if i upgrade the springs to handle more lift on my vette heads how much lift can they take before the valve guide to retainer becomes an issue, 550?

 

I'm pretty sure the clearance is around .480"-.490". Not much at all. You'll need to either machine the guide, install longer valves, or you might install smaller valve stem seals(K-Line).

 

You'll have to check it yourself. Everyone I talked to at other machine shops told me .490 was the max lift. There was quite obviously no work done to the top of the valve guides on the heads I picked up, and the valves, retainers and springs were all factory stuff... and yet I am running .517 lift on the exhaust side with enough clearance for .030 more lift. I would check it regardless, better to be safe than sorry.

 

The Vette heads were used on the ZZ3/ZZ4 engines which has a .510" exhaust lift and .474" intake lift. Differant springs were used on the ZZ3 and ZZ4 but the cam was the same.