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I had the heads for my LS7 worked on by Advanced Induction in NC because they specialize in LS7 heads and reportedly, have very good results in preventing valve drop issues. I haven't had mine for very long so can't yet comment personally on durability.
I had the heads for my LS7 worked on by Advanced Induction in NC because they specialize in LS7 heads and reportedly, have very good results in preventing valve drop issues. I haven't had mine for very long so can't yet comment personally on durability. http://advancedinduction.com/index.php
While some shops go above and beyond with their porting and factory ls7 head services to be sure that there are no further issues, it can happen still... To be sure it won't ever happen, would be to buy an aftermarket casting. But the factory head, with work done can be a serious contender still and I have seen them make more power than even a brodix.
The whole issue is the LS7 ports are raised and have more unsupported valve between the valve guide and valve head. Combine that with RPM and maybe (definitely) some valve float and eventually the valve head breaks off. The "fix" is to install a longer valve guide.
The whole issue is the LS7 ports are raised and have more unsupported valve between the valve guide and valve head. Combine that with RPM and maybe (definitely) some valve float and eventually the valve head breaks off. The "fix" is to install a longer valve guide.
The whole issue is the LS7 ports are raised and have more unsupported valve between the valve guide and valve head. Combine that with RPM and maybe (definitely) some valve float and eventually the valve head breaks off. The "fix" is to install a longer valve guide.
Doesn't sound right, no offence. Because how and why do so many other raised port heads have the same unsupported valve, including aftermarket ls7 heads, and they're not breaking valve heads off. Are they all running much longer guides? They don't look it to me
I've seen 10 different "theories" as to why this happens to the factory ls7's. One guy was convinced the seats weren't machined parallel to the valve guides, in other words the valves were opening, and trying to close on a seat that's a few thousands skewed to the guide, so the valve heads are literally bending slightly every time they close.. which eventually leads to them breaking off
That does make sense to me. Imagine screwing a guide in just ever so slightly on an angle versus the valve seat, not enough the valve can't seal, but it's bending ever so slighty when it's forced shut by the valve spring .. would also explain the guides wearing out too fast .. which then just adds to the problem. You'd think the valve wouldn't seal properly if it was a few thousands off, but maybe it does
If what you said is true then every raised port head with long valves, even longer than the factory ls7, would be having issues .. my heads are ls7 from 24hr daytona nascars.. same basic port design as a factory ls7 head.. they use 2.10 / 1.55 titanium valves. The guides don't look extra long in them, they weren't sticking out like a tube. If the ls7 port design itself was the problem i doubt the engineers at ECR would have chosen it for 24hr daytona cars and stuck with getting the most out of a big CC cathedral head instead
These are the 24hr daytona nascar ls7 heads.. zoom in.. the guides don't look much longer than a factory ls7 head, but i never measured mine. If they are it doesn't seem like it would be by much at all . These heads also have both valves splayed 5 degrees, rather than parallel to the decks, so they are full custom, but the port height and cylinder head height is still basic LS7. The ports were slightly more raised at the bottom than a factory ls7 intake when i checked the fitment but it wasn't much, i forget now how much it was
If what you are saying is true then my valve heads will eventually fatigue and break off.. which would suck
You're right, I greatly abbreviated the explanation, but the "fix" for a factory LS7 head is still to replace the valve guides with new ones that are longer (including sticking out of the top as far as the spring and retainer will let you) and usually a thicker wall with as good of an alignment as you can get to prevent the valves from moving and shaking.
What I was trying to say is there is not something intrinsically wrong with the factory castings and the "fix" isn't brain surgery. All the rules for valvetrain geometry and stability still apply. I have a set of LS7 factory castings that have been "fixed" and the valve guide is clearly thicker around and sticking out further than the stock guide would have.
The whole issue is the LS7 ports are raised and have more unsupported valve between the valve guide and valve head. Combine that with RPM and maybe (definitely) some valve float and eventually the valve head breaks off. The "fix" is to install a longer valve guide.
There’s nothing at all wrong with the GM LS7 casting design….just ask GM.
In fact, the latest GM NASCAR head casting, the R07.2 uses LS7 port architecture and valve angle. I hear you guys screaming out there before you even begin to type in all caps, that it only has to last 500 miles! Your right. But…if there was an issue with geometry, or guide length, or the port height exposing a longer valve…GM wouldn’t even consider the design for their top tier racing program. Not a chance! Yes it’s only a 500 mile engine, but it’s an extremely harsh, constant high rpm environment with extreme temps. It’s an environment that finds the weak point of any internal engine design or part.
