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Jan 21st, 2020
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Joined: Dec 2008
Posts: 1,708
OP
'Bolter
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I've been asked "I have the valve opening & closing points of a cam, but how do I calculate the intake and exhaust centerlines, and the LSA or lobe center angle?"
Using the McGurk #18 data:
For the intake lobe: (intake closing - intake opening) / 2, then add 90 degrees
Example for 10-55 timing: 55 - 10 = 45, divide by 2 = 22.5, add 90 = 112.5 degrees ATDC
For the exhaust lobe: (exhaust opening - exhaust closing) / 2, then add 90 degrees
Example for 72-32 timing: 72 - 32 = 40, divide by 2 = 20, add 90 = 110 degrees BTDC
LSA: (intake CL + exhaust CL) / 2
112.5 + 110 = 222.5 / 2 = 111.25 degrees
I just wrote an Excel spreadsheet that calculates this automatically from your input, e-mail me for a free copy: jdiamond (at) optonline.net
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Joined: Jan 2013
Posts: 1,679
'Bolter
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Good school Panic, only thing missing is how to determine cam advance ground into the cam.
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h004101964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
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Joined: Feb 2004
Posts: 24,744
Kettle Custodian (pot stirrer)
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Thanks, Joe! Added to my "favorites" list!
BTW- - - -has anybody else thought about drilling and tapping the snout of a stovebolt cam and using a harmonic balancer installer to push the timing gear on?
Jerry
"Freedom's just another word for nothing left to lose"
Kris Kristofferson
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self.
Ernest Hemingway
WAG MORE- - - - - -BARK LESS!
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Joined: Dec 2008
Posts: 1,708
OP
'Bolter
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Typically the suggested (or already selected) intake lobe center is 4 degrees advanced from the CL.
More advance closes up the intake valve-to-piston clearance, more retard closes up the exhaust-valve-to-piston clearance.
Overlap and LSA are constants (at least, in single cam engines!).
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