Please explain what cam specs. mean !!!
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Please explain what cam specs. mean !!! (Arisa)
A cam starts as a round bar of steel, which is ground down to a smaller circle with "lobes" protruding from that "base circle". As the cam rotates, at 1/2 the crankshaft speed, the valve lifters ride up and down, following these lobes.
When you see cam lift (or lobe height off the base circle) plot vs crankshaft angle it looks like two bells. These represent the lift due to the actual cam lobes.
The distance, in degrees, between the point where the curve just starts to show lift and the point where it goes back to zero lift is the dwell for that lobe, i.e. intake or exhaust lobe.
Since this "zero lift" point was hard to define and standardize on, the distance between the two points of 0.050" of lift was chosen as a standard rating.
The number of degrees between the center of the intake lobe and the exhaust lobe, the LSA, is a measure of overlap or time when both valves are partly open.
That's the basic idea; for a thorough explanation of cams and valve trains, selection and installation along with pics go to the Comp Cams web site and get their catalogue. It's not only a great primmer but is quite useful when selecting/installing camshaft and valve train components.
When you see cam lift (or lobe height off the base circle) plot vs crankshaft angle it looks like two bells. These represent the lift due to the actual cam lobes.
The distance, in degrees, between the point where the curve just starts to show lift and the point where it goes back to zero lift is the dwell for that lobe, i.e. intake or exhaust lobe.
Since this "zero lift" point was hard to define and standardize on, the distance between the two points of 0.050" of lift was chosen as a standard rating.
The number of degrees between the center of the intake lobe and the exhaust lobe, the LSA, is a measure of overlap or time when both valves are partly open.
That's the basic idea; for a thorough explanation of cams and valve trains, selection and installation along with pics go to the Comp Cams web site and get their catalogue. It's not only a great primmer but is quite useful when selecting/installing camshaft and valve train components.
Pro
Joined: Jun 2001
Posts: 697
Likes: 0
From: College Station Tx
Re: Please explain what cam specs. mean !!! (Arisa)
Safety Car
Joined: Nov 1999
Posts: 3,891
Likes: 2
From: Houston, TX
Re: Please explain what cam specs. mean !!! (ChrisB)
Looks like ChrisB beat me to it!!! 
This is a perfect time to announce the population of the tech section of our site though. Look for updates on a weekly or more basis! I hope that you guys find them helpful and informative.
Thanks,
This is a perfect time to announce the population of the tech section of our site though. Look for updates on a weekly or more basis! I hope that you guys find them helpful and informative.
Thanks,
Melting Slicks
Joined: Apr 2000
Posts: 3,198
Likes: 2
From: Northern CA
Re: Please explain what cam specs. mean !!! (Arisa)
See if you can get hold of a Comp Cams catalog. It has a very good, detailed description of how the whole valvetrain works. There's also an excellent graph of a cam profile with labels of the various specs (LSA, duration, etc)
