Originally Posted by colton755
i want to know the max lift on a stock 1980 Chevy truck heads. and what i can do to make it hold more lift?
Something that has to be checked to be sure there's sufficient clearance between the top of the guide and whatever is between it and the bottom of the retainer. Then there is the spring which needs to maintain .050 inch when the valve is fully open between each and every coil. Then there is the slot clearance of the rockers to their studs again about .050 is as close as you can let this come. Then there is push rod to it's guide, increasing lift can run these into the ends of the guide, figure anything over .45 will require relief, tools are available from the hot rod sites for this mod. There there is sweep of the rocker end on the valve stem this needs to be centered as much as possible as the side load at high lifts eats the guides and stems letting a lot of oil into the combustion chambers and letting the valve roll around on the seat instead of closing things up.
For 1980 era smog heads lift beyond .5 inch is a waste of time as the port maxes out at that point and pushing for more lift doesn't net any flow improvement even when these old heads are ported.
Frankly by the time you try to change these sows ears for heads into a silk purse you'll spend as much money as anew set of modern heads like the Vortec would cost and those will deliver about 40 more horses out of the box over the best ported smoggers.