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Old 03-07-2012, 12:35 PM
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Valve train build

I need some advice with my plan of building my valve train. (budget build. Not going to drag race, just a powerful cruiser). I'm going to use a stock bottom end '73 sbc 350. I just bought some '96 906 vortec heads. I'd like to beef up the heads and cam. Would this combination work?

Cam http://www.summitracing.com/parts/SUM-K00072/
Spring Set http://www.summitracing.com/parts/SUM-174001/
1.6 self aligning full roller rockers http://www.summitracing.com/parts/PRO-66915/

Also, the stock press in studs are supposed to be good to 220 pounds. How can I tell if this setup will be above or below that, before screw in studs are needed?

Lastly, is there a way to know if the valve to valve guide clearance will be ok for this setup without putting it all together? Or do you think this setup should be fine if the current clearance is good?

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Old 03-07-2012, 02:52 PM
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The cam lift limits are generally said to be about .450" on Vortecs. There are different retainers and springs available that can increase that limit. Using 1.6 rockers only increases the chance of bind.

As far as pressed in studs, I wouldn't trust them with 357# springs. Easy enough to pin them or pull them out, tap and install screw in studs.
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Old 03-07-2012, 03:24 PM
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As 68 says, also you're doing the right thing by asking questions, do your research before buying anything. Scroggins-Dickey sells the high performance Vortec heads and could probably answer most of them. By all means, if you use stock heads use screw in rocker studs and forget about them.
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Old 03-07-2012, 04:32 PM
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Great, thank you for the response. That spring set has .490 max lift and that cam needs .480 lift on a stock rocker. Is this too close for comfort when combined with the 1.6 rockers?

I just read, in a chevy max performance book, that the stock guides are good for anything under .5 inch lift. So I should be good there.
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Old 03-07-2012, 06:33 PM
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Most small block cams are "measured" using 1.5:1 rockers. If you change to 1.6s, your theorhetical lift will increase to .512".

It's ALWAYS a good idea to install screw-in studs and guide plates. "Rail" rockers are okay, but the complete "package" is more stable. "Pinning" is "old school", and works, but it also renders the head nearly useless if you break a stud. Very difficult to machine "out" (the rolled pin used) and still have enough stud boss to work with. If you "catch the fever" and desire future "expansion", the screw-in studs will already be there.

Bronze guides are used for higher lifts because they resist wear under more "side loads" caused by the valve action. Agreed, .500" is the "rule of thumb" for bronze. Avoid the temptation to have "liners" installed, and hold out for real .502" OD bronze guides. We use SBI 340-1033BR.

The Vortec head flows pretty well "as cast". The exhaust seat benefits greatly from a "three angle" (or radius) cut, out near the "edge" of the valve face. The factory seat is pretty "sharp", and near the top of the face.

FWIW

Jim
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Old 03-07-2012, 08:46 PM
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Thanks for the tips Jim. Just curious, how did you come up with the .512?

I'd like to keep the stock guides. Does it matter whether I switch to 1.5 ratio rockers or a smaller cam to keep the lift below .5?
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Old 03-08-2012, 06:59 AM
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"Advertised" or "theorhetical" lift is .480". Divide that by the 1.5 rocker ratio to get "lobe" lift. Multiply lobe lift by 1.6. Viola!! In conventional V8s, "valve lift" is always a product of the lobe lift x rocker ratio.

NOTE: Hydraulic tappets are always listed with "theorhetical" lift because of the "shock absorber" function of the lifter, which can make actual lift a little lower. Hydraulics also tend to be a little less "consistent" where valve train movement is concerned. Cams using "solid" lifters are listed with "actual" lift.

I've seen heads with stock guides work fine for such applications. I've also seen them wipe a guide out toot-sweet. It costs about $175 for a set of guides "installed" (here, prices vary from one shop to another).

Jim
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Old 03-08-2012, 07:44 AM
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I see, good to know. I may go with this setup (or something similar) and hope the stock guides work. Looks like I may need springs for a .512 lift tho. maybe these http://www.summitracing.com/parts/SUM-174000/

I guess I have one more question about pushrods. Do I need to purchase an adjustable pushrod to figure out exactly what length I need? Or can I figure it out mathematically or some other way? Or will the stock ones work?
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Old 03-08-2012, 05:14 PM
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Yes, those springs should work fine. Be sure to check seal-to-retainer clearance at "max lift". Also, make sure to measure "installed height" (the distance between the spring perch and the bottom of the retainer with the valve fully closed). If it really is 1.75", it's a "drop in" deal. If less, it can be a problem if not corrected.

Jim
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