What is the most duration and lift could run on stock vortec heads moded to take more lift Before the heads would them self would cause restriction?
I was thinking of runing 230 to 238 maybe even up to 240 some thing on the exhaust side.
How big can you go?
I have a 700R4 and 3.23 gears but I will change them along with the torque converter.

 

Well, as far as duration goes, it's really a matter of how much motor you have under the heads.

A smaller motor will reach the peak flow of the heads at a higher speed, and therefore would probably require a cam with more duration. If you look at extremes, something like a 427 SBC would reach peak power much earlier in its rev range and would require a comparitively smaller cam than, say, a hot 283 with the exact same heads (I'm neglecting the effect of the bore diameter on valve sizing and port flow for the purposes of this discussion).

So, bottom line - there's no absolute limit on duration. Putting a big-displacement motor under stock Vortecs and then going wild with cam duration might be a little disappointing, though.

Now, lift - that's a different story. There's the issue of mechanical limits due to retainer/seal interference, the possibility of contact between the pushrods and head with 1.6:1 rockers and high-lift cams (an issue with some iron LT1 heads - I don't know if Vortecs suffer from the same problem), and then the limit of the valve springs - both from a coil-bind standpoint and from a lack of seat pressure. Your best choice here is simply to throw away the stock springs and have a machine shop rework the spring seats and guides. You should be able to accommodate .550+" of lift with these simple mods and a good set of springs.

 

i am running the performer rpm cam with 1.6 rockers i just got these springs so that i didn't have to machine the heads

http://store.summitracing.com/partdetail.asp?part=26217


justin

 

You mentioned p rod and head interfearence on vortecs, Yes it does happen.
The moded heads I was looking at were cleared up to .580'' but were not ground out to prevent push rod scuffing.
The bottem end was going to be a stroked 350 (to 383 or 396).