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Old 08-27-2003, 01:35 PM   #14
techworkseng
Scooby Newbie
 
Member#: 21604
Join Date: Jul 2002
Location: Calgary, Alberta, Canada
Default advertised cam spefications

Here is the facts on what apears to many as misrepresentation of cam specification differences between manufacturers.
Cam specs are only comparable if the cam lobe profiles compared are absolutely identical. Not a likely situation. Also, you may have noticed that some manufacturers use different lift points to indicate duration. Some use .050" lift as the measurement point, I tend to use .040" because it is equal to 1mm and is the number we most often used during our superbike development phase. This is done to eliminate introducing long acceleration ramps into the duration measurement. It also provides a more consistent point to determine lobe center angles and lobe seperation angles.
Now, you may ask, why don't manufacturers just specify lift at several angles of measurement. Well, a savvy engineer, given enough of these data points, could perform a spline curve extrapolation, and quickly come up with a fairly representative cam lobe profile on his/her own. The simple way to steal a manufacturers design is to buy one set of cams and have them profiled by another cam grinder. TWE has been a victim of this of this in the past (There are more "TWE profile" cams in cars out there than we have sold).

At TWE we employ the following method of developing cam profiles.
-Flow bench (preferrably pulsing, so duration based flow numbers can be gathered, and mass flow aproximations can be perfomed) data must be gathered.
- Velocity gradients are determined with flow bench pitot tube measurements.
- All above data is integrated over the valve actuation/lift domain using numerical iteration methods (Software) until the maximum total mass flow per cycle is achieved.
- Empirical testing (dyno, road testing, acceleration) is used to fine tune lobe centers and lobe seperation.

The preceding is a very generalised overview of our cam development technique at TWE.

Tom Penner
Research and Development
Tech Works Engineering Inc.
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