Ls7 heads dropping valves
Teching In
Joined: Apr 2009
Posts: 27
Likes: 0
From: VA Beach
I'm thinking a set of Mast heads or TF's might just be in order with a cheater cam.
What are your thoughts?
Mario
Banned
Joined: Mar 2013
Posts: 1,137
Likes: 2
From: Studewood/Acres-Homes TX.
z0sicktanner I would like to give U a # for one of the head guy's at GM I would like to see what he would say when posed with this ? I would call and ask but U have more details,info than me...Would you like the #...
He is the head of the LSX cylinder head Division
He is the head of the LSX cylinder head Division
Banned
Joined: Mar 2013
Posts: 1,137
Likes: 2
From: Studewood/Acres-Homes TX.
Yeah......It's sad all they have to do is talk to a aftermarket head team and problem solved. Or buy a set of aftermarket heads and Do Research and development and presto....I wish they could pay me to work there I'd incorporate a lot more Nascar things into the production models.
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to be honest, I'm not surprised he hasn't heard of this. Why would he? He works in a big corporation, lot's of projects, R&D, future stuff, new bosses, budget planning, team hiring, planning, etc. I would expect it is not his job to scour forums to see if there are any issues with GM products. All these big companies work off of metrics/data that is collected and regardless of how big a deal we all think this is, this is probably not on anyone's radar as it is a small run of engines, small # of issues reported, small # of warranty claims paid (all my assumptions) such that you could see that they in fact would be completely clueless about this particular issue. In big companies there are just too many priorities and things going on to catch an anomaly like this.
Not defending them in any way, they should have a quality product to begin with, but I could see how this can get lost in the big corporate engine, it doesn't shock me at all.
Not defending them in any way, they should have a quality product to begin with, but I could see how this can get lost in the big corporate engine, it doesn't shock me at all.
Teching In
Joined: May 2010
Posts: 34
Likes: 0
From: Central Indiana
I am convinced that it is heat, and the fact that the valve absorbs more of it than in any other setup (being as the valve head is a larger percentage of the combustion chamber surface). It's simply too much heat for a single valve to dissipate reliably.
When my warranty is up, assuming I still want the car, I'll have the heads redone and the exhaust valves coated with a thermal barrier. Might also have oil squirters installed.
When my warranty is up, assuming I still want the car, I'll have the heads redone and the exhaust valves coated with a thermal barrier. Might also have oil squirters installed.
Teching In
Joined: May 2010
Posts: 34
Likes: 0
From: Central Indiana
AFAICT the only 'fix' would be to keep the valve from getting too hot - which means lower average combustion chamber temp, and/or rejecting the heat to something else. Hence my thoughts of barrier coatings and squirters. SS/solid-stem valves will slow the heating process down, but it'll still happen eventually.
I'd really be interested to know if anyone running straight E85 from the get-go has had valve issues, but then I suspect there just aren't many people doing that.
Im curious as to how you came up with this heat theory? Ive seen many a turbo charged set up get the pipes glowing red hot making huge amounts of power without this guide/valve issue.
Teching In
Joined: May 2010
Posts: 34
Likes: 0
From: Central Indiana
How many of those were two-valve heads? With LS7-sized valves?
I didn't invent this theory; a CF poster - and IIRC the first guy to do any kind of objective engineering-based analysis - who goes by 'hoefi' suggested it.
He's an engineer; I'm an engineer (well, in a past life anyway). It made sense. It's the only explanation that does make sense to me. I don't think it's the only problem - I believe there have been some machining issues, for example - but I think it's a fundamental design flaw that's the underlying root cause. The exhaust valve absorbs too much heat for the stem to dissipate; we don't see this in other LS engines because they have smaller valves - less surface area being heated - and they don't rev to 7000RPM, so the average heat load is lower.
With multivalve heads, you've got two stems dissipating the heat, and each valve has a much smaller heated surface area.
I didn't invent this theory; a CF poster - and IIRC the first guy to do any kind of objective engineering-based analysis - who goes by 'hoefi' suggested it.
He's an engineer; I'm an engineer (well, in a past life anyway). It made sense. It's the only explanation that does make sense to me. I don't think it's the only problem - I believe there have been some machining issues, for example - but I think it's a fundamental design flaw that's the underlying root cause. The exhaust valve absorbs too much heat for the stem to dissipate; we don't see this in other LS engines because they have smaller valves - less surface area being heated - and they don't rev to 7000RPM, so the average heat load is lower.
With multivalve heads, you've got two stems dissipating the heat, and each valve has a much smaller heated surface area.
