Anyone have experience using the GM CNC ported LS3 heads?

It's kind of tough to find any kind of LS3 heads/cam setups at all! I was told by a very reputable shop that these heads are the best port job on a LS3 head they've tried/seen.

 

The problem with finding info on those heads on here is that heads are the last thing anyone changes on an LS3, because even the really good aftermarket heads will only gain about 20-25hp max over the stock LS3 heads (from all the dyno tests I've seen posted on the internet) with a mild to moderate cam on a stock cube LS3. Most guys on here simply go FI because that's much easier and then they can easily pick up 25hp from a pulley change.
The other thing is that most of the guys on here that have changed their heads are the big HP guys who go straight for the aftermarket, 6-bolt, exotica heads. And there are a lot of good heads out there for these LS motors nowadays. But most of those cost more than twice the coin of these heads and are overkill on a stock bottom end, IMHO.
To me, getting a good set of CNC GM heads that flow 350+ cfm for ~$1300 a pair is a no brainer, even if you only gain 25hp at the peak. I would love to see a test on those heads on a PD blower setup like mine, because the greatest improvement in flow is on the exhaust side, which means a lot on a FI setup.
I wish I had installed a set back when I did my blower install. Hell, at that price, I'll probably buy a set before they're gone, even if I keep them as trophies. I've also seen a write up somewhere that GM recently changed their CNC program and that a shop had tested these heads and they outflowed everyone else's CNC LS3 heads.
Couple of things to note if you're going to do a heads/cam build using those heads:
1. You will need to change at least the springs, using a good aftermarket ovate "Beehive" spring, matched to your cam specs, or go with something like a BTR spring and retainer kit, and;
2. Since these heads are ported and the intake to exhaust flow ratio is dramatically affected, you should get a cam that's spec'd to these heads rather than a stock unported LS3 head, which tends to need "help" on the exhaust side, which is why you'll typically see a large duration "split" between the intake and exhaust (like ~ 10*) on typical aftermarket LS3/L92 grinds.
I would bet you can easily get north of 500whp on a M6 C6 with a stock bottom end, using these heads and a decent sized cam.

 

I went with aftermarket heads instead of porting the OEM ls3 cause I won't accept a 280 cc intake port volume as very efficient on a stock block.

 

I love the answers. Thank you!

I THINK I am just going to get the ECS SC kit. I am looking for a shop to install it now. Trying to find the total cost before I take the plunge.

 

I hear you xBoostx, on the large port design. I remember all of the stuff I used to read by David Vizard and the late, great, John Lingefelter, etc., way back in the day, about port velocity making better torque etc. I put together many a combo for myself and friends based on that mantra.
And then I remember when GM first came out with the L92 head and I first read the specs - I thought it was a typo. I said, no way in hell that thing can even run properly!
But here's the thing: we're not talking about the need for good vacuum signal for carbed setups or flat tappet cams anymore either. It seems almost like the rules of physics have changed significantly. If someone had told me back in the late 80s / early 90s that one day we would have 376 cid street/pump gas motors putting out over 550 flywheel hp, I would've called them crazy.
I'm saying all of that to make the point that with the right camshaft, these heads will still make good power and are the best bang for the buck for a max effort N/A LS3.
Of course, something like the TFS 255 is a better head, but with a 12* vs 15* valve angle it's hard to say that their port design is what makes them flow so great and the fact that their more than double the price makes them much less of a bargain, IMHO. If I was going to spend that kind of coin, then I would just do a forged 416 and be done with it.

 

Hi man yeah I preffer to work with good parts and not compromise in this case for me was just a heads and cam if the block was to be consider would have been a 450 inch 4 inch stroke ls7 build I have in mind but waiting for the mid engine 2018 for now.

 

Unless you're gonna go with a high compression stroker, anything other than stock castings is money poorly spent. Yeah.....stock LS3 heads ARE that good.

IMHO, of course.

KW

 

Wrong post