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Old 01-26-2004, 02:29 AM
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Vortec Heads / Max Lift?

I'm running a set of Vortec heads that have been the the machine shop. The machinist installed new springs, screw in studs, and guide plates.

I also drilled out the pushrod holes and gasket-matched the ports when I got them home.

I'm running a cam w/ a lift of .480
I've been told that the max lift out of a Vortec head is .420....

"The limitation is the clearance between the bottom of the retainer and the top of the valve-guide seal. total 0.450 retainer-to-seal clearance. Max. Valve Lift: 0.420 which allows 0.030 retainer-to-seal."

When I picked up the heads, I talked to the machinest and we sat down and looked through a book he had w/ cams in it. We chose a Comp Cams 280H, I reminded him about the heads, and he said everything was ok. He checked all the numbers a few times also.

But now that I am doing my own research, it doesn't seem to add up..... Heads say max .420, Cam says .480... can just replacing the springs make it safe for that much lift??

I don't know much about the Vortec head, or any head for that matter, so any help is greatly appreciated.

Thanks
Sean Stratton

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Old 01-26-2004, 02:32 AM
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Do a thread subject search on this. That cam is not going to work with those heads, you can get the heads machined to do it but right now you're in trouble. You're going to bend pushrods-

K
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Old 01-26-2004, 02:54 AM
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Well.... here's the situation.

I ran this motor for about a month w/ a Comp 274 flat-tappet cam.... then the cam went flat... the lift on the cam is .490.

Someone else built the motor and tuned it, the cam went flat, he moved, and i had to rebuild it and learn everything from scratch for the first time.

I ran that cam w/ the same heads... its a 383 stroker.... think that is why the cam went flat??

When I re-assembled the motor, I checked all the old pushrods, and none were bent. The old cam had about 200 miles on it before it went flat...

This new 280 cam is already in the car, the motor has been broken in, runs good, has about 100 miles on it....

What should I do??? I'm so new ive never had this problem.... And this is the first time i've realized what the whole scenario is... cause I never knew why the cam went flat.. but now i think i know....

Thanks again
Sean Stratton

Vortec Heads:
"if you plan to use a cam with more lift than .470 then you`ll need to have the guides clearenced so no interference occurs."


_____ Is that true?_____

- Sean

Last edited by onecoomofo; 01-26-2004 at 02:54 AM.
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Old 01-26-2004, 03:00 AM
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.480 is pushing the limits of luck with vortec heads! You say that it is broke in and seems fine, I say lucky you! You will very likely run into interference at extended r.p.m. it the lifters pump up or you get into a valve float r.p.m. level (like on a missed shift)! It's not that big of a process to get the guides machined down on these heads, or even buy the cutter and do it yourself! Sure you have to teardown the topend down and buy some new gaskets but that's a small price to pay to avoid engine damage and failure in the near future!
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Old 01-26-2004, 08:45 AM
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Anyone else? I need to get this worked out as this is my daily driver!

-Sean
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Old 01-26-2004, 09:38 AM
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there`s been several articles i`ve seen on the vortec heads, some say .480, I`ve seen .460, and one .470 before interference occured, but, the heads still must be clearenced to run these heads with bigger cams, no doubt about it. not sure if a interference problem would cause the cam to go flat, cams usually go flat from lack of lube or inproper break in procedure. was the engine ran from 1800 - 2200 RPM for 20 minutes during break in? are the oil drain back holes in the lifter valley plugged? where the oil gallery plugs removed and the gallery`s cleaned during the rebuild? if so were all the plugs reinstalled? what kind of oil pressure does the engine have?
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Old 01-26-2004, 11:34 AM
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Here's an update on my situtation:

I called up the machinest, and since he worked on the heads about 8 months ago, he couldn't quite remember what springs he used on them.

However, he told me to get a feeler gauge, remove the valve cover, and wait for one of the valves to open completely, and check the clearances. He said I should have ~.030" clearance and I would be OK.

