linkz761

would i have any trouble running this cam CCA-12-212-2, (.05 duration 230, 480 lift) with stock vortec heads??? I have access to better springs if that is the issue. I just havent been able to find a straight answer to why the vortec heads cant run bigger cams... Thanks.
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Also, if anyone could tell me what my comp. ratio would be with stock pistons and the vortec heads, that would be awesome!

RFmaster

LinkZ



The most troubling part of the Vortec head installation is the limitation of the valve lift. A '95-and-earlier head has the valve lift limited by the distance between the valvespring retainer and the valveguide when the valve is at its maximum lift. The Vortec head has the same valvespring retainer to valveguide clearance, but also has a valveguide seal installed between the retainer and the valveguide. The valveguide seal will be pinched between the retainer and guide if valve lift exceeds 0.420 inches.


The '95-and-earlier heads use a tin shield over the spring that keeps excess oil from running into the valveguide and an O-ring installed on the valve stem that keeps oil from running down the valve stem and into the guide. The tin shield and O-ring allow up to 0.500 inches of valve lift.


//RF

linkz761

Ok, thanks for the reply. Now, my next question is what needs to be done to get the heads able to run over .475? And how much will it cost me at a machine shop???

Atilla the Fun

I'm just what you asked for, a professional automotive machinist. out-of-the-box Vortec heads can run .470" lift with no machine work, but the stock springs lack pressure for running over 5000 rpm. With just a spring change, and no machine work by our shop, we've run .521" lift, but we only did it once. It ran a full year that way, before the guy decided to go to aluminum heads.

linkz761

Ok thats sounds great, I have the springs to run a bigger cam. Now my only other questions is... Is the problem with running a bigger cam a "metal on metal" issue, or is it a flow issue?? While I am ok with getting a little less flow than should be from a cam, i would like to ttry to avoid erring on the metal munching side.

Thanks!

Atilla the Fun

okay, I've had plenty of vortec heads on the flow bench, and there's good reason to limit your intake lift to 480 advertised, and use 1.5:1 rockers. These intake ports actually flow less air, every time, at 0.500" valve lift than at 0.475".
Every time you play with the valvetrain, no matter what you've been told, you need to double check your retainer to seal clearance for yourself. To do this, assemble everything, except leave the valve covers off. Get some good lighting, and peek inside the valvesprings as you slowly turn the crank.
GM used seals from different suppliers, and there are likewise variations in the retainers.
If you get springs that have over 110 psi at 1.75", you can use "plus-0.050" valve locks, but then you hafta check rocker to retainer clearance, but this can save you from machine work.

Hog

Or run the Crane springs, or the Comp Cams Beehive springs with 787-16 retainers. these springs will drop in.

peace
Hog

Stephen

iTrader: (12)

Yes.....Those allow higher lift. But with stock chamber & port flows, your still choked on the flow of the incoming air. With proper porting, you can make use of the increased flow made possible by those beehive springs.

Hog

yes the Vortec port stalls at around .500" lift but theres no reason to not use a 0.525" lift cam. Doing so actually allows the valve to be in the high flow lift range of the valve cycle.
Instead of the valve being at .500" lift once, it is actually there twice, more air will flow with a 0.525" cam than a .500" cam even though the port stalls at .500".

I'm not sure what you mean about the stock chamber limiting port flow however.

Limiting lift to .480" will surely leave power on the table. using these springs allows for more flow/power.
You dont need to port the heads to take advantage of more lift on the Vortecs, but it does help power of course, esp when you attack the exhausts.
I just clean up the intakes, dont try and reinvent the wheel on the intakes, you'll kill their excellent low lift qualities.
Better off to start with a Bowtie Vortec iron head.

Hog

skinny z

Vortec heads w/ XR276HR Comp cam and 1.6 rockers give 536"/.544" lift values.
Push rod holes elongated and drop in Beehive springs. OEM valve seals.
No problems.