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Cam DoctorCam Doctor - The Quickest Camshaft Education You'll Ever Get
by Don Terrill ©2004

The Cam Doctor is a computer camshaft checking machine that can spit out an unbelievable amount of data - more than the average human could ever understand. Quadrant Scientific, a company that is unfortunately no longer in business, developed this groundbreaking product.

What the Cam Doctor can do: Measure cam lobes
What the Cam Doctor can't do: Design cam lobes


The simplest data you'll get is the actual cam card data. This may come as a surprise to some, but the cam card you receive with your cam is not a measurement of your cam, it's what the cam is supposed to be. So, the Cam Doctor allows you to double-check the manufacturer. Rarely do they screw up, but it does happen.

Did someone grind the numbers off your camshaft? Not to fear, the Cam Doctor is better than any private investigator you could ever hire, well maybe. I actually had a customer take a cam I had sold him to a private investigator to see if the cam numbers could be recovered from where I had ground them off - I sold cams, not cam educations. To my disbelief it worked and the customer got the cam numbers - you'd have thought he decoded an ancient treasure map. So, if you ever run across an ass hole like me, you'll have two options for finding out what your cam is.

The Cam Doctor can do much more than just print out a cam card though. Print out the raw data and you'll see...

  • Crank location (Degrees)
  • Lifter location (inches)
  • Velocity (Inches of lift/Degrees of Crank rotation)
  • Acceleration (Rate of change of Velocity)
  • Jerk (Rate of change of Acceleration)
  • Quirk (Rate of change of Jerk) If you can understand this data you belong at NASA.

What can be learned from this data?

  • Where the lash should be set - You can only hit the lifter with so much initial velocity. I've tested enough cams that I can now look at the raw Cam Doctor data and find a great starting point for the lash. In fact, after dyno/track testing, I always seem to end up in the same velocity range.
  • Basecircle runout - Too much runout on a hydraulic cam could trick the lifter into thinking it should open the valve too soon, which would be a huge power killer. On solid lifter cams it's not as big a deal, but will effect your actual lash from cylinder to cylinder. Making some looser than you think and some tighter than you think.
  • Style of the ramps - For example: constant velocity open - this is where the lifter acceleration goes to zero for a while during the initial phase of valve opening.
  • Smallest flat tappet lifter diameter you can run - As the lifter gets bigger in diameter, the lifter velocity can go up. This is the reason for the constant velocity lobes - they go to the max velocity the lifter can take and just hang there.
  • Style of the nose - For example, some lift limited rule cams will have the lifter acceleration go to zero for a long period over the nose, in other words the nose is flat. It makes for a very distinct graph when printed out.
  • Are the opening and closing ramps the same? - Did the cam designer treat the open and close ramps differently? This is something you'd never know by the cam card and may play a huge role in its performance.
  • Why does one cam out perform another on the dyno or track? - Compare them on the cam doctor and you may know why. Focus on the opening and closing ramps.
  • Calculate piston to valve clearance between two cams, rocker ratios or intake centerline settings - This can be very handy. Once you baseline the piston to valve clearance by actual measurement, you can then calculate any change without ever measuring again. Want to change the rocker ratio? Look at the lobe lift at the tightest P to V point to calculate the change. Other changes can be done the same way.
  • Valve opening at max piston speed - Wouldn't it be interesting to know how far the intake valve is open when the piston is pulling its hardest? Damn right.
  • Area under the curve - This is the area of the lift vs. duration curve. Basically, the total amount air the engine could theoretically let in or out. I don't pay much attention to this number, probably because I haven't seen any direct correlation between it and performance.
  • Actual valve open and close - .020 lobe lift is the checking point most cam companies use for advertised duration and open/close events on solid lifter cams. Well, what if you're comparing a cam that was designed to run .016 lash with one that runs .028? You're not going to get an accurate enough picture to compare the two and may end up making a poor cam decision.

Cam Checking hardware and software:

www.audietech.com
www.andrews-products.com
www.performancetrends.com

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* Read Don Terrill's Technical Racing Column at http://raceology.com.


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