fixed heads failing due to rough intake / soft guide.
Either go bronze + coated ti (or ss valve), or polished ti and harder (pm / ms) guides.
stock heads failing from poor machining then fixed heads failing due to rough intake / soft guide.
Either go bronze + coated ti (or ss valve), or polished ti and harder (pm / ms) guides.
04-13-2018, 08:48 AM
#204
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So the theory in intake valves being rough... is it that the dust/wear/etc then takes out the exhaust valves? How does the rough intake valve take out the exhaust guide, or are we talking that is only for the intake guides?
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
04-13-2018, 09:14 AM
#205
Drifting
So the theory in intake valves being rough... is it that the dust/wear/etc then takes out the exhaust valves? How does the rough intake valve take out the exhaust guide, or are we talking that is only for the intake guides?
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
. I will run them and check every 10-15k miles.
04-13-2018, 09:20 AM
#206
Team Owner
Which I'm about the only PRC aftermarket set I've seen tested. The others were stock casting/stock valves with just a CNC job, which if it is a finish issue contributing then makes sense.
Anyways, off to Costa Rica for a week to disconnect from reality. I wonder how many new valve threads in the week I'm gone.
Anyways, off to Costa Rica for a week to disconnect from reality. I wonder how many new valve threads in the week I'm gone.
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Innovate (04-13-2018)
04-13-2018, 11:00 AM
#208
Drifting
You guys are missing an important fact. The molybdenum coating is very expensive. Titanium valves with molybdenum coating would have priced Chevrolet out of market for use in a production engine. The LS7 would have been a very different engine with a 6500 rpm red line. Even with Del West perfecting the chrome-nitride coating and greatly improving their efficiency and cost reduction, the intake valves cost more than Chevrolet planned on spending. I believe this why the Chevrolet did NOT include this polishing process in the specification for the LS7 intake valves.
We are not seeing C7 Z06 with LT4 engines with worn out intake guides. Because Chevrolet did include this polishing process in the specification for the LT4 intake valves. So there is nothing wrong with Titanium valves with the chrome-nitride coating that has been polished and used with PM or MS90 guides.
As Katech has pointed out, their Titanium valves have "chrome nitride coated on the whole valve like the OEM one, but then the stem is coated with molybdenum" which works just fine with bronze guides.
We are not seeing C7 Z06 with LT4 engines with worn out intake guides. Because Chevrolet did include this polishing process in the specification for the LT4 intake valves. So there is nothing wrong with Titanium valves with the chrome-nitride coating that has been polished and used with PM or MS90 guides.
As Katech has pointed out, their Titanium valves have "chrome nitride coated on the whole valve like the OEM one, but then the stem is coated with molybdenum" which works just fine with bronze guides.
As I understand it, GM didn't approach Del West about the surface finish of the Ti intake valves until they were designing the LT4. (Very interested to see how these wear over time given that they are using PM valve guides on 1.8 rocker arm ratios, just like the LS7.)
Del West proposed tumble polishing the valves at the end of the manufacturing process and GM liked it so well, they started applying the same process to the existing LS7 intake valves. I believe the 2014 Z/28's with the LS7's have the tumble polished Ti intake valves from the onset.
The Mo coating on the back of the Ti valve stem is only necessary if you're running bronze guides, (Katech reiterates on their website that you only want to use these valves if you're running bronze guides.) Hibs article about the factory Del West Ti intake valves elaborates on the CrN process and reasons for it: essentially GM deemed bronze guides as "cost prohibitive" and moly-sprayed stems which would otherwise be typical an application using Ti valves is even more expensive than that.
https://www.corvetteactioncenter.com...-engine14.html
I had my stock heads done to Katech specifications. WCCH port, .030" mill, Ti/Mo intakes, new OEM exhausts, PSI springs, Ti retainers. They worked awesome for the <10k miles I used them before selling to a forum member. They showed zero wiggle upon removal. But the Intake valves alone were like $1200.
My .02..... the valve issue is mostly due to the use of the stock Ti valve. Putting new guides in with stock (or tumble polished stock) Ti valves just buys more time, but doesn't "fix" the issue.
My .02..... the valve issue is mostly due to the use of the stock Ti valve. Putting new guides in with stock (or tumble polished stock) Ti valves just buys more time, but doesn't "fix" the issue.
AHP measured the thermal conductivity of the GM PM guides used in the LS7 at 32 BTU's at 68°. Common bronze guides are slightly better at 48 BTU's but the more popular manganese bronze guides (greater hardness over common bronze guides,) are only 31 BTU's. The beauty is in the Moldstar 90 guides at 99 BTU's, along with their superior hardness qualities.
