extra info on cam duration...
C. What's with the different Duration Specs?:
1. "Advertised duration" is the duration @ 0.015 in., 0.020 in., or 0.030 in. valve lift (i.e. whatever the cam manufacturer wants to quote for duration at the lowest readable valve lift on the camshaft degree wheel when they degree the cams on install).
The Society of Automotive Engineers (SAE) chose this as their standard reference for when to measure duration . It is easier to read the dial indicator and cam degree wheel (when you degree your cams) at 0.015-0.030 in. than at the very start of when the valve starts to lift. So the engineers chose the lowest valve lift point to take a cam reading that was also the easiest to read.
Other Standardized Valve Lift Points to Read Duration Spec from:
2. Domestic V8 cam manufacturers reported their cam duration @ 0.050 in. valve lift. This has been their standard.
3. Japanese cam manufacturers report their cam duration @ 0.04 in. (or @1mm).
The lower the lift from which the duration is taken, the bigger the number for duration.
So there are 3 standards from which any person can list their duration specs. To compare between different cam manufacturers' profiles, howver, you must find the duration spec @ the same lift. Obviously, advertised duration sounds the best for marketing hype because it is the largest duration number of the 3 standards. Remember this fact and don't get fooled by a sales pitch quoting no reference lift. If there is no reference lift for the duration spec, you have to assume that it is "advertised duration" and not. When you shop between cams from different brands, make sure you use the or 0.04 in. or 0.05 in. lift quote for duration to compare apples to apples between them. A "300 degree duration" may not automatically it is bigger than a cam quoted as 270 duration @ 0.05 in. Compare using the same standard quoted lift.
Bottomline: Be careful when you read and compare duration specs between 2 different cam makers...make sure they are using the same lift reference point for the duration spec.
