Im looking for that Vortec "specialist" out there on this one. I'm doing a carbed 327 conversion on my 95 Z and have run into what seems to be a problem/confusion. I have built the bottom-end of this motor forged for my high revving pleasures. I'm looking somewhere in the vicinity of 7000-7500 RPM's out of this thing. My problem is that I'm using Vortec castings #12252520 and from I've researched, these are 305 heads. Are these smaller runner design than the 350's? Also, these heads don't have the fast burn chambers... so what gives? Are these heads like a rare breed of Vortecs or what? Ive put over 900 dollars in the heads and now I'm afraid they wont be enough for the range RPM's. They've been fully ported so maybe that'll open em up a little. What are the specs on these suckers? Please help.

 

Vortec heads are not made for high RPM's. I know I have them, the 906 and 060 castings are the ones you want. Do you have 3 diamonds casted into the end of the head? I'm not too familiar with the 520's, but I can tell you they only made the vortec heads from 96-97 and they have 170cc runners and you have to use a vortec manifold.

 

The 305 vortec heads have very small valves. The (060 and 906) 350 heads have larger 1.94 and 1.50 inch valves and are the ones to use..

 

Ok I see some incorrect info.
Vortec heads were made from '95 to '98. The 1995's came in the 1996 trucks, 1998 came in the 1999 trucks.
There are two 350 vortec head numbers early ones are 906 and have a single hump on the ends. 062's are late model and service replacement and have the saw tooth marks on the ends.

You have the 305 vortec heads (I had a clean set of '97 castings at a swap meet 3 weeks ago for $150 and no one asked about them, I sold about 80% of the stuff I brought).

The differences, they don't have heart shaped combustion chambers, the combustion chambers are smaller, they have 1.84/1.50 valves. You can put big valves in but you need to unshroud them, there is a big space between the cylinders that will allow you to do this.

The intake runner size is close to the 350's, the only difference I see is the 305's have a little dam or something in the runner to increase swirl. The 350's have a vane centered on the valve stem.

I would remove this dam if I were to use the set I have.

I'm curious, how did you spend $900 on these?

 

I bought the heads for $350, then had almost $500 worth of machine work in them plus the valuable time of porting them (12 hours). So, the only major difference is the combustion chamber and the valve sizes? My intentions are atleast 400HP...Is this possible with these heads? Cam is about a .525 lift. I appreciate everybody's feedback.

 

I'd say you could get 400hp out of those.

 

The circle track guys are running the vortec heads alot when the rules require stock un ported heads and they are turning 7000 easy. I know of particular motor thats put up 600HP on an engine dyno. I will admitt that is was a kinda exotic motor with something like a 36-37 pound crank.. Might do a search with the circle track guys they might be able to shine more light on the subject for you.