[mkpontiac]

From what I can find advertised hydraulic flat tappet cam durations are measured at:
Comp 0.006"
Crower 0.006" ?
Crane 0.004"
Pontiac .004" or .006"?
Summit ?
Lunati ?

Are these correct? Does anyone have a cam card that specifies? Please help me fill in the blanks?

Thanks,
Mark

[Tim Corcoran]

Now days it's difficult to know for sure. Some companies the marketing department will just make up the advertised duration number and it won't be based on duration at any lift. It would be nice if there was a standard but there isn't. At least there is a standard for the @.050 numbers.

[Old Man Taylor]

There is no standard for "advertised" duration. That's why 0.050" became a standard.

[Jack Gifford]

Those numbers- .004", 006", etc.- look like they are for a hydraulic cam. An unofficial "standard" for hydraulic cams is .006".

In earlier days, advertised duration for a solid-lifter cam was at the specified clearance values. But that was back when cam grinders were fussy about providing perfectly-sloped clearance ramps- with a distinct transition to the lobe's flank. Some companies still do the old-school ramps, but many don't bother- in which case, I don't know their definition of seat timing.

[mkpontiac]

Thank you for the replies. That explains why I am having trouble finding the information for most of them.

I wanted to calculate some dynamic compression ratios and compare pontiac cams to common aftermarket cams and also to "fast ramp" designs all with similiar at 0.050 duration numbers.

[mkpontiac]

From either contacting the company or finding the information on their website I was able to confirm the following lift points for advertised duration on hydraulic flat tappet cams:

Comp Cams 0.006"
Crane 0.004"
Crower 0.006"
Isky For the 256/262 cam 0.008". Some of their designs are at different lifts.
Lunati 0.006"

So if the actual numbers are consistent with what they indicate, direct comparisons can be made between at least the Comp, Crower and Lunati. You could also estimate the Isky by adding about 10° and the Crane by subtracting about 10°.

Mark

[Fishin2Deep4U]

The isky cam I have is .007" open, .010" closed.

This is 284/ 292 advertised. 236/ 244 @ .050"

Dave