What's the difference between duration , and advertised duration?
Here are the specs for a cam I'm thinking about buying for a 10.5 comp. 327 bored .60 over. What do you guys think? Will it sound good with a set of hooker sidepipes w/ JCL baffles?
Hydraulic Cam:
* Advertised duration: 290 degrees intake/297 degrees exhaust
* Duration @ .050 in.: 235 degrees intake/240 degrees exhaust
* Gross valve lift: .473 in. intake/.488 in. exhaust
* Lobe separation: 112 degrees



[Modified by corvettemaster, 2:47 PM 2/8/2003]

 

[QUOTE]What's the difference between duration , and advertised duration?
Here are the specs for a cam I'm thinking about buying for a 10.5 comp. 327 bored .60 over. What do you guys think? Will it sound good with a set of hooker sidepipes w/ JCL baffles?
Hydraulic Cam:
* Advertised duration: 290 degrees intake/297 degrees exhaust
* Duration @ .050 in.: 235 degrees intake/240 degrees exhaust
* Gross valve lift: .473 in. intake/.488 in. exhaust
* Lobe separation: 112 degrees


Advertised duration, or just plain ole duration is the amount expressed in degrees the valve is in motion. Duration at .050 is the amount in degrees the vavle is in motion after it has moved .050 of an inch. Due to different ramp angles on the cam advertised duration does not always tell the whole story, so most guys look at duration at .050 to get an idea what or how much duration a cam has.

When the valve first starts to move duration starts (advertised duration) the valve continues to open then reaches .050 of an inch opening (duration at .050 starts) the valve continues to open reaches max lift then comes down (closing) when the valve reaches .050 from the seat duration at .050 ends. The valve continues to close and when it does advertised duration ends.

As for the cam you are looking at for your 327 it should have a pretty good soundlig idle to it. The 112 lobe center with smooth it out a little, but it will still rumble pretty good. That is a fair amount of duration for a 327, especially with a hydraulic cam. They tend to sound bigger than a similar sized solid cam.

 

Advertised duration is from the time the lifter is moved about .004 - .006 until it is the same distance from closing. (varies from manufacturer) Duration at .050 is from the time the lifter moves .050 up until it is .050 away from closing.

Advertised duration can be very misleading because the lobe can have a very slow ramp (long duration) or a very fast ramp (short duration) and still act the same to the motor.

Comparing two cams is much easier if you look at .050 duration numbers.

 

I wouldn't think you need a split duration/lift cam with those headers.


[Modified by 63Banshee, 2:18 PM 2/8/2003]