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Old 04-30-2013, 03:41 PM
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How much can Pontiac pressed in studs take?

I want this Lunati Cam for my P350: Duration @ .050 (Int/Exh): 213/219
(Int/Exh): .455/.468 LSA/ICL: 112/108 RPM Range: 1000-5300. The whole Kit and Kaboodle has valve springs in it with seat pressure 120 and open pressure at 330. I read on Crane's website that open seat pressure over 280 was too much for press in Studs. Lunati guy said press in Studs in my 68 Le Mans 350 heads should be fine. Will 320 open pressure be too much? Or can I run the same cam with a weaker spring?

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Old 04-30-2013, 04:23 PM
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Quote:
Originally Posted by Nuck Chorris View Post
I want this Lunati Cam for my P350: Duration @ .050 (Int/Exh): 213/219
(Int/Exh): .455/.468 LSA/ICL: 112/108 RPM Range: 1000-5300. The whole Kit and Kaboodle has valve springs in it with seat pressure 120 and open pressure at 330. I read on Crane's website that open seat pressure over 280 was too much for press in Studs. Lunati guy said press in Studs in my 68 Le Mans 350 heads should be fine. Will 320 open pressure be too much? Or can I run the same cam with a weaker spring?
I've read different values from different sources, but would agree with the 280 lbs max.

I know this is old school stuff, but that doesn't mean it doesn't work.
http://www.summitracing.com/parts/mrg-806g
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Old 04-30-2013, 05:39 PM
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At 280 lbs over the nose , you better get screw ins put in.
320 over the nose is way too high for the cam suggested. 275-280 is fine.
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Old 04-30-2013, 06:54 PM
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I guess I didn't pay enough attention to the original post. Thanks Latech for your post. A fellow should be able to use stock springs with that cam.
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Old 04-30-2013, 07:08 PM
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Stock springs are real close to the specs for the crower springs most poncho guys run.
Used springs wont be though...LOL
I used crower 68404 springs on my build. I am running a crane 272-2 .
Those springs would be plenty for the cam OP suggested.
I am running them on a cam with .480 on the exhaust. Over the nose pressure was 278 lbs. on the exhaust.
Pressure at installed height was around 125 lbs IIRC
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Old 05-01-2013, 03:52 AM
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thanks for the replies, you helped me figure out that what I was told was false.
I was really confused, because what you guys said made sense and what the Lunati rep said did not. I did more research. On the Camshaft warehouse website I was able to find all the part numbers of the camshaft kit. LUNATI VALVE SPRINGS #73949 is the valve spring in the Voodoo kit. It does not have 330 open like the rep told me in an email. It has 120 seat at 1.65 and 265 open. Which will work with my pressed in Studs I believe.
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Old 05-01-2013, 08:33 AM
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Pulled Studs Not Fun

If your getting the heads done, get the studs pinned at a minimum. Its worth the extra few bucks. I built a mild 350 and did not have the studs pinned. Apparently, number 2 cylinder had an issue with the intake stud and it pulled. Made a hell of a racket and driving it home was miserable. Having to fix what should have been no issue made me a believer that pinned studs or screw in studs are worth it no matter what cam and spring combo you use.
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Old 05-01-2013, 09:53 AM
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why not just replace the heads? with a screw in type stud.
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Old 05-01-2013, 09:53 AM
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The problem with pressed in bottle-neck studs pulling out is just one of the problems. If it was, you could merely pin them.

If you increase the spring load more than 110 lb. on the seats and 280 lb. open, you risk snapping the studs at the bottle neck.

If you have an aftermarket camshaft with a cam lobe base circle diameter smaller than 1.330", you will not be able to set the lifter pre-load at 20 lb. torque.

You should therefore convert to fully adjustable valve train with 7/16"-20 or 3/8"-24 rocker studs. Cam grinders can get up to a maximum of .470" valve lift (.313" lobe lift) with a 1.330" cam lobe base circle and still use a non-adjustable valve train. It pays them to do so because they can sell more camshafts that way since their customers do not have to install screw in rocker studs and convert to a fully adjustable valve train. Cam grinders have discovered it is risky to have more than .450" valve lift (.300" lobe lift) with a 1.330" base circle or you risk breaking the stock bottle neck rocker studs. The cam grinders let you find that out the hard way after they have your money.

