Limits of Vortec Heads

[SHOTROD81]

Hello! After finding a broken rocker arm on my SBC (with help from many of you), I have new Comp Cams 1604 rockers ready to be installed after I remove the intake to inspect the lifter. After doing a little reading online, though, I am a little concerned that these heads may be problematic even after fixing the rocker issue. Does anyone have experience or opinions on how much is too much for iron Vortec heads? When I compare the cam specs to the limits I have read about for Vortecs, it seems that someone may have pushed these heads a little too far. Since I do not know who did the heads on this motor, I don't have any part numbers or data to show, but I do have the cam sheet shown below. If done right, does this head/cam combo seem viable or am I asking for more problems? In case it generates any more discussion, I attached a few pictures of the current heads to show some of what seems to be a stressed valvetrain. If you look closely, the right side of each rocker has a little deformation behind the roller, many of the rockers are marred on their tops, and one appears to have a sunken area over the roller, as shown by the arrows. Any input on any of this would be greatly appreciated!


BULLET CAMS
8785 Old Craft Rd
Olive Branch, MS 38654
662-893-5670
Grind Number CHS 295/306-07R CHEVROLET 350-400
Part Number 501000 SN S59515
Intake Exhaust
Duration at .050 262 272
Lobe Lift .4120 .4190
Separation 107. OP CL OP CL
Timing Events @.050 28 54 67 25
Duration @.020 295 306
Gross Valve lift .618 .628
Rocker Ratio 1.5 1.5
Valve Lash .024 .020
Degree Intake Lobe to 103

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[Honky Kong jr]

Looks like they were walking on the valve tip, and hitting the valve cover. Unless work was done to the valve spring seat or longer valves installed the lift on that cam far exceeds a stock Vortec head. This will create serious coil bind and valve train damage if no machine work or valve replacement was done.

 

[crazy4offroad]

Around 0.460 is the max valve lift for stock Vortec heads. More than likely yours have been machined in the spring seat and valve guide for more lift, otherwise it would have been catastrophic failure long before now.

 

[MikeB]

That's a radical cam you have there. Typically it would be used with 12:1 compression or more, racing heads with 225cc or bigger intake runners, single plane intake, 1-3/4" headers, all in a light car with 4.56-5.xx gears. I mean, it's a racing cam probably designed for a 4500-7500 RPM powerband.

If you must keep that cam, no way would I even consider standard GM Vortec heads (casting nos. 906 and 062). The beauty of Vortecs is high flow at low-mid lift and low-mid RPM, which made those 96-up 1/2 tons truck haul ass -- even with a heavy load. That's not to say they can't be modified by a pro to support over 500hp, but it's very expensive.

Regarding valve lift, even the GM Performance Bowtie Vortec heads (both small and large ports versions) have a max lift of .530" out of the box. How did you modify yours to work with more than .600" lift?

Old article, but still valid information:
http://www.onedirt.com/tech-stories/engine/a-guide-to-vortec-vs-oe-small-block-chevy-heads/

 

[MikeB]

Just noticed that you are not using self-aligning rocker arms, but instead guide plates that obviously aren't designed for Vortec head valve placement. Instead you should dump the guide plates and use rocker arms with roller tips like these:

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[gpmorgan]

I don't think those dual valve springs would fit the spring pockets if they weren't machined. I would check for coil bind. It's been a while but I think you need at least 60k between the coils when full lift is achieved. As stated, those vortec heads need quite a bit of machine work when using a cam that size.

 

[Honky Kong jr]

I don't think those dual valve springs would fit the spring pockets if they weren't machined. I would check for coil bind. It's been a while but I think you need at least 60k between the coils when full lift is achieved. As stated, those vortec heads need quite a bit of machine work when using a cam that size.

Hey could bind makes for a built in rev limiter lmao oh **** wait I think he is running solid lifters scratch that for hydraulic lifters it does not solids

 

[gpmorgan]

Hey could bind makes for a built in rev limiter lmao oh **** wait I think he is running solid lifters scratch that for hydraulic lifters it does not solids

Yeah, you need a rev limit with that solid roller. Lol

 

[Honky Kong jr]

Yeah, you need a rev limit with that solid roller. Lol

Or reinforced valve covers and hood for when stuff wants to cole out and look around. But then again depending on ignition system it might not rev to its potential anyway.

 

[gpmorgan]

If you don't have a coil bind issue, I would make sure the valve geometry is correct. After checking, spin the engine by hand, about a quarter turn at a time, and inspect each rocker for contact with the castings.

 

[gpmorgan]

To check valve geometry you need to mark the valve tip and install the rocker . Spin the engine over . Remove rocker and look at where the roller is moving on top of the valve. It needs to stay in the center on the valve tip as much as possible. To adjust you will need get an adjustable push rod to determine what length push rods you need. As I mentioned in the other thread, comps web site has a better explanation of the process than I can explain.

 

[SHOTROD81]

That's a radical cam you have there. Typically it would be used with 12:1 compression or more, racing heads with 225cc or bigger intake runners, single plane intake, 1-3/4" headers, all in a light car with 4.56-5.xx gears. I mean, it's a racing cam probably designed for a 4500-7500 RPM powerband.

If you must keep that cam, no way would I even consider standard GM Vortec heads (casting nos. 906 and 062). The beauty of Vortecs is high flow at low-mid lift and low-mid RPM, which made those 96-up 1/2 tons truck haul ass -- even with a heavy load. That's not to say they can't be modified by a pro to support over 500hp, but it's very expensive.

Regarding valve lift, even the GM Performance Bowtie Vortec heads (both small and large ports versions) have a max lift of .530" out of the box. How did you modify yours to work with more than .600" lift?

Old article, but still valid information:
http://www.onedirt.com/tech-stories/engine/a-guide-to-vortec-vs-oe-small-block-chevy-heads/

I didn't modify them, I bought the whole package as-is, with about 1000 miles on the rebuild. The motor was built by a local builder called NVR Racing in Butler, Wisconsin. They have been very helpful, including a complimentary house call to make sure the valve lash was set correct this spring. They did not modify the heads though, they were provided by the previous owner when the engine was built. I can only assume they checked the heads for viability prior to the dyno runs. I was looking for a solid C10 with a fairly fresh plant for a little fun and for hauling. Had it a year now and I am getting a serious education in the trials and tribulations of having a motor that is a little more radical than I anticipated. Thanks to you guys and a couple of builder/racer friends, I am going at this with a lot of help.

 

[gpmorgan]

I'm sure if it was built by a reputable builder, they would know if the parts were compatible. The things I mentioned should have been checked. Put those new rockers on and give it hell.

 

[Honky Kong jr]

I'm sure if it was built by a reputable builder, they would know if the parts were compatible. The things I mentioned should have been checked. Put those new rockers on and give it hell.

Then again they ran it with guide plates and not self aligning rockers that hit the valve covers and retainers....just saying...

 

[gpmorgan]

Yeah that's true. Not sure it would need the self aligners with the heads set up for that cam though. But there's no excuse for the short valve covers, unless there are no tall covers available for the center bolt style. I personally wouldn't use that style head for performance, so I don't know what's available for them.