Author Topic: Factory Camshaft spec's for 1967 L48  (Read 1448 times)

maroman

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Re: Factory Camshaft spec's for 1967 L48
« Reply #15 on: August 08, 2022, 05:04:36 PM »
Excellent explanation. Thank you both for the follow up. I knew there had to be good reasoning to the process.
Doug  '67 RS/SS 396 auto I know the car since new

crossboss

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Re: Factory Camshaft spec's for 1967 L48
« Reply #16 on: August 10, 2022, 10:41:59 PM »
Couldn't they just pull the lifter and place the dial indicator direct to the lobe?

The protocol for an NHRA "teardown" was specified by the organization.  Obviously, there is more than one way to accomplish the same end but NHRA used the solid lifter method during the inspection ritual therefore, that was the most reliable way to avoid unpleasant outcomes.  For example, measuring lift directly off the lobe would have left plenty of room for a knowledgeable builder to capitalize on rocker arm ratios, pushrod length, etc. to beat the specified lift measurement by a few thousandths and thereby gain an edge.  If that seems to be an anachronism, it was really nothing compared to some of the other procedures that were routinely followed.  A casual observer would have been mesmerized by the process for checking camshaft duration and overlap using a dial caliper, a dial indicator, a Sharpie or lead pencil, and a strip of masking tape.  Of course, the problems of attaining an acceptable degree of accuracy using that procedure eventually led to the abandonment of the duration spec for stock camshafts in NHRA competition.  Meantime, in order to compete in their game, we measured the lift/duration and overlap on every cylinder, the open/closed valve spring pressures on every cylinder, sorted through buckets of stock rocker arms to find the 16 that would produce favorable lift numbers, poured every combustion chamber and head runner to determine legal volumes, and a bunch of other factors every time an engine was built or freshened.  In retrospect, it probably wasn't worth the effort but, in order to appreciate it, you really needed to be there.  During the early years, a Stocker "teardown" session at the U.S. Nationals or the Winternationals could have included as many as fifty or sixty cars and the "barn" would have been in operation for at least 10 or 12 hours.


Slightly off topic, but relative...
I have a friend who runs in C/Stock automatic class. 'Back in the day', tear downs were common to check if anyone was cheating. Of course most were. (Smokey Unick said "IF you ain't cheatn', you ain't winning!") Remember, a 'Stock camshaft' in NHRA is not your typical street cam grind. Many factors are 'allowable' such as ramp angles, etc. This is why they sound quite radical. Essentially, they are 'cheater cams' to us. Back to my friend, who was a record holder at many events, was running some 'cheater' heads...aka acid flowed. He sold them to me during the late 1980s. They 'looked' stock to the casual observer...
Just another T/A fanatic. A new project in the works.