Friday

Picking the Right Camshaft



Picking the Right Camshaft

By Don Terrill (c)2006

What needs to be decided and in what order:
  1. Lobe Family - This is a group of lobes that have similar open/close ramps, but different durations. I truly believe the smartest thing Comp Cams every did was publish lobe specs in the back of their catalog - it instantly made me a fan.
  2. Intake Duration - If I had never run a Spin-Tron this would be my number one. Get intake duration and lobe family correct and you're 90% there.
  3. Exhaust Duration - This maybe number three on the list, but is actually a long way from the importance of the first two.
  4. Lobe Separation - Take every lobe separation you've ever seen run with your application, place them on a dart board, close your eyes and throw. That's how relatively important this spec is.
Before I continue I want to talk about something I've noticed on most message boards - whenever someone mentions that something is not important, they are immediately hammered with "Yes it is!!!" Don't let these people stop you from practicing the 80/20 principle.

Questions that need to be answered:
  • Engine Size - Use to pick durations.
  • RPM Range - Use to pick durations.
  • Rocker Ratio - Use to pick lobe family and durations.
  • Valvetrain Weight - Use to pick lobe family.
  • Valve Springs - Use to pick lobe family.
  • Exhaust Flow - Use to finalize exhaust duration
Questions that only need to be answered when you're trying to look smart:
  • Cylinder Heads
  • Runner CCs
  • Intake Manifold
  • Compression
  • Valve Size
  • Header Size
  • And on and on and on...
That fact is, even if you're trying to set a nation record, those questions don't need to be answered. Dyno and track testing will be the only way to get the perfect cam. The goal is to get in the ballpark and adjust from there.

And finally, the following question only needs to be answered when you're trying to look stupid:
  • Tire Size - If you don't find this funny, you haven't called many cam companies.
Want to send off a nasty email about how wrong I am? Well, first read this and then write your own article.