Going with 906 Vortec heads on my 350, have a couple of questions - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-23-2010, 04:50 PM
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Going with 906 Vortec heads on my 350, have a couple of questions

After reading on here and doing some homework I have decided to abandon porting my 434 heads and I ordered a set of rebuilt 906 Vortec heads.

Can anyone tell me the valve spring pressure and safe lift on them and if I need diffrent springs/retainers?

I am going to run this Lunati Bare Bones cam

Cam Style Hydraulic flat tappet
Basic Operating RPM Range 1,500-5,500
Intake Duration at 050 inch Lift 214
Exhaust Duration at 050 inch Lift 224
Duration at 050 inch Lift 214 int./224 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.443 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.465 in.
Valve Lift with Factory Rocker Arm Ratio 0.443 int./0.465 exh. lift

Thank you,
Johnny

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Old 04-23-2010, 05:50 PM
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You should always use the springs that match the cam. Not doing so leaves alot of power on the table. You said the heads are rebuilt, have the valve guides been clearenced?
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Old 04-23-2010, 08:57 PM
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Quote:
Originally Posted by DoubleVision
You should always use the springs that match the cam. Not doing so leaves alot of power on the table. You said the heads are rebuilt, have the valve guides been clearenced?
I agree and will change the springs if needed. I haven't received the heads yet, they are in shipping now. My cam card calls for 108 spring pressure on the seat. I was looking at this ebay kit
http://cgi.ebay.com/ebaymotors/VALVE...item563abfa970
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Old 04-23-2010, 09:26 PM
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I`m not too sure I`d trust the ebay kit. "Alex`s private brand" sounds kind of spooky to me. I always use the springs the cam company recommends, but that`s just me. I asked about the guide clearance as if they aren`t contact will occur which will do it`s share of damage. I think the lift limit of Vortec heads are .460
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Old 04-23-2010, 11:15 PM
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Although you want enough seat pressure to keep the valve from bouncing repeatedly, what you really should be concerned about with a flat tappet cam is the over-the-nose pressure. Since the oil companies took all the EP lubes out of oils, it has been a nightmare keeping flat tappet lifters and cam lobes in one piece. In this case, you're looking at 110 on the seat. The rate on those springs is 348 lbs per inch, so if you multiply your highest valve lift (0.465) times the rate, you will find out how much additional pressure will be exerted on the cam with the valve open. 348 times .465 = 162 lbs. Add 110 to 162 and you find an over the nose pressure of 272 lbs. This is well within my personal limit of 290 lbs. I don't use flat tappet cams any more, but when I did, I wouldn't recommend more than 290 lbs over the nose after the oil debacle. If the motor won't rev to where you want it to with 290 lbs, change to a roller cam.

At any rate, use some kind of EP lube in the engine oil and pay close attention to break-in suggestions.

Scoggin-Dickey offers a spring kit for the Vortec heads. Part number KITSD1004 will get you 16 springs, 16 retainers and 32 locks for $66.98. SD1004 springs (known in some circles as Z-28 springs) are rated as follows:
Closed pressure 100 @1.735"
Open pressure 285 @1.210"
Coil bind 1.160"
Max lift 0.525"
www.sdparts.com

Last edited by techinspector1; 04-23-2010 at 11:23 PM.
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Old 04-24-2010, 09:37 AM
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Quote:
Originally Posted by techinspector1
Although you want enough seat pressure to keep the valve from bouncing repeatedly, what you really should be concerned about with a flat tappet cam is the over-the-nose pressure. Since the oil companies took all the EP lubes out of oils, it has been a nightmare keeping flat tappet lifters and cam lobes in one piece. In this case, you're looking at 110 on the seat. The rate on those springs is 348 lbs per inch, so if you multiply your highest valve lift (0.465) times the rate, you will find out how much additional pressure will be exerted on the cam with the valve open. 348 times .465 = 162 lbs. Add 110 to 162 and you find an over the nose pressure of 272 lbs. This is well within my personal limit of 290 lbs. I don't use flat tappet cams any more, but when I did, I wouldn't recommend more than 290 lbs over the nose after the oil debacle. If the motor won't rev to where you want it to with 290 lbs, change to a roller cam.

At any rate, use some kind of EP lube in the engine oil and pay close attention to break-in suggestions.

Scoggin-Dickey offers a spring kit for the Vortec heads. Part number KITSD1004 will get you 16 springs, 16 retainers and 32 locks for $66.98. SD1004 springs (known in some circles as Z-28 springs) are rated as follows:
Closed pressure 100 @1.735"
Open pressure 285 @1.210"
Coil bind 1.160"
Max lift 0.525"
www.sdparts.com
Great post and information, thank you!!
I use nothing but Brad Penn in my flat tappet cam vehicles. I wiped a lobe on my Pontiac bracket engine 3 years ago...never again!!
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Old 04-24-2010, 09:53 AM
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Quote:
Originally Posted by techinspector1
In this case, you're looking at 110 on the seat. The rate on those springs is 348 lbs per inch, so if you multiply your highest valve lift (0.465) times the rate, you will find out how much additional pressure will be exerted on the cam with the valve open. 348 times .465 = 162 lbs. Add 110 to 162 and you find an over the nose pressure of 272 lbs. This is well within my personal limit of 290 lbs. I don't use flat tappet cams any more, but when I did, I wouldn't recommend more than 290 lbs over the nose after the oil debacle. If the motor won't rev to where you want it to with 290 lbs, change to a roller cam.
I always love reading your info. I keep learning more and more...
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Old 04-24-2010, 10:14 AM
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You can just buy z28 springs at the local machine shop, pull the inner dampner and run them on the stock setup to 470" without changing anything else.

If you want more than 470 lift the issue is not really the guide as many have led everybody to believe, it's the valve seal itself occupying .100" .. so one can simply change to another type of valve seal (ie 2.2l chrysler) and run upwards of 550" with a set of circle track z28 +100" springs. have done it many times.
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