Now what the R07 head doesn’t have…and all other aftermarket LS7 heads don’t have…are the silly, weak, flexible rocker stands that the GM LS7 casting does have. They allow the rocker assembly to flex, which side loads the valve guides. The rocker stands are standalone and aren’t supported by anything. It’s a poor design in my opinion. I’ve seen the stands flex so much that they break right off the top of the port, when too much spring pressure is added. Aftermarket companies spotted the design flaw immediately and improved upon the design with their own reiteration of the rocker attachment area. This is my .02 of the issue anyway…
Scott, I think you're correct on the flexing rocker stands. Probably some heads are slightly more porous than others, making them even worse than the norm. What IS the norm?? A lot of this could've been helped/avoided by:
A: Going with a 356-T6 alloy, ala LS9,
B: Having the heads rotocast like the LS9,
C: Using 1.7 rockers instead of the less mechanical advantaged 1.8s. Make lift with the lobes, NOT a longer teeter-totter!
I'm also thinking GM inspects/blueprints the race shop heads, and may have them machined someplace besides Linimar.
There is a long list of reasons why many LS7s dropped valves. Valve seat concentricity was a big problem, as well as a poor manufacturing processes on the hollow stem exhaust valves causing them to break, also poor manufacturing processes on the intake valves, not having a thick enough CRN coating on the stem, as well as that coating being too rough and sawing away at the valve guides. There are also theories like Chevelle mentioned (which have a lot of merit) about rocker pedestals flexing, as well theories about the stock 1.8 ratio scrub type rocker causing too much side loading.
The bad news is, there is no fix that is fully proven out to be a set it and forget it solution, it would be very unwise not to check your valve guides on a fairly regular basis no matter who fixed them.
However, I have seen results from a couple of different solutions that have still had the valve guides well within spec at 20,000 and 30,000 miles. Both solutions used Ti/moly intake valves. But most people aren't willing to shell out the cash for that.
1) Katech ported stock heads with stock rockers, a 0.650" lift cam, Katech Ti/moly intake vavles, and CHE valve guides and they were within spec at 20,000 miles (If I remember correctly it was AZ Dave on CorvetteForum)
2) AHP Archangel heads. These are based on Brodix BR7 heads, they have AHP Ti/moly intake valves, and Moldstar 90 valve guides. A friend of mine who is a tuner up here in Michigan has a customer that put nearly 30,000 miles on a set of these and the guides were all still well within spec, unfortunately I don't know anything about the cam. However, he also had a set on his personal truck that had a 0.666" lift cam and revved to 8000 with stock rockers, and he said those are holding up great too.
My next set of LS7 heads are going to have Ti/moly intake valves, and probably CHE guides, maybe Moldstar 90 guides if my head porter is willing to install them, and hopefully be a head that uses very stout pedestals like a BR7 casting.
IMO, that is the BEST solution.
Side note: I know of a guy who had AI "fixed" heads and he recently dropped a valve destroying the entire engine. I doubt there is a single re-usable part in the longblock because it exploded so badly. My suspicion is that the failure is related to re-using the stock titanium valves (which 99% of fixed heads do) and having too rough of a finish causing the valve guide to wear, or the CRN coating on the valve stem failed.
Here is an example of what Scott - 70 Chevelle is talking about on the pedastal. Now there have been failures to completely stock engines but many of us put a bigger spring pressure. He is a set of OEM head and a set of Brodix heads done by AI. You will note the GM head is a pedestal while the Brodix head is a blob of aluminum with a notch cut out for the rocker arm. Note also the area where the valve cover bolts down (also a pedestal vs blob of aluminum) and how much aluminum is added there. BTW the Brodix heads weighs 5 pounds more than OEM 24 vs 29 pounds.
The Brodix are still pedestal mount. They are made of 356-T6, IIRC, so they are a better alloy than the 319 alloy OEM heads use. However, the factory heads also had a "blob of aluminum" cast in place. They are both cast pedestals. However, there's no doubt in my mind that the Brodix are superior.
12-29-2023, 08:39 AM
A lot of this could've been helped/avoided by:
