Originally Posted by Clayton A
Thanks guys, seems I have some work to do! It wouldn't be a project car if I didn't have things to tinker with right...
There's a chance that if the heads haven't given any indication of coil bind (broken springs, bent pushrods) or the valve stem seals being crushed out of existence by an insufficient valve spring installed height
(like the engine smoking, especially at start-up), that the heads may have had the necessary mods already made to them to accommodate more lift than the stock heads will allow. I would expect the valves to have floated very easily if they were stock Vortec springs w/that cam, too- one more reason to suspect the heads might not be totally stock.
But if the seals look to have contacted the retainers or there are any other indications there's not enough clearance at max lift, there are several routes you can take to safely use more lift than the about 0.450" lift that the stock Vortec heads can handle in stock form. Read the info here
for more. Another thread w/info on the Vortec head (thread has 59 pages!) is here
But the bottom line is you may want to have the guide bosses turned down for aftermarket valve stem seals and shortened at the same time to let you use springs that will allow for more lift than the stock springs.
Be sure to check the clearances
of the various points in the valve train when you mock up the assembly before final assembly. Better to find a problem before
it causes damage!
Don't overlook using a tight quench distance
to your advantage. A correct quench will help prevent detonation. This means you will want to measure how far down the cylinder the pistons are at TDC. This can vary due to how much the deck may have been milled as well as the compression height (CH) of the pistons. Some "rebuilder" pistons have a 1.54" CH instead of the factory 1.56" CH- this can cause the quench to be too wide unless corrected.
This barely scratches the surface but will give you a start.