Originally Posted by chadyellowz06

I've been porting cylinder heads for 26 years and I've never seen anything like this. The only LS heads that are wearing guides are the LS7 and LS9. the LS9 is wearing the intake guides because the Ti intake valve has a crap CrN coatings on these valves which varies from valve to valve even brand new ones right out of the box. Tumble polishing at Del-West helps but is far from a fix.

Now, for guides wearing from driving around town... every case I have seen of guides in spec have been from a 100% track car, stock or modded. To date I have seen 2 stock heads in spec, both 100% track cars only, one had 24k track miles but a ring land took out the intake valve when it broke. I have yet to see one LS7 head reworked that has been in spec and I've worked on most all of them. AHP are the only ones I have not seen yet, and I plan on trying those guides myself (I have to call them tomorrow at 11:30am to discuss).

The LS7 is a high compression ratio engine and most people mill heads for more for power. The more you mill the less timing can be run. And at low speeds to the store or a weekend drive, those EGT are hot. The retarded ignition timing will drive up the EGTs which in turn will increase the likeliness of knock occurring. The knock is then detected by the sensors and more timing is pulled again driving up the EGTs. It becomes a vicious cycle. Flat milling .045”-.050” will get the chamber volumes down to 62-63cc which will put the CR at approx. 12:1. Now this isn't the 100% cause because if it was we would be seeing worn guides in every engine with that CR weather it's an LS7, LS3, LS2, LS1, etc., and we don't, but it's not helping the issue.

People worry about valve bounce, but the ZL1 and CTS-V get modded a lot and those cars come with solid stem exhaust valves from the factory. Of course lighter is better, but 100g exhaust valves have been way past 7000rpm for over 50 years without wearing guides. I myself have worn out 3 sets of guides and will be pulling heads again this summer for the Moldstar-90 guide.

I can tell you this every valve job i've ever done never leaves until I get .001 run out. I've ported many heads for the LS7 and my work speaks for itself. In the reworked heads I've gotten, the guides have been bad every time. A guy I did a set of heads for last year had IPS Motorsports work the heads to be out of spec in 7k miles. In his heads it was not a valve seat concentricity issue as Ian's heads had a .002 run out with guides at at the .0050 mark on all 16 valve guides.

I have yet to see a LS9 head with worn exhaust guides, but I've seen worn intakes. Why? because I don't think Ti is a good valve to run in any street driven car. It eats guides and the coatings are pure ****. I'd run the Ti moly coated ones or run a 100g stainless intake valve and get the Ti valve out. Now this is just my opinion, and many may disagree, but I was posting about these heads wearing long before anyone thought there was an issue. Then, back in 2013, the bronze valve guides and solid stems starting showing up at my house, and after 3 bad sets I started posting about it not being a fix... a Band Aid at best...

I see guys claiming the guides are worn because of a 660 lift cam. Bull, because they are wearing on the stock cam as well; the LS7 is the least modded of all the LS engines, and those guys aren't wearing guides from big cams...

I see guys saying valve guides are a wear item. Again, Bull. These aren't tires or brakes. Valve guides should last 'til 100k miles. I no longer install valve guides on the LS7's for this reason, so I have nothing to gain here. The aftermarket heads are wearing as well. I run a half shaft rocker and have worn 4 sets of guides; the last guides I let Richard do and they're toast again....

The only thing I've done to fix the issue for me was to fully port an LS3 head set up and run it 9k miles. At 9k miles, everything was in spec. I lost 20hp from 5500 to 7000, but in all fairness, the LS3 heads I used still had the stock hollow intake valves an solid stem exhaust, so I could have got some of that back on a 2.200 intake valve being the intake for LS3 is 2.165. I have many videos i've posted to my youtube channel about this.

Some of you guys might not ever wear your reworked heads, just like some have been in spec after miles stock, but that is few and far between. These heads have big issues, guys, way more than the 1% crowd talked about. I've spent countless hours trying to figure this out. I've talked to hundreds of guys on the phone, etc. over the years to try to help as much as I could.

At this point I recommend running only the Moldstar-90 guides. Even if it's a band aid fix, it's better than what i'm seeing....

Originally Posted by john_g_46

Late last year I was contacted by the guy at GM that is responsible for all head manufacturing (I wish I could remember his name ... I'm gonna call him Bill). Four years ago we on the forum figured out that about 1/2 of the LS7s had a geometry problem. Bill verified that from 2006 to 2009 [Linamar] used two different [tooling setups] for final machining of LS7 heads. He knew about my tool and asked me to ship it to him, which I did.