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Old 05-01-2013, 01:10 PM
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screw in stud heads expensive, too big of valves for the size of the bore, and if we go down that road why not just get some Ebrock heads for my Firebird? Or build another cookie cutter 383? The purpose of the build is to make 300-330 hp without major machining costs. The 69 Firebird is being built for as a spirited back roads cruiser. I've got Front discs on my mind, Koni shocks, sway bars, sub connectors, not to mention painting it.
Haven't found a machinist that is willing to pin the heads. I myself would not be that excited to drill 16 hardened studs either.
Thank you for telling me about the camshaft base circle. I had never heard of that before. Why does having a smaller base circle affect the non adjustable valve train? I am skeptical. Why would more than .45 lift with 1.3 base snap a stud? How do I find out what a cam's base circle is? Do I have to write Lunati to find out?
I find it hard to imagine that the stud will snap, because what I am building what I believe is not a radical combo. It's a 7/16 stud, and appears to be 3/8 at the threaded portion, and I assume these studs are stronger than grade 8 bolts.
thanks for your replies,
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Old 05-01-2013, 02:24 PM
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The base circle of the camshaft determines the distance from the rocker arm jamming shoulder so the pre load can be set and locked by the rocker arm nut tapered seat. If the distance is changed by using a camshaft with a smaller base circle, the 20 lb. of torque needed to lock the rocker nut to the bottleneck rocker stud cannot be met. You can still lock the pre load setting by using SB Chevrolet 3/8"-24 lock nuts a couple of times before the treads are worn out.

You can measure the cam lobe base circle with a pair of cheap vernier calipers ($10 at Harbor Freight) and it can be done with the camshaft in the engine on Pontiacs. If you call Lunati, they probably don't know what a cam lobe base circle is and if they did, you should not trust the informational they provide.

The 3/8"-24 bottleneck stud gives the stock screw-in or pressed in rocker studs a weak point and a place to break. They have a 7/16" shank but that is not where they break. The stock studs break at the tapered rocker nut seat between the 3/8"-24 threads and the 7/16" shank.

It is not the .450" valve lift that snaps a stud but the increased valve spring pressure caused by the extra lift can break a stock bottleneck rocker stud. Stock Pontiac valve springs coil bind at .526" valve lift which makes .470" the maximum valve lift with stock valve springs. An extra 125 lb. open pressure with stock valve springs is enough to break a bottleneck rocker arm stud. Some cam grinders prefer not to press the limit of .470" valve lift but use .450" valve lift as the limit with a 1.330" base circle for an added margin of safety. That was done in order to sell more camshafts to happy customers that are using stock bottleneck rocker studs. You can break stock bottleneck studs just by switching to 1.6:1 rocker arms.


The reason a 1.330" base circle and .313" lobe lift is the limit is because 1.643" is at the design limit for the camshaft to fit through 1.8687" diameter cam bearings. That leaves .113" clearance between the cam lobes and cam bearings. Lunati holds that limit to .0150" for their cams before they reduce the diameter of the cam lobe base circles.

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Old 05-02-2013, 03:59 PM
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Let me get a few something straight.
If the cam has a base circle of 1.330 then I can run it the stock set up.
The lift of the cam on the exhaust side is .468, which is a half a hair under .470.
Seat pressure is 120 which is just under 125.
It seems that so long as the base circle is good I might get away with running this cam.
Do I have this right?
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Old 05-02-2013, 04:44 PM
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Quote:
Originally Posted by Nuck Chorris View Post
It seems that so long as the base circle is good I might get away with running this cam.
Do I have this right?
The key word in your post is "might". Are you willing to take that chance?
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Old 05-02-2013, 05:05 PM
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As long as the base circle of the cam lobes are 1.330" in diameter and the push rods are from 9.130" to 9.150" long, the stock tapered seat bottleneck rocker studs used the stock tapered seat rocker nuts will lock the lifter pre load setting of .053" to .073" from zero pre load, depending on on the length of the push rods. .

I would be concerned about the stock bottleneck rocker studs breaking with more than 100 lb. seat pressure and more than 280 lb. open pressure. Pontiac never exceeded 118 lb. seat pressure and 280 lb. open pressure with 3/8" bottle neck rocker studs.

Before I discovered the problem with the stock bottle neck studs on a ten month old 1969 Firebird 400, I broke a bottle neck rocker stud using a Z300 Crane camshaft that had 125 lb. seat pressure and 300 lb. open pressure at .485" valve lift. I switched to BB Chevy rocker studs and the problem was solved. Fortunately I was in the waiting line at a drive-in movie when it happened. I learned that the hard way before Al Gore invented the internet.
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Old 05-02-2013, 08:12 PM
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so is getting 300-320hp from a pontiac 350 really this much of a PITA? at this point I would think the best bet would be to stick the numbers matching 350/350 in the corner of the garage and stick a chevy mill in it.
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