skyhigh4by

iTrader: (1)

I am having conflicting information on how big of a cam can be used with vortec heads. I had planned on buying comp cams CS XE268H-14 lift of .479/.480. I was going to go with the complete kit that came with springs because I thought that was the issue with vortec heads??? Is it the actual casting that needs to be modified??? Will this kit work or do I need to do more? Also when I asked for opinions on my build I was advised to go with that 268 cam but now I find that there seem to be variations of it. The one I chose has an operating range 1800-5800 RPM with the stated .479/.480.....sound like the right one?

five7kid

iTrader: (14)

You need to remember that Vortec heads came on trucks. They weren't intended for high performance applications, they just happen to have good ports and chambers for high performance applications.

The guides are left fat inside the valve springs, which doesn't leave room for "good" springs, and the truck valve springs are junk for high lift and RPMs. The height of the guide is also an issue, reports are out there that only .440" valve travel exists on stock unmodified heads. Work-arounds are available, but the most sure-fire fix is to have the guides cut so you can use better valve springs and better valve stem seals.

Atilla the Fun

He's not far off, but I'm a professional automotive machinist. out-of-the-box Vortec heads can run a .470" cam, just the way they come. But the stock springs don't have the pressure for trying to run above 5000 rpm. With nothing more than a spring change, I have seen adequate clearance, with no machining by my shop, for .521" lift, but I only did it once. That engine ran for a full year before the guy decided to go to aluminum heads.

five7kid

iTrader: (14)

How much lift a particular head will support apparently has not been consistent over time. The .44" quote assumed a .060" safety clearance - so, the valve may travel .500" before the retainer hit the guide, but you should only allow .440" lift for that particular valve.

skyhigh4by

iTrader: (1)

Alright, I feel relatively safe with a max lift of .480 with matched springs. I'll just have to see what happens.

Atilla the Fun

GM used seals from more than one supplier, and the adjustments to their machining centers are made in a hurry. There are also variances in the retainers. Noone needs 0.060" clearance between the retainer and the seal, you need a 0.060" difference between max lift with your rocker ratio, and valvespring stacking.
You should always do a visual check for yourself before installing the valve covers. If you don't like what you see, it's cheap to get some "plus-0.050" locks, and then check your rocker to retainer clearance.