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PostPosted: Sun Jan 13, 2019 10:51 am 
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Joined: Fri Jan 19, 2018 7:37 am
Posts: 30
I have a 72 351 CJ motor that I am assuming right now has stock pistons in it. Note that I am going to confirm the pistons when I pull the heads to have them machined for studs. I will also do the clay check method for checking. Right now I just want to see if the cam that I have will be ok from a clearance standpoint with stock pistons if that is truly what I have. The specs of the cam are Advertised Duration 299/319, Lift .579/.563.

https://www.summitracing.com/parts/cca-32-602-8/overview/make/ford

Thanks
Wade


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PostPosted: Mon Jan 14, 2019 5:35 am 
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Joined: Mon Oct 29, 2012 9:05 am
Posts: 2518
No way of knowing until you check.

The biggest enemy of PV clearance is overlap and that cam has a ton of it.

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Brent Lykins, Lykins Motorsports
www.lykinsmotorsports.com
brent@lykinsmotorsports.com


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PostPosted: Mon Jan 14, 2019 10:01 am 
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Joined: Mon Oct 29, 2012 1:52 pm
Posts: 532
Also where you place the cam in the engine can make a tremendous difference in the piston to valve clearance. I don't have those particular Comp lobes in my library but using my own DM242 hydraulic roller lobe as an example is quite interesting:

With the DM426 lobe and a 1.72 rocker on a 108 degree intake centerline valve lift at 10 degrees ATDC is .217, move that lobe ahead 4 degrees to 104 and now it has .246 lift at the same crank position. Move it forward one more time to a 102 intake centerline and it now has .260 valve lift at 10 degrees ATDC. That's quite a bit of change in only 6 degrees about .040.


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