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Highest lift on stock spings and rocker arms??
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Rebel68343 View Drop Down
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    Posted: Oct/21/2008 at 11:44am
Hi guys I was just wondering and had this question in my head.
 
I have a 68 343 v8 motor with the 52 cc heads and was wondering what the highest lift the stock springs would take and also what about the rocker arm. The cam I have is the one for sale on the fourm but if I can't sell it I will use it.
 
-Specs 234-244 @50
-520-542 lift intake exhuast
 
Is this a bit too much for stock springs and rocker arm. I do already have hardending pushrods for the motor.
Your guys opinions and knowledge is appreciated. thanks!
 
 
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FuzzFace2 View Drop Down
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Points: 10356 		Post Options Post Options   Thanks (0) Thanks(0)   Quote FuzzFace2 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/21/2008 at 1:01pm

Well when I did my drag 360 junk yard rebuild (stock 360 lower end 291c heads) I had the same question when looking for a cam. Because I had 4.56 gears and a 4000 stall convert I needed some thing that could work in the upper range. The other thing I had no time or money for machine work to the heads.

A call to Summit came back with comp cams 280H with 490 lift as the biggest I could go with out work to heads so that is what I went with.

When I installed it I did all the normal checks like valve to piston, retainer to guide and coil bind and all where ok.

Some have said 520 is max with stock untouched heads. The other thing is how much lift can stock rockers take? I did not care as I was using a set of roller rockers from my blown up 304 and I don’t know if that 520 was for stock rockers or not also.

Dave ----
TSM = Technical Service Manual

75 Gremlin X v8 for sale
70 Javelin 360/auto drag car
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Scott H View Drop Down
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You can lengthen the slots in stock rockers. It is important to lengthen a bit more than needed for the lift of the cam. I like to see at least 0.05 clearance against the stud at full lift. It is also important to do this measurement with each rocker stud on the engine. How far you can safely elongate I don't know. FWIW, I have done this up to .585 lift.  Beyond that lift, you are are probably better off buying after market roller rockers and 7/16 studs because4 you will be needing heavyier springs too.
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poormansMACHINE View Drop Down
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Why would you want to use a new race cam with stock 40 year old parts?
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I agree. with poormansMACHINE.  Replacing the rocker studs with adjustable studs and a relatively inexpensive set of roller rockers is cheap insurance to ensure that you can optimize your nice new big lift cam.
Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
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Rebel68343 View Drop Down
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Thanks for those who chimed in, I understand what you guys are talking about.

But the question was also because if I sell the Crower camshaft, I wanted to see my limits as to what camshaft to get.
My plan was originally to buy crower cam kit- springs, retainers, lifters and some HS roller rockers.
Just wanted to know the limits of my stock parts is all.
thanks
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poormansMACHINE View Drop Down
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Originally posted by Rebel68343 Rebel68343 wrote:

Thanks for those who chimed in, I understand what you guys are talking about.

But the question was also because if I sell the Crower camshaft, I wanted to see my limits as to what camshaft to get.
My plan was originally to buy crower cam kit- springs, retainers, lifters and some HS roller rockers.
Just wanted to know the limits of my stock parts is all.
thanks

Well, NOT using stock springs and rockers, I'd say a .490" lift. Any more runs a risk of hitting the tops of the stock uncut valve guides.
As far as extending slots on old used rockers, personally I wouldn't do it.
After years and hours of operation, a wear pattern develops. extending the slot to go beyond that now has the rocker going over a step once it passes the max lift point from the old cam. Wear will be accelerated at the pivot and the tip.
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