In looking at the Competition Cams selections I see a cam with "Advertised Duration" of 260/260 with lift of .440/.440. This is a mild High Energy cam.

In looking at the specs of the factory camshaft for my 327/210 in "Chevy by the numbers" it says the stock cam had .390 intake, .410 exhaust, 310 intake duration, 320 exhaust duration, and 1.5 rockers. All the other hotter small blocks for '67 show even more duration. This seems like a LOT of duration compared to the specs on cams I see for sale.

Did they change the way this is measured? If so, how do the modern cams numbers relate to the old ones?

Thanks for any info,

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Damon Linkous
'67 Camaro Z21
http://www.linkpro.net/camaro

Question too boring?

G.M. measured a cam's TOTAL duration, including deflection. Comp. and most others measure a cam at .050" valve lift which is the effective area of the cam. This is called checking clearances when degreeing a cam.

companies are getting more aggressive with quick valve opening lobes. The time the valve is open is equal to the area of the lobe apart from the cam's base circle. If the old cam has a long duration and low lift, it gets whatever area. Nowadays, cam technology does the reverse... go shorter duration and more lift to get the same amount of valve open time. This design allows for similar power, but with a better idle, and driveability. Also by opening and closing the valves faster you get less bleeding off of cylinder pressure.

Thanks for the info.