Well I checked, and the springs never hit the gauge, so I guess i'm cool with the .480" lift.

Thanks for everyone's help.
Sean Stratton
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Old 01-26-2004, 12:25 PM
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The limiting factor here is not the spring, it is the height of the valve guide boss. Your machinist should have spot faced the guide down a little. If he left them as-is then you have a problem that only taking the heads back off will cure.
Normal machining on a Vortec head entails cutting down the guide boss height to allow for more lift and cutting down the lower portion of the guide boss diameter to allow a performance spring with a damper or a dual spring to be installed. I cut mine down .125" in height and that gives you plenty of clearance for .550" valve lift.
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Old 01-26-2004, 01:43 PM
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With proper spring clearance and guide to retainer clearance the head is not limited to any certain cam lift. I have several cam profiles in customer circle track engines running .650" lift on flat tappet stuff.

Chris
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Old 01-26-2004, 04:06 PM
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Do you guys think that I am OK since I checked the springs w/ the feeler gauge?

Sean Stratton
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Old 01-26-2004, 05:01 PM
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Don't take chances. You keep asking for everyone's advise but still you don't seem to listen. You must retain some acceptable clearance between the retainer and the guide boss to allow for valve bounce. Now if you don't machine down the guide bosses then you're gonna have to run with the standard vortec springs which are way too light - hence the need for the extra clearance. Do yourself a favor - get the guide bosses machined low and narrow and put a set of dual springs on that are matched to the cam grind. On the other hand why don't you step down a cam grind or 2? Check out this crate engine. It's running a cam with 0.460" exhaust lift whilst using the unmodified vortec heads! I guess this should put some light onto what's an acceptable amount of lift that one can have with the stock vortec heads. Some knuckle heads are saying 0.420" is the max!

http://www.sdpc2000.com/cart.asp?act...id=120&pid=115
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Old 01-26-2004, 06:32 PM
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Cool

Everything I have read on Vortecs says .480 is the max lift with stock heads. Why take a chance and run 'em on the edge when Comp Cams sells a cutter that allows you to do the work yourself? Saw it in Chevy High Performance. You should give Comp a call about some new "beehive" springs they have. I believe there is an article in a different Chevy High Performance that stated the beehive shape of the sprngs allowed them to handle more lift but they didn't have to have the spring pocket enlarged or the bosses cut down. It might be worth a call to Comp, it's a TOLL FREE NUMBER.
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Old 01-26-2004, 09:07 PM
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according to gm the max lift for those heads with the springs provided is 480
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Old 01-26-2004, 09:56 PM
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Quote:
Originally posted by club327
Don't take chances. You keep asking for everyone's advise but still you don't seem to listen. You must retain some acceptable clearance between the retainer and the guide boss to allow for valve bounce. Now if you don't machine down the guide bosses then you're gonna have to run with the standard vortec springs which are way too light - hence the need for the extra clearance. Do yourself a favor - get the guide bosses machined low and narrow and put a set of dual springs on that are matched to the cam grind. On the other hand why don't you step down a cam grind or 2? Check out this crate engine. It's running a cam with 0.460" exhaust lift whilst using the unmodified vortec heads! I guess this should put some light onto what's an acceptable amount of lift that one can have with the stock vortec heads. Some knuckle heads are saying 0.420" is the max!
Don't worry, I am taking the advice I ask for, and I thank everyone for it.

But before you shake your finger at me, remember I stated that i have DIFFERENT springs on these heads... That is why I am curious if my setup will work.

So, thanks for the help club327, or should I say knuckle head?

BTW I didn't machine down the 'guide bosses' and I'm _not_ running stock springs....

-Sean Stratton
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Old 01-27-2004, 12:13 AM
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Ok Sean. Sorry about not getting my facts straight lol. Sounds like you're well and truly in control with your project now. Rob
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