Point to consider is that the Moldstar 90 valve guides with CrN coated and tumble polished Ti intake valves is less expensive than moly-coated stemmed Ti valves and bronze valve guides. I believe either or when used with concentric valve guides will solve the issue, assuming of course, you run LS friendly cam lobes and reasonable amounts of lift. Even then, if you top off our valvetrain with the wrong or inferior springs, you could still have problems. It's a whole package solution, and each part of the package is important.
Last edited by BigVette427; 04-13-2018 at 11:02 AM.
04-13-2018, 01:13 PM
#209
Team Owner
04-13-2018, 01:50 PM
#210
I find it interesting that to GM, bronze valve guides are deemed cost-prohibitive even for the LS7 on a $70,000+ car in 2006.
Hibs article about the factory Del West Ti intake valves elaborates on the CrN process and reasons for it: essentially GM deemed bronze guides as "cost prohibitive" and moly-sprayed stems which would otherwise be typical an application using Ti valves is even more expensive than that.
https://www.corvetteactioncenter.com...-engine14.html
Hibs article about the factory Del West Ti intake valves elaborates on the CrN process and reasons for it: essentially GM deemed bronze guides as "cost prohibitive" and moly-sprayed stems which would otherwise be typical an application using Ti valves is even more expensive than that.
https://www.corvetteactioncenter.com...-engine14.html
04-13-2018, 01:59 PM
#211
Drifting
I believe you have misread Hib's article about the cost of bronze guides. Here is the direct quote "Most racers use bronze guides or some other type of aftermarket guide which is cost-prohibitive". Cost-prohibitive is NOT referring to bronze guides but to "some other type of aftermarket guide". I think he is talking Moldstar 90 for aftermarket guide.
04-13-2018, 01:59 PM
#212
Team Owner
Lol at $500 for anything on this car being "cost prohibitive".
04-13-2018, 02:10 PM
#213
Team Owner
For an OEM it is. They measure stuff down to a penny. I once read that the difference between a c5 interior and a 911 interior was something like $27.
04-13-2018, 02:43 PM
#214
Team Owner
True, and I get that...but I would tend to think that GM's economies of scale could source and employ MS90 for far less than than say AHP for example. I'm sure the bean-counters get to overrule the engineering dept all the time though.
04-14-2018, 12:50 AM
#215
Melting Slicks
So the theory in intake valves being rough... is it that the dust/wear/etc then takes out the exhaust valves? How does the rough intake valve take out the exhaust guide, or are we talking that is only for the intake guides?
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
Maybe that is why my PRC heads were great at 30k+ miles, because they had aftermarket valves that were not rough. Even with the .652 lift cam, and stock rockers, zero issues, and no wiggle at all.
It's hard to compare the behavior of your PRC heads with stock heads.
04-14-2018, 12:57 AM
#216
Melting Slicks
Seems like most of GMs focus has been reactionary, and it was a business decision to deny the existence of the issue and ride out the warranty claims versus doing a massive recall that would have cost more money. My opinion.
04-14-2018, 03:30 PM
#217
Instructor
Rough intake stems don't wear out exhaust guides. My WCCH heads with 31,500 miles on them and solid ss exhaust valves were just has worn or more than the intake side (I did not use a dial indicator) on the one cyl head I disassembled (Lt one) before sending them to AHP for moldstar 90 guides. And all valve stems were in spec.(I mic them) and all the valves were reused.
04-14-2018, 03:43 PM
#219
Melting Slicks
There isn’t one smoking gun to the issue. There are like 5. In scientific testing, in order to quantify causality, researchers seek variance. The closer to 1.00 of variance you get, the more likely it is that a certain phenomena caused another phenomena.
In the case of the LS7 valve guides, I’d wager that the use of Ti valves would result in greater variance than other influences (guide material, concentricity, rocker scrub, etc).
People can always poke holes in a multivariate theory, “well my exhaust was shot too” but this is to be expected with a multivariate problem. None of the theories are at 1.00 variance. All of them contribute. My opinion is that Ti valve in this production application results in more variance than the other factors.
In the case of the LS7 valve guides, I’d wager that the use of Ti valves would result in greater variance than other influences (guide material, concentricity, rocker scrub, etc).
People can always poke holes in a multivariate theory, “well my exhaust was shot too” but this is to be expected with a multivariate problem. None of the theories are at 1.00 variance. All of them contribute. My opinion is that Ti valve in this production application results in more variance than the other factors.
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Hirohawa (04-15-2018)
04-14-2018, 03:48 PM
#220
Instructor