MYCoupe

Anybody running the Chevrolet Performance CNC ported LS9 heads? The part number is 19328743. Was thinking of using them with BTR Ti retainers and PSI 1511ML springs. One of the things I like is the nice bump in compression right out of the box without having to mill them due to smaller combustion chamber. Undecided on what cam to run yet. These would be for a manual LS3 2012 GS.

CI GS

I was considering those too, because they looked like a hell of a deal, but then I read a few posts about the titanium intake valves wearing out the guides prematurely. I also read that the valves need to have the stems polished or some such thing, to cure that problem. I also could not find any information that could confirm that they have the same CNC program as the CNCd LS3 Head.
In the end, I just bought the CNC LS3 heads and saved like $200-300 bucks, IIRC. The LS9 heads are one hell of a deal regardless, because they are made from a higher grade alloy than the regular GM heads.

xBoostx

If you are going to use LS3 CNC GM head use only for N-A application not with boost we have had many problems with the LS3 CNC head blowing away a path over the gasket 30 40 thous deep and 10mm wide off the head aluminum something we have not seen any head do before.

We mill down the head flat again and again it blew off aluminum and started a huge leak, it can be mill flat again but it will have too much compression for boosted use and no warranty is not going to do the same again.

CI GS

The LS9 is a better casting, but the LS3 CNC Head is the same casting as the stock LS3 heads, and they’ve been tested to 950+ whp under boost without failing.

MYCoupe

Yeah, like you I have heard some conflicting info regarding the valve guides wearing prematurely with the Ti intake valves. However, I have not heard of any factory ZR1s really having that issue. As for the CNC job I do believe they are the same as the regular LS3 heads, but again hard to get definite confirmation. There was just great deal on a set on eBay, but I didn't pull the trigger on them.

xBoostx

You be the jodge...
I don't see this happening with production ls3 heads.

old motorhead

Damn, that's ugly. Wonder why the CNC'd LS3 head is weaker than the stock LS3 head in that area. There's a jillion stock long block LS3's that have been making good boosted power for lots of miles.

CI GS

Yeah, That's is ugly. But I cant see HOW the CNC LS3 head could possibly be weaker/softer etc. than the stock head, particularly in that area, since its the exact same exact casting, and especially bearing in mind that there's no difference in machining of the combustion chamber side of the two heads. That simply makes no sense to me. Blaming that mess on the CNC machining process of the inside of the ports is a hell of a stretch.

xBoostx

I will say this will use any production ls3 head but not the ones sold outside production warranty.
Cnc has nothing to do with the quality observed in these castings imo.

Happen two times not just ones.

We bought and use our share and I'm giving the OP my feedback cause he asked about the ls9 just a fair warning about the LS3 casting that all.

MYCoupe

Well I don't plan to run any boost (or nitrous), but point taken. In any case the LS9 heads are stronger than the LS3 heads so I can't see the CNC porting them weakening them to the point of failure in a N/A application.

handyandy1496

The GMPP ported ls3 head is just that. They have the same casting number. Same material. People everywhere are just trying to put too much boost to the STOCK head. That is why GM makes an ls9 head. For blower application! It has a thicker deck and an extra bolt hole for extra clamping force and titanium valves. Its very easy to blow holes in aluminum during prolonged detonation and fi. Some guys will polish all the valves because of roomers and probably won't even chamfer all the edges in the combustion chambers and pistons or deck the block! Or find a superior gasket.
I run GMPP ls3 heads on my 418 11.7/1 Ls2 on 93 oct. I use a .035 gasket on a .030 over block. For $1250.00 I got 20 more rwhp throughout most of the rpm band at least all the rpm that I use with a 3800 yank to 7200 rpm. It's an excellent bang fort the buck. Plug and play for any N/A lsx. You will never see anyone praise them because the guys who build race/street engines cant make any extra labor money on them. I don't need marked (3x) up Trick Flows that have there own problem's that builders don't want to talk about. Or a $2000 auto cad program on a ls3 head that MIGHT make a couple of more pony's. There fine with a 200 shot of nitrous as well. It's all in the prep and known limitations.

CI GS

Yeah, there are lots of folks using the LS3 CNC castings on blower applications, especially in the PD Camaro community, who make way more boost and power than I can ever make on my pulley-limited C6 blower setup, without any issue. I’ve read articles by folks like Tony Mamo who tout these heads for PD blower applications. Obviously, if you want to crank out over 1000whp and/or 18+psi of boost, then LSA, LS9 or aftermarket castings are a better choice. But forgive me if I’m skeptical of a couple of photos that show some very strange unusual damage, primarily around the bolt holes and the water jacket area of the head, being presented of evidence of weakness of the CNC casting, which is the exact same casting as the stock LS3 Head. I have no idea what caused that blow-torch looking damage, but I’ll bet a big chunk of money that it has nothing to do with CNC porting a stock head.