ive stumbled upon a post on craigslist for a set of vortec heads with 64cc combustion chambers. i believe the casting number is 10239906. which is a 96 and up truck head from a 350. comes with stock 1.94/1.55 valves. now my question is, ive seen alot of people say they cant take alot of lift. someone said specifically anything over .440 lift. and i know my cams specs are as following. Duration at 50 inch lift 230 int./236 exh. valve lift with factory rocker arm ratio. .487int/.490 exh. and a 110 LSA so back to my question. i plan on going to bigger valves with these heads, and doing all the machine work myself. will these fit with no modifications? other than larger valves , aftermarket springs, and 1.6 ratio roller rockers? or will i have to mill the head or make the valve seat area larger? thanks also some info about the engine. its an early 80's 350 block bored .040 over, scat stroker kit, internally balanced, keith black forged pistons, comp camshaft, and going with an edelbrock rpm intake and edelbrock carb.

This should help you.
http://www.chevyhiperformance.com/ho...458/index.html

I have vortec heads (906)on my 400 setup.I had mine done up from the start.

2.02 1.64 valves, screw in rocker studs, pushrod guide plates and I told the guy I was going to run a 600 lift roller cam (which I'm not).

I'm running 496/496 lift w/ 1.6 roller rockers. I converted the block to gm style roller setup. never had a problem. If you do the math it is 529.06 lift.

The only problem I have had was rocker studs were breaking, I fixed that by buying longer ones. It seems the rocker nuts were not grabing enough of the stud.

I also ported and polished my heads (mild).

the problem with trying to run more lift is that the valve guides are too tall and the valve retainers hit the guide when you open the valve past about .450. Have the valve guides cut down and the spring seat opened up and you'll be good to go. Also, a little porting on the exhaust side of these heads goes a long way.

Check out the Chevy Hi Performance link good stuff.

i just read the article and it said to avoid the casting number that i plan on using which is 39906. because of hardened exhaust seats. is there any way i can get around this?

There is nothing wrong with the 906 castings. That statement was later retracted.

like he said there is nothing wrong with them. In early 2000 the word was the 906 were not as prone to cracking as other. You either love the heads or hate them.

You can make these heads take more lift without having to machine them. Get a set of yellow Z06 springs with retainers and they bolt right in. They are a beehive style spring and you can get them on ebay for like $70 a set. IIRC it makes them good to over .550 lift.

ive heard good stuff about using the LS top end goodies like springs and retainers and whatnot. but i feel abit iffy about using used stuff. are those yellow z06 springs alot better than say an aftermarket brand?

The ones you can get on ebay are brand new. just look up "Z06 Valve springs" and you will come up with quite abit. Or you can look up part number 12499224. That will give you the whole set of 16 springs.

From what i've been able to tell, the hardened exhaust seat just had a 1-angle valve job from the factory. If you get a used set of heads, you'll want to get proper 3-angle valve jobs done anyway, and that means that stock 1-angle valve job no longer matters anyway. They'll flow the same after that.

GM used them on their crate engines.