Labor Day Putting down your wrenches or time for
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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
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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: 5,190 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,190 | 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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