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| | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | 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 | | | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | 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 In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
| | | | | Joined: Feb 2000 Posts: 5,191 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,191 | Use this site, https://www.blocklayer.com/degree-wheeleng.aspx to build your custom degree wheel. Just add the data from the cam card, and you have a degree wheel just for that cam! | | | | | Joined: Feb 2004 Posts: 29,742 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,742 | 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
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | 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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