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Old 09-18-2010, 08:42 AM
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vortec heads 1.5 or 1.6 rocker

Gents, I'm still trying to learn here.

Just picked up a set of rebuilt Vortec heads with upgraded Comp Cam 5.25 lift springs, stock 1.94 valves, casting #10239906 for $350 on craigslist.

Should I use 1.5 or 1.6 rockers and any suggestion on brand/part#? Don't want to spend a fortune though. What kind of HP/TQ improvement would I see with 1.6 rockers?

Can I use the stock push rods or do I need to get small rods? Recommendation on brand/part#?

My 350ci hydrylic cam spec's are:
Cam lift .310/.310
Valve lift .465/.465
Lobe ctrs 107 int./117 exh.
Adv dur. 290/290
.050 dur. 224/224

I believe the Vortec CFM flow numbers stay level/level off between .450 lift and .500 lift. My cam is a .465 lift so I am right between .450 and .500; therefore, I don't think I'll see much if any gain with the 1.6 rockers since the 1.6 rockers should take me from a .465 to .495 lift? Will the high lift hurt my botton end with this cam? I know alot of questions but I'm trying to determine the ramifications from going to a 1.6 and may have my analysis wrong. Any thoughts?

I hope my cam response well with these vortec heads, if anyone has a similiar cam let me know if you were happy with results. Appreciate any advise.

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Old 09-18-2010, 11:29 AM
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Vortec heads come w/self aligning rocker arms. They won't allow a valve lift of more than about 0.450"-0.470" w/o the stock retainer hitting the valve stem seal, unless the guide boss is shortened or the retainers changed or the stock retainers modified, possibly w/a different seal as well.

Because they use SA rockers, the slot usually present in the head that guides the pushrod (and thus aligns the rocker) isn't used. This means either SA rockers OR guide plates- but never BOTH- have to be used.

So, unless the guide boss has been trimmed to allow for more lift, the cam you now have is already at the limit of lift- if not past it- using 1.5 rockers.

I'm not sure what you mean by "small rods". The correct pushrod length is determined by achieving the correct geometry of the valvetrain during the engine mock up by using a length checker like made by Comp or an adjustable pushrod.

You can use the stock OD for the p-rod, but I would suggest you use a thicker wall- like 0.080". If you use guide plates, the p-rods have to be hardened.

A lot of info on Vortec heads and mods to them, etc. is HERE.
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Old 09-18-2010, 05:32 PM
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The stock Vortec valve springs don't use a damper. They made some castings that don't need the guide boss machined down. I didn't end up with them. These heads need the guide boss trimmed.
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Old 09-19-2010, 04:29 PM
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Quote:
Originally Posted by cobalt327
Vortec heads come w/self aligning rocker arms. They won't allow a valve lift of more than about 0.450"-0.470" w/o the stock retainer hitting the valve stem seal, unless the guide boss is shortened or the retainers changed or the stock retainers modified, possibly w/a different seal as well.

Because they use SA rockers, the slot usually present in the head that guides the pushrod (and thus aligns the rocker) isn't used. This means either SA rockers OR guide plates- but never BOTH- have to be used.

So, unless the guide boss has been trimmed to allow for more lift, the cam you now have is already at the limit of lift- if not past it- using 1.5 rockers.

I'm not sure what you mean by "small rods". The correct pushrod length is determined by achieving the correct geometry of the valvetrain during the engine mock up by using a length checker like made by Comp or an adjustable pushrod.

You can use the stock OD for the p-rod, but I would suggest you use a thicker wall- like 0.080". If you use guide plates, the p-rods have to be hardened.

A lot of info on Vortec heads and mods to them, etc. is HERE.
Thanks for the vortec link, it has alot of excellent vortec info. I meant to say push rods. The guide boss has been trimmed down for more lift. I was just trying to determine if I should go with 1.5 or 1.6 rockers given I already have a .465 lift cam and I hear the cfm flow on vortec heads is fairly flat betweeen .450 to .500 so thought I might not gain that much going with the 1.6.
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Old 09-19-2010, 04:54 PM
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Quote:
Originally Posted by Hanks56Chevy
Thanks for the vortec link, it has alot of excellent vortec info. I meant to say push rods. The guide boss has been trimmed down for more lift. I was just trying to determine if I should go with 1.5 or 1.6 rockers given I already have a .465 lift cam and I hear the cfm flow on vortec heads is fairly flat betweeen .450 to .500 so thought I might not gain that much going with the 1.6.
I prefer to use 1.5 ratio rockers with a cam that has the specs desired, using that ratio. There are valid reasons to use 1.6 ratio rockers, but that concerns using the OEM roller block- whose lifters are retained by a dogbone that can lose contact w/the roller lifter if the base circle of the cam is too small.

There can also be performance gains- in the right application- by going past the point of most flow, lift-wise.

This concerns the amount of flow under the curve. The idea being, you go a bit past max flow, because the valve sees max flow on both sides of the lobe, opening and closing.

In your case, the amount of lift and duration of the cam you cited are fine for most applications using a stock, unported port, IMO.

Use every trick in the book to keep the cam lobes alive during break in. I don't know the required spring specs for the cam you mentioned, but those springs you have on the heads now sound like they could have fairly stiff specs on them.
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Old 09-19-2010, 05:08 PM
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I think the stock Vortec springs are rated at 80 lbs. The spring in the picture with the stripe is a Z28 spring rated at 110 lbs. You can find Vortec heads that are good deals but if you start dumping money into them they are not such a deal anymore. You have to buy the intake manifold also. I see aluminum SBC heads at swap meets in the $400 range.
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Old 09-19-2010, 05:25 PM
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This is a spring from a AFR head on the Vortec head. You can see it dwarfs the stock Vortec spring.
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Old 09-19-2010, 05:28 PM
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This is a cam card from a Crane cam. It has the recomended spring pressure listed.
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