Root cause ... still most likely not pedestal machining, but rather valve guide angle. In either case the result is that the rocker pallet "rolls" off of the edge of the valve stem. This results in high side forces in the guides.

Originally Posted by bjmsam

My heads are presumably from the good batch considering all valve-to-guide clearances measured within service limits at 62k miles, so when it comes time to have them refreshed (at 100k?), I certainly won't trade them for random cores...

Originally Posted by john_g_46

Good plan.

Originally Posted by Undy

Hmmm... at 88K miles E-V-E-R-Y single valve guide on my 07 Z was within GM's specs. This was 100% heads off verified by WCCH. They ALL are not bad.

Originally Posted by Mordeth

MS90 here. Just inspected after a hardcore year of tracking/racing the car, to the point of busting a ring land and having to pull the motor. Duty cycle and drive cycle were extreme, to the point of having to rebuild pretty much the entire motor - except the heads. Guides/valves still perfect. Zero movement. Zero play. Zero wear that I could detect personally. Inspected by machine shop during my engine rebuild and was asked if heads were magically re-built in the back of my truck on the way to the machine shop with my motor in tow.

Originally Posted by Hirohawa

I'm almost at 40K miles and just had my lifters replaced via warranty. Tech said everything else was in spec regarding this issue. So far so good.

Originally Posted by wantbluC6

If tens of thousands of miles of street race and long term ownership is your idea I wouldn't of bothered with a c6z. In retrospect. It's like having the fun of a supermodel GF with a bit of a drinking problem. So to speak. I know for how long I plan to keep my Z and the 2k miles or less I put on a year I'm not concerned.

I'm in the minority here. Ls3 maxed out heads from Chad are fine enough with zero guide worries. Ls7 aftermarket Chad mentioned were toasted after so many miles I forget. I suspect it to a degree comes a lot down to the Ti intakes just being too hard in general.. exhaust should be solid ss. Geometry was fixed with aftermarket but how many corrections can be made to justify the price of a set of fully ported aftermarket heads that as well cannot last 20k?? This can discussed ad naseum as it already has 8n dozens of threads the last 5 years or so. GM will forever deny anything wrong.

Originally Posted by rio95

Originally Posted by Innovate

Even aftermarket castings have issues? I have yet to see anything about that.

Originally Posted by Unreal

You can kill a guide on anything, stock or aftermarket. So yes everything has had failures but if you run a big nasty cam and a poor setup, it doesn't matter what you have.

One thing I don't see talked about often is running solid exhaust just for extra safety factor. Even if the do wear then the chance of losing a valve is crazy low as you are not going to pop off a valve head.

Originally Posted by Michael_D

This thread is reminiscent of the drama-filled threads that plagued this board four/five years ago. The only difference is the players, not the subject matter. Nothing has changed with respect to "guide wear". You guys are repeating the past. There is nothing magical about LS7 heads that suggests they follow new or different laws of physics or that they mandate an ignorance of theory.

There are only a few reasons for valve guides to wear. That's why I went through the effort to describe them, years ago, and I tried to use basic and simple to understand verbiage. https://www.corvetteforum.com/forums...uide-wear.html

There are reasons why "chad" was banned. Some were what landing him a spot on my ignore list, and that list is very small and exclusive.

Originally Posted by Michael_D

This thread is reminiscent of the drama-filled threads that plagued this board four/five years ago. The only difference is the players, not the subject matter. Nothing has changed with respect to "guide wear". You guys are repeating the past. There is nothing magical about LS7 heads that suggests they follow new or different laws of physics or that they mandate an ignorance of theory.

There are only a few reasons for valve guides to wear. That's why I went through the effort to describe them, years ago, and I tried to use basic and simple to understand verbiage. https://www.corvetteforum.com/forums...uide-wear.html

There are reasons why "chad" was banned. Some were what landing him a spot on my ignore list, and that list is very small and exclusive.

Originally Posted by Dirty Howie

I don't remember any drama

Not sure if you can read this


DH

Originally Posted by Undy

I remember someone and their GF keeping things stirred...

Originally Posted by Dirty Howie

I don't remember any drama

Not sure if you can read this


DH

Originally Posted by MTPZ06

“Good